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HEATER CORE RADIATOR UPPER HOSE TO WATER PUMP RADIATOR WATER PUMP TO COOLANT PULLEY RECOVERY BOTTLE RADIATOR LOWER HOSE7-2 COOLING SYSTEM XJGENERAL INFORMATION (Continued) An optional factory installed heavy duty cooling WATER PUMPSpackage is available on most models. The package A quick test to determine if the pump is working isconsists of a radiator that has an increased number to check if the heater warms properly. A defectiveof cooling fins. Vehicles equipped with a 4.0L 6- cyl- water pump will not be able to circulate heated cool-inder engine and heavy duty cooling and/or air con- ant through the long heater hose to the heater core.ditioning also have an auxiliary electric cooling fan. COOLANTCOOLING SYSTEM COMPONENTS The cooling system is designed around the coolant. The cooling system consists of: Coolant flows through the engine water jackets • A radiator absorbing heat produced during engine operation. • Cooling fan (mechanical and/or electrical) The coolant carries heat to the radiator and heater • Thermal viscous fan drive core. Here it is transferred to the ambient air pass- • Fan shroud ing through the radiator and heater core fins. The • Radiator pressure cap coolant also removes heat from the automatic trans- • Thermostat mission fluid in vehicles equipped with an automatic • Coolant reserve/overflow system transmission. • Transmission oil cooler (if equipped with anautomatic transmission) RADIATORS • Coolant 2.5L 4–cylinder engine radiators are the down flow • Water pump type, 4.0L 6-cylinder engine radiators are the cross • Hoses and hose clamps flow type. Plastic tanks are used on all radiators.SYSTEM COOLANT ROUTING CAUTION: Plastic tanks, while stronger than brass, For cooling system flow routings, refer to (Fig. 1) are subject to damage by impact, such as(Fig. 2). wrenches. Fig. 1 Coolant Flow—2.5L 4-Cylinder Engine—Typical
TO COOLANT RADIATORWATER PUMP HEATER CORE TANK HOUSING OVERFLOW THERMOSTAT RESERVE/XJ COOLING SYSTEM 7-3GENERAL INFORMATION (Continued) ENGINE BLOCK HEATER An optional engine block heater is available for all models. The heater is equipped with a power cord. The cord is attached to an engine compartment com- ponent with tie-straps. The heater warms the engine providing easier engine starting and faster warm-up in low temperatures. The heater is mounted in a core hole of the engine cylinder block (in place of a freeze plug) with the heating element immersed in engine coolant. Connect the power cord to a grounded 110- 120 volt AC electrical outlet with a grounded, three- wire extension cord. DESCRIPTION AND OPERATION AUTOMATIC TRANSMISSION OIL COOLER WATER-TO-OIL COOLER All models equipped with an automatic transmis- sion are equipped with a transmission oil cooler mounted internally within the radiator tank. This internal cooler is supplied as standard equipment on all models equipped with an automatic transmission. Transmission oil is cooled when it passes through this separate cooler. In case of a leak in the internal radiator mounted transmission oil cooler, engine cool- ant may become mixed with transmission fluid or transmission fluid may enter engine cooling system. Fig. 2 Coolant Flow—4.0L 6-Cylinder Engine— Both cooling system and transmission should be Typical drained and inspected if the internal radiator If the plastic tank has been damaged, the plastic mounted transmission cooler is leaking.tank and/or o-rings are available for service repair.Tank replacement should be done by a qualified per- AIR-TO-OIL COOLERson with proper equipment. An auxiliary air-to-oil transmission oil cooler is available with most engine packages.ACCESSORY DRIVE BELT TENSION The auxiliary air-to-oil transmission oil cooler is Correct accessory drive belt tension is required to located in front of the radiator or A/C condenser (ifensure optimum performance of belt driven engine equipped) and behind the grill. It is mounted to theaccessories. If specified tension is not maintained, front frame crossmember.belt slippage may cause: engine overheating, lack of The auxiliary oil coolers on all models operate inpower steering assist, loss of air conditioning capac- conjunction with the internal radiator mounted mainity, reduced generator output rate, greatly reduced oil cooler. The transmission oil is routed through thebelt life and objectionable under hood noise. main cooler first, then the auxiliary cooler, before returning to the transmission.DOMESTIC LEFT HAND DRIVE VEHICLES Belt tension is adjusted at the power steering COOLANT RESERVE/OVERFLOW SYSTEMpump bracket and idler pulley assembly. The system works along with the radiator pressure cap. This is done by using thermal expansion andDOMESTIC RIGHT HAND DRIVE VEHICLES contraction of the coolant to keep the coolant free of If equipped with a 4.0L 6-cylinder engine; the ser- trapped air. It provides:pentine belt is adjusted at the generator mounting • A volume for coolant expansion and contraction.bracket. When equipped with a 2.5L 4-cylinder • A convenient and safe method for checking/ad-engine, the serpentine belt is adjusted at the power justing coolant level at atmospheric pressure. This issteering pump bracket and idler pulley assembly. done without removing the radiator pressure cap. • Some reserve coolant to the radiator to cover minor leaks and evaporation or boiling losses.
MOUNTING CLAMP BOLTS TUBE TO RADIATOR COOLANT TANK OVERFLOW RESERVE/ LOWER BRACKET7-4 COOLING SYSTEM XJDESCRIPTION AND OPERATION (Continued) As the engine cools, a vacuum is formed in thecooling system of both the radiator and engine. Cool-ant will then be drawn from the coolant tank andreturned to a proper level in the radiator. The coolant reserve/overflow system consists of aradiator mounted pressurized cap, a plastic reserve/overflow tank (Fig. 3) (Fig. 4), a tube (hose) connect-ing the radiator and tank, and an overflow tube onthe side of the tank. Fig. 4 Reserve/Overflow Tank—With Right Hand Drive tested (between two pulleys) to check tension. Do not allow the gauge (or gauge adapter) to contact any- thing but the belt. ENGINE BLOCK HEATER An optional engine block heater is available for all models. The heater is equipped with a power cord. The cord is attached to an engine compartment com- Fig. 3 Reserve/Overflow Tank—Except Right Hand ponent with tie-straps. The heater warms the engine Drive providing easier engine starting and faster warm-up in low temperatures. The heater is mounted in a coreCOOLING SYSTEM FANS hole of the engine cylinder block (in place of a freeze Also refer to either the Viscous Fan Drive and/or plug) with the heating element immersed in enginethe Auxiliary Electric Cooling Fan. coolant. Connect the power cord to a grounded 110- All models are equipped with a mechanical temper- 120 volt AC electrical outlet with a grounded, three-ature controlled fan. This thermal viscous fan drive wire extension cord.is a torque-and-temperature-sensitive clutch unit. Itautomatically increases or decreases fan speed to WARNING: DO NOT OPERATE ENGINE UNLESSprovide proper engine cooling. Vehicles with a 4.0L BLOCK HEATER CORD HAS BEEN DISCONNECTED6-cylinder engine may also have an auxiliary electri- FROM POWER SOURCE AND SECURED IN PLACE.cal cooling fan; when equipped air conditioningand/or heavy duty cooling. BLOCK HEATER SPECIFICATIONS • 2.5L 4-Cylinder Engine: 115 Volts 400 WattsACCESSORY DRIVE BELT TENSION • 4.0L 6-Cylinder Engine: 120 Volts 600 Watts Both the 2.5l and 4.0l engines use one accessorydrive belt. Correct drive belt tension is required to THERMOSTATensure optimum performance of the belt driven A pellet-type thermostat controls the operatingengine accessories. There are different types of temperature of the engine by controlling the amountadjustment gauges for checking either a serpentine of coolant flow to the radiator. On all engines theor a conventional “V-type” belt. Refer to the instruc- thermostat is closed below 195°F (90°C). Above thistions supplied with the gauge. Make sure to use a temperature, coolant is allowed to flow to the radia-gauge designed specifically for serpentine style belts. tor. This provides quick engine warm-up and overallPlace gauge in the middle of the section of belt being temperature control.
XJ COOLING SYSTEM 7-5DESCRIPTION AND OPERATION (Continued) An arrow plus the word UP is stamped on the and water is -32 deg. C (-26 deg. F). 5 deg. C higherfront flange next to the air bleed. The words TO than ethylene-glycol’s freeze point. The boiling pointRAD are stamped on one arm of the thermostat. (protection against summer boil-over) of propylene-They indicate the proper installed position. glycol is 125 deg. C (257 deg. F ) at 96.5 kPa (14 psi), The same thermostat is used for winter and sum- compared to 128 deg. C (263 deg. F) for ethylene-gly-mer seasons. An engine should not be operated with- col. Use of propylene-glycol can result in boil-over orout a thermostat, except for servicing or testing. freeze-up in Chrysler vehicles, which are designed forOperating without a thermostat causes other prob- ethylene-glycol. Propylene glycol also has poorer heatlems. These are: longer engine warm-up time, unre- transfer characteristics than ethylene glycol. Thisliable warm-up performance, increased exhaust can increase cylinder head temperatures under cer-emissions and crankcase condensation. This conden- tain conditions.sation can result in sludge formation. Propylene-glycol/Ethylene-glycol Mixtures—Should Not BeCAUTION: Do not operate an engine without a Used in Chrysler Vehiclesthermostat, except for servicing or testing. Propylene-glycol/ethylene-glycol Mixtures can cause the destabilization of various corrosion inhibi- tors, causing damage to the various cooling systemCOOLANT PERFORMANCE components. Also, once ethylene-glycol and propy- lene-glycol based coolants are mixed in the vehicle,ETHYLENE-GLYCOL MIXTURES conventional methods of determining freeze point will The required ethylene-glycol (antifreeze) and water not be accurate. Both the refractive index and spe-mixture depends upon the climate and vehicle oper- cific gravity differ between ethylene glycol and propy-ating conditions. The recommended mixture of 50/50 lene glycol.ethylene-glycol and water will provide protectionagainst freezing to -37 deg. C (-35 deg. F). The anti- CAUTION: Richer antifreeze mixtures cannot befreeze concentration must always be a minimum of measured with normal field equipment and can44 percent, year-round in all climates. If percentage cause problems associated with 100 percent ethyl-is lower than 44 percent, engine parts may be ene-glycol.eroded by cavitation, and cooling system com-ponents may be severely damaged by corrosion.Maximum protection against freezing is provided COOLANT SELECTION-ADDITIVESwith a 68 percent antifreeze concentration, which Coolant should be maintained at the specified levelprevents freezing down to -67.7 deg. C (-90 deg. F). A with a mixture of ethylene glycol-based antifreezehigher percentage will freeze at a warmer tempera- and low mineral content water. Only use an anti-ture. Also, a higher percentage of antifreeze can freeze containing ALUGARD 340-2 .cause the engine to overheat because the specificheat of antifreeze is lower than that of water. CAUTION: Do not use coolant additives that are claimed to improve engine cooling.100 Percent Ethylene-Glycol—Should Not Be Used inChrysler Vehicles Use of 100 percent ethylene-glycol will cause for- RADIATOR PRESSURE CAPmation of additive deposits in the system, as the cor- All radiators are equipped with a pressure cap.rosion inhibitive additives in ethylene-glycol require This cap releases pressure at some point within athe presence of water to dissolve. The deposits act as range of 83-110 kPa (12-16 psi). The pressure reliefinsulation, causing temperatures to rise to as high as point (in pounds) is engraved on top of the cap (Fig.149 deg. C (300) deg. F). This temperature is hot 5).enough to melt plastic and soften solder. The The cooling system will operate at pressuresincreased temperature can result in engine detona- slightly above atmospheric pressure. This results in ation. In addition, 100 percent ethylene-glycol freezes higher coolant boiling point allowing increased radi-at 22 deg. C (-8 deg. F ). ator cooling capacity. The cap contains a spring- loaded pressure relief valve that opens when systemPropylene-glycol Formulations—Should Not Be Used in pressure reaches release range of 83-110 kPa (12-16Chrysler Vehicles psi). Propylene-glycol formulations do not meet A vent valve in the center of cap allows a smallChrysler coolant specifications. It’s overall effec- coolant flow through cap when coolant is below boil-tive temperature range is smaller than that of ethyl- ing temperature. The valve is completely closed whenene-glycol. The freeze point of 50/50 propylene-glycol boiling point is reached. As the coolant cools, it con-
VACUUM VENT VALVE (SHOWN IN SEAL- CROSS-SECTIONAL VIEW ING POSITION) TOP VIEWPRESSURE RATING SEAL PRESSURE VALVE FILLER NECK ROTATION DIRECTIONVIEW R STAMPED INTO IMPELLER FRONT VIEWED AS ROTATION DIRECTIONVIEW BACK VIEWED AS7-6 COOLING SYSTEM XJDESCRIPTION AND OPERATION (Continued) cous fan drive assembly. REVERSE is stamped or imprinted on the cover of the viscous fan drive and inner side of the fan. The letter R is stamped into the back of the water pump impeller (Fig. 6). Fig. 6 Reverse Rotating Water Pump—Typical Engines from previous model years, depending Fig. 5 Radiator Pressure Cap and Filler Neck— upon application, may have been equipped with a for- Typical ward (clockwise) rotating water pump. Installation oftracts and creates a vacuum in the cooling system. the wrong water pump will cause engine overheating.This causes the vacuum valve to open and coolant in A quick test to determine if the pump is working isthe reserve/overflow tank to be drawn through its to check if the heater warms properly. A defectiveconnecting hose into radiator. If the vacuum valve is water pump will not be able to circulate heated cool-stuck shut, the radiator hoses will collapse on cool- ant through the long heater hose to the heater core.down. A rubber gasket seals radiator filler neck. This is COOLING SYSTEM HOSESdone to maintain vacuum during coolant cool-down Rubber hoses route coolant to and from the radia-and to prevent leakage when system is under pres- tor, intake manifold and heater core. Radiator lowersure. hoses are spring-reinforced to prevent collapse from water pump suction at moderate and high engineWATER PUMPS speeds. A centrifugal water pump circulates coolant WARNING: CONSTANT TENSION HOSE CLAMPSthrough the water jackets, passages, intake manifold, ARE USED ON MOST COOLING SYSTEM HOSES.radiator core, cooling system hoses and heater core. WHEN REMOVING OR INSTALLING, USE ONLYThe pump is driven from the engine crankshaft by a TOOLS DESIGNED FOR SERVICING THIS TYPE OFdrive belt on all engines. CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER The water pump impeller is pressed onto the rear 6094) (Fig. 7). SNAP-ON CLAMP TOOL (NUMBERof a shaft that rotates in bearings pressed into the HPC-20) MAY BE USED FOR LARGER CLAMPS.housing. The housing has a small hole to allow seep- ALWAYS WEAR SAFETY GLASSES WHEN SERVIC-age to escape. The water pump seals are lubricated ING CONSTANT TENSION CLAMPS.by the antifreeze in the coolant mixture. No addi-tional lubrication is necessary.CAUTION: All engines are equipped with a reverse(counter-clockwise) rotating water pump and vis-
LETTER HOSE CLAMP NUMBER/ CLAMPCONSTANT TYPICAL HOSE 6094 LOCA- TENSION TION TOOL CLAMP TYPICAL HOSE HOSECLAMP THERMOSTATIC FAN DRIVE VISCOUS SPRING MOUNTING HUBXJ COOLING SYSTEM 7-7DESCRIPTION AND OPERATION (Continued)CAUTION: A number or letter is stamped into the Ordinary worm gear type hose clamps (whentongue of constant tension clamps (Fig. 8). If equipped) can be removed with a straight screw-replacement is necessary, use only an original driver or a hex socket. To prevent damage toequipment clamp with matching number or letter. hoses or clamps, the hose clamps should be tightened to 4 N·m (34 in. lbs.) torque. Do not over tighten hose clamps. VISCOUS FAN DRIVE NOTE: Also refer to Cooling System Fans. The thermal viscous fan drive is a silicone-fluid- filled coupling used to connect the fan blades to either the engine or the water pump shaft. The cou- pling allows the fan to be driven in a normal manner. This is done at low engine speeds while limiting the top speed of the fan to a predetermined maximum level at higher engine speeds. A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit. A typical viscous unit is shown in (Fig. 9). This spring coil Fig. 7 Hose Clamp Tool—Typical reacts to the temperature of the radiator discharge air. It engages the viscous fan drive for higher fan speed if the air temperature from the radiator rises above a certain point. Until additional engine cooling is necessary, the fan will remain at a reduced rpm regardless of engine speed. Fig. 9 Typical Viscous Fan Drive Fig. 8 Clamp Number/Letter Location Only when sufficient heat is present, will the vis- Inspect the hoses at regular intervals. Replace cous fan drive engage. This is when the air flowinghoses that are cracked, feel brittle when squeezed, or through the radiator core causes a reaction to theswell excessively when the system is pressurized. bimetallic coil. It then increases fan speed to provide For all vehicles: In areas where specific routing the necessary additional engine cooling.clamps are not provided, be sure that hoses are posi- Once the engine has cooled, the radiator dischargetioned with sufficient clearance. Check clearance temperature will drop. The bimetallic coil againfrom exhaust manifolds and pipe, fan blades, drive reacts and the fan speed is reduced to the previousbelts and sway bars. Improperly positioned hoses can disengaged speed.be damaged, resulting in coolant loss and engineoverheating.
POWER RIGHT FENDER DISTRIBUTION CENTER BATTERY7-8 COOLING SYSTEM XJDESCRIPTION AND OPERATION (Continued)CAUTION: Engines equipped with serpentine drivebelts have reverse rotating fans and viscous fandrives. They are marked with the word REVERSE todesignate their usage. Installation of the wrong fanor viscous fan drive can result in engine overheat-ing.CAUTION: If the viscous fan drive is replacedbecause of mechanical damage, the cooling fanblades should also be inspected. Inspect for fatiguecracks, loose blades, or loose rivets that couldhave resulted from excessive vibration. Replace fanblade assembly if any of these conditions arefound. Also inspect water pump bearing and shaftassembly for any related damage due to a viscousfan drive malfunction.NOISE It is normal for fan noise to be louder (roar-ing) when: • The underhood temperature is above the engage-ment point for the viscous drive coupling. This may Fig. 10 Power Distribution Center (PDC)occur when ambient (outside air temperature) is very DIAGNOSIS AND TESTINGhigh. • Engine loads and temperatures are high such as ON-BOARD DIAGNOSTICS (OBD)when towing a trailer. • Cool silicone fluid within the fan drive unit is COOLING SYSTEM RELATED DIAGNOSTICSbeing redistributed back to its normal disengaged The Powertrain Control Module (PCM) has been(warm) position. This can occur during the first 15 programmed to monitor the certain following coolingseconds to one minute after engine start-up on a cold system components:engine. • If the engine has remained cool for too long a period, such as with a stuck open thermostat, a Diag-AUXILIARY ELECTRIC COOLING FAN nostic Trouble Code (DTC) can be set. Models equipped with a 4.0L 6-cylinder engine may • If an open or shorted condition has developed inalso have an auxiliary electrical cooling fan. This is the relay circuit controlling the electric radiator fan,with models that have air conditioning and/or heavy a Diagnostic Trouble Code (DTC) can be set.duty cooling. The fan is controlled by the cooling fan If the problem is sensed in a monitored circuitrelay, which is located in the power distribution cen- often enough to indicate an actual problem, a DTC ister (PDC) (Fig. 10). For the location of relay within stored. The DTC will be stored in the PCM memorythe PDC, refer to the label on PDC cover. for eventual display to the service technician. (Refer When coolant temperature reaches approximately to Group 25, Emission Control Systems for proper103°C (218°F), or when air conditioning is requested, procedures)the powertrain control module (PCM) provides aground path for the fan relay. This ground is pro- ACCESSING DIAGNOSTIC TROUBLE CODESvided to the cooling fan relay through pin C2 of PCM To read DTC’s and to obtain cooling system data,connector C3. Battery voltage is then applied to the refer to Group 25, Emission Control Systems forfan through the relay. When coolant temperature proper procedures.drops below approximately 98°C (209°F), the PCMopens the ground path to the relay. This will prevent DRB SCAN TOOLthe cooling fan from being energized. For operation of the DRB scan tool, refer to the appropriate Powertrain Diagnostic Procedures ser- vice manual.
XJ COOLING SYSTEM 7-9DIAGNOSIS AND TESTING (Continued)ENGINE ACCESSORY DRIVE BELTSBELT DIAGNOSIS When diagnosing serpentine accessory drive belts,small cracks that run across the ribbed surface of thebelt from rib to rib (Fig. 11), are considered normal.These are not a reason to replace the belt. However,cracks running along a rib (not across) are not nor-mal. Any belt with cracks running along a rib mustbe replaced (Fig. 11). Also replace the belt if it hasexcessive wear, frayed cords or severe glazing. Refer to the Serpentine Drive Belt Diagnosischarts for further belt diagnosis. Fig. 11 Serpentine Belt Wear Patterns SERPENTINE BELT DIAGNOSIS CHART CONDITION POSSIBLE CAUSES CORRECTIONRIB CHUNKING (One or more ribs has 1. Foreign objects imbedded in pulley 1. Remove foreign objects from pulleyseparated from belt body) grooves. grooves. Replace belt. 2. Installation damage 2. Replace beltRIB OR BELT WEAR 1. Pulley misaligned 1. Align pulley(s) 2. Abrasive environment 2. Clean pulley(s). Replace belt if necessary 3. Rusted pulley(s) 3. Clean rust from pulley(s) 4. Sharp or jagged pulley groove tips 4. Replace pulley. Inspect belt. 5. Belt rubber deteriorated 5. Replace beltBELT SLIPS 1. Belt slipping because of insufficient 1. Adjust tension tension 2. Belt or pulley exposed to substance 2. Replace belt and clean pulleys that has reduced friction (belt dressing, oil, ethylene glycol) 3. Driven component bearing failure 3. Replace faulty component or bearing (seizure) 4. Belt glazed or hardened from heat 4. Replace belt. and excessive slippageLONGITUDAL BELT CRACKING 1. Belt has mistracked from pulley 1. Replace belt groove 2. Pulley groove tip has worn away 2. Replace belt rubber to tensile member
7 - 10 COOLING SYSTEM XJDIAGNOSIS AND TESTING (Continued) CONDITION POSSIBLE CAUSES CORRECTIONЉGROOVE JUMPING” 1. Belt tension either too low or too 1. Adjust belt tension(Belt does not maintain correct highposition on pulley) 2. Pulley(s) not within design 2. Replace pulley(s) tolerance 3. Foreign object(s) in grooves 3. Remove foreign objects from grooves 4. Pulley misalignment 4. Align component 5. Belt cordline is broken 5. Replace beltBELT BROKEN 1. Excessive tension 1. Replace belt and adjust tension to(Note: Identify and correct problem specificationbefore new belt is installed) 2. Tensile member damaged during 2. Replace belt belt installation 3. Severe misalignment 3. Align pulley(s) 4. Bracket, pulley, or bearing failure 4. Replace defective component and beltNOISE 1. Belt slippage 1. Adjust belt(Objectional squeal, squeak, or 2. Bearing noise 2. Locate and repairrumble is heard or felt while drive belt 3. Belt misalignment 3. Align belt/pulley(s)is in operation) 4. Belt to pulley mismatch 4. Install correct belt 5. Driven component induced 5. Locate defective driven component vibration and repair 6. System resonant frequency 6. Vary belt tension within induced vibration specifications.TENSION SHEETING FABRIC 1. Tension sheeting contacting 1. Correct rubbing conditionFAILURE stationary object(Woven fabric on outside, 2. Excessive heat causing woven 2. Replace beltcircumference of belt has cracked or fabric to ageseparated from body of belt) 3. Tension sheeting splice has 3. Replace belt fracturedCORD EDGE FAILURE 1. Excessive tension 1. Adjust belt tension(Tensile member exposed at edges of 2. Belt contacting stationary object 2. Replace beltbelt or separated from belt body) 3. Pulley(s) out of tolerance 3. Replace pulley 4. Insufficient adhesion between 4. Replace belt and adjust tension to tensile member and rubber matrix specificationsPRELIMINARY CHECKS TRAILER TOWING: Consult Trailer Towing section of owners manual.ENGINE COOLING SYSTEM OVERHEATING Do not exceed limits. Establish what driving conditions caused the com-plaint. Abnormal loads on the cooling system such as AIR CONDITIONING; ADD-ON OR AFTER MARKET:the following may be the cause: A maximum cooling package should have been ordered with vehicle if add-on or after market A/C isPROLONGED IDLE, VERY HIGH AMBIENT TEMPERATURE, installed. If not, maximum cooling system compo-SLIGHT TAIL WIND AT IDLE, SLOW TRAFFIC, TRAFFIC nents should be installed for model involved perJAMS, HIGH SPEED OR STEEP GRADES. manufacturer’s specifications. Driving techniques that avoid overheating are: • Idle with A/C off when temperature gauge is at RECENT SERVICE OR ACCIDENT REPAIR:end of normal range. Determine if any recent service has been per- • Increasing engine speed for more air flow is rec- formed on vehicle that may effect cooling system.ommended. This may be:
XJ COOLING SYSTEM 7 - 11DIAGNOSIS AND TESTING (Continued) • Engine adjustments (incorrect timing) NOTE: If investigation reveals none of the previous • Slipping engine accessory drive belt(s) items as a cause for an engine overheating com- • Brakes (possibly dragging) plaint, refer to following Cooling System Diagnosis • Changed parts. Incorrect water pump or pump charts.rotating in wrong direction due to belt not correctlyrouted These charts are to be used as a quick-reference • Reconditioned radiator or cooling system refill- only. Refer to the group text for information.ing (possibly under filled or air trapped in system).
7 - 12 COOLING SYSTEM XJDIAGNOSIS AND TESTING (Continued)COOLING SYSTEM DIAGNOSIS CONDITION POSSIBLE CAUSES CORRECTIONTEMPERATURE GAUGE READS 1. Has a Diagnostic Trouble Code 1. Refer to On-Board Diagnostics inLOW (DTC) number 17 been set indicating the service manual text. Replace a stuck open engine thermostat? thermostat if necessary. If a Diagnostic Trouble Code (DTC) number 17 has not been set, the problem may be with the temperature gauge. 2. Is the temperature gauge (if 2. Check the engine temperature equipped) connected to the sensor connector in the engine temperature gauge coolant sensor on compartment. Refer to Group 8E. the engine? Repair as necessary. 3. Is the temperature gauge (if 3. Check gauge operation. Refer to equipped) operating OK? Group 8E. Repair as necessary. 4. Coolant level low in cold ambient 4. Check coolant level in the coolant temperatures accompanied with poor reserve/overflow tank and the heater performance. radiator. Inspect system for leaks. Repair leaks as necessary. Refer to the Coolant section of the manual text for WARNINGS and precautions before removing the radiator cap. 5. Improper operation of internal 5. Inspect heater and repair as heater doors or heater controls. necessary. Refer to Group 24, Heating and Air Conditioning for procedures.TEMPERATURE GAUGE READS 1. Trailer is being towed, a steep hill is1. This may be a temporary conditionHIGH OR ENGINE COOLANT being climbed, vehicle is operated in and repair is not necessary. Turn offWARNING LAMP ILLUMINATES. slow moving traffic, or engine is being the air conditioning and attempt toCOOLANT MAY OR MAY NOT BE idled with very high ambient (outside) drive the vehicle without any of theLOST OR LEAKING FROM temperatures and the air conditioning previous conditions. Observe theCOOLING SYSTEM is on. Higher altitudes could aggravate temperature gauge. The gauge these conditions. should return to the normal range. If the gauge does not return to normal range, determine the cause for overheating and repair. Refer to POSSIBLE CAUSES (numbers 2 through 20). 2. Is temperature gauge (if equipped) 2. Check gauge. Refer to Group 8E. reading correctly? Repair as necessary. 3. Is temperature warning lamp (if 3. Check warning lamp operation. equipped) illuminating unnecessarily? Refer to Group 8E. Repair as necessary. 4. Coolant low in coolant reserve/ 4. Check for coolant leaks and repair overflow tank and radiator. as necessary. Refer to Testing Cooling System For Leaks in this group. 5. Pressure cap not installed tightly. If 5. Tighten cap. cap is loose, boiling point of coolant will be lowered. Also refer to the following step 6. 6. Poor seals at radiator cap. 6. (a) Check condition of cap and cap seals. Refer to Radiator Cap. Replace cap if necessary. (b) Check condition of radiator filler neck. If neck is bent or damaged, replace radiator. COOLING SYSTEM DIAGNOSIS
XJ COOLING SYSTEM 7 - 13DIAGNOSIS AND TESTING (Continued) CONDITION POSSIBLE CAUSES CORRECTIONTEMPERATURE GAUGE READS 7. Coolant level low in radiator but not 7. (a) Check condition of radiator capHIGH OR ENGINE COOLANT in coolant reserve/overflow tank. This and cap seals. Refer to Radiator CapWARNING LAMP ILLUMINATES. means the radiator is not drawing in this group. Replace cap if necessary.COOLANT MAY OR MAY NOT BE coolant from the coolant reserve/ (b) Check condition of radiator fillerLOST OR LEAKING FROM COOLING overflow tank as the engine cools. neck. If neck is bent or damaged,SYTEM (Continued) As the engine cools, a vacuum is replace radiator. formed in the cooling system of the (c) Check the condition of the hose engine and radiator. If radiator cap from the radiator to the coolant tank. It seals are defective, or cooling system should fit tight at both ends without any has leaks, a vacuum can not be kinks or tears. Replace hose if formed. necessary. (d) Check coolant reserve/overflow tank and tank hose for blockage. Repair as necessary. 8. Freeze point of antifreeze not 8. Check antifreeze. Refer to Coolant correct. Mixture may be too rich. section of this group. Adjust antifreeze- to-water ratio as required. 9. Coolant not flowing through system. 9. Check for coolant flow at radiator filler neck with some coolant removed, engine warm and thermostat open. Coolant should be observed flowing through radiator. If flow is not observed, determine reason for lack of flow and repair as necessary. 10. Radiator or A/C condenser fins are 10. Clean insects or debris. Refer to dirty or clogged. Radiator Cleaning in this group. 11. Radiator core is corroded or 11. Have radiator re-cored or replaced. plugged. 12. Aftermarket A/C installed without 12. Install proper radiator. proper radiator. 13. Fuel or ignition system problems. 13. Refer to Fuel and Ignition System groups for diagnosis. Also refer to the appropriate Powertrain Diagnostic Procedures service manual for operation of the DRB scan tool. 14. Dragging brakes. 14. Check and correct as necessary. Refer to Group 5, Brakes in this manual text. 15. Bug screen is being used reducing 15. Remove bug screen. airflow. 16. Thermostat partially or completely 16. Check thermostat operation and shut. This is more prevalent on high replace as necessary. Refer to mileage vehicles. Thermostats in this group. 17. Thermal viscous fan drive not 17. Check fan drive operation and operating properly. replace if necessary. Refer to Viscous Fan Drive in this group. 18. Electric cooling fan not operating 18. Check electric fan operation and properly (XJ models with 4.0L engine repair as necessary. Refer to Auxiliary equipped with heavy duty cooling Electric Cooling Fan-XJ Models with and/or air conditioning). 4.0L 6-cylinder engine in the manual text. COOLING SYSTEM DIAGNOSIS (CONT.)
7 - 14 COOLING SYSTEM XJDIAGNOSIS AND TESTING (Continued) CONDITION POSSIBLE CAUSES CORRECTIONTEMPERATURE GAUGE READS 19. Cylinder head gasket leaking 19. Check for cylinder head gasketHIGH OR ENGINE COOLANT leaks. Refer to Testing Cooling SystemWARNING LAMP ILLUMINATES. for Leaks in this group. For repair referCOOLANT MAY OR MAY NOT BE to Group 9, Engines.LOST OR LEAKING FROM COOLINGSYSTEM (Continued) 20. Heater core leaking. 20. Check heater core for leaks. Refer to Group 24, Heating and Air Conditioning. Repair as necessary.TEMPERATURE GUAGE READING IS 1. On XJ models equipped with a 4.0L 1. A normal condition. No correction isINCONSISTENT (FLUCTUATES, 6-cylinder engine, heavy duty cooling necessary. If gauge cycling is goingCCLES OR IS ERRACTIC) and/or air conditioning, the gauge may into the hot zone, check electric fan cycle up and down. This is due to the operation and repair as necessary. cycling of the electric radiator fan. Refer to Auxiliary Electric Cooling Fan-XJ Models with 4.0L 6-cylinder engine in the manual text. 2. During cold weather operation, with 2. A normal condition. No correction is the heater blower in the high position, necessary. the gauge reading may drop slightly. 3. Temperature gauge or engine 3. Check operation of gauge and repair mounted gauge sensor defective or if necessary. Refer to Group 8E, shorted. Also, corroded or loose wiring Instrument Panel and Gauges. in this circuit. 4. Gauge reading rises when vehicle is 4. A normal condition. No correction is brought to a stop after heavy use necessary. Gauge reading should (engine still running). return to normal range after vehicle is driven. 5. Gauge reading high after restarting a 5. A normal condition. No correction is warmed-up (hot) engine. necessary. The gauge should return to normal range after a few minutes of engine operation. 6. Coolant level low in radiator (air will 6. Check and correct coolant leaks. build up in the cooling system causing Refer to Testing Cooling Sytem for the thermostat to open late). Leaks in this group. 7. Cylinder head gasket leaking 7. (a) Check for cylinder head gasket allowing exhaust gas to enter cooling leaks with a commercially available system causing thermostat to open late. Block Leak Tester. Repair as necessary. (b) Check for coolant in the engine oil. Inspect for white steam emitting from exhaust system. Repair as necessary. 8. Water pump impeller loose on shaft. 8. Check water pump and replace as necessary. Refer to Water Pumps in this group. 9. Loose accessory drive belt (water 9. Refer to Engine Accessory Drive pump slipping). Belts in this group. Check and correct as necessary. 10. Air leak on the suction side of water 10. Locate leak and repair as pump allows air to build up in cooling necessary. system causing thermostat to open late. COOLING SYSTEM DIAGNOSIS (CONT.)
XJ COOLING SYSTEM 7 - 15DIAGNOSIS AND TESTING (Continued) CONDITION POSSIBLE CAUSES CORRECTIONPRESSURE CAP IS BLOWING OFF 1. Pressure relief valve in radiator cap 1. Check condition of radiator cap andSTEAM AND/OR COOLANT TO is defective. cap seals. Refer to Radiator Caps inCOOLANT TANK. TEMPERATURE this group. Replace cap as necessary.GAUGE READING MAY BE ABOVENORMAL BUT NOT HIGH. COOLANTLEVEL MAY BE HIGH IN COOLANTRESERVE/OVERFLOW TANKCOOLANT LOSS TO THE GROUND 1. Coolant leaks in radiator, cooling 1. Pressure test and repair asWITHOUT PRESSURE CAP system hoses, water pump or engine. necessary. Refer to Testing CoolingBLOWOFF. GAUGE IS READING System for Leaks in this group.HIGH OR HOTDETONATION OR PREIGNITION 1. Engine overheating. 1. Check reason for overheating and(NOT CAUSED BY IGNITION repair as necessary.SYSTEM). GAUGE MAY OR MAYNOT BE READING HIGH 2. Freeze point of antifreeze not 2. Check antifreeze. Refer to the correct. Mixture is too rich or too lean. Coolant section in this group. Adjust antifreeze-to-water ratio as required.HOSE OR HOSES COLLAPSE WHEN 1. Vacuum created in cooling system on 1. (a) Radiator cap relief valve stuck.ENGINE IS COOLING engine cool-down is not being relieved Refer to Radiator Cap in this group. through coolant reserve/overflow Replace if necessary. system. (b) Hose between coolant reserve/ overflow tank and radiator is kinked. Repair as necessary. (c) Vent at coolant reserve/overflow tank is plugged. Clean vent and repair as necessary. (d) Reserve/overflow tank is internally blocked or plugged. Check for blockage and repair as necessary.ELECTRIC RADIATOR FAN RUNS 1. Fan relay, powertrain control module 1. Refer to Auxiliary Electric CoolingALL THE TIME (XJ MODELS WITH (PCM) or engine coolant temperature Fan-XJ Models with 4.0L 6-Cylinder4.0L ENGINE EQUIPPED WITH sensor defective. engine in the manual text. Repair asHEAVY DUTY COOLING AND/OR AIR necessary. Also refer to appropriateCONDITIONING ONLY) Powertrain Diagnostic Procedures service manual for operation of the DRB scan tool.ELECTRIC RADIATOR FAN WILL NOT 1. Fan motor defective. 1. Refer to Auxiliary Electric CoolingRUN (XJ MODELS WITH 4.0L Fan-XJ Models with 4.0L 6-CylinderENGINE EQUIPPED WITH HEAVY engine in the manual text. Repair asDUTY COOLING AND/OR AIR necessary.CONDITIONING ONLY) GAUGE 2. Fan relay, powertrain control module 2. Refer to Auxiliary Electric CoolingREADING HIGH OR HOT (PCM) or engine coolant temperature Fan-XJ Models with 4.0L 6-Cylinder sensor defective. engine in the manual text. Repair as necessary. Also refer to the appropriate Powertrain Diagnostic Procedures service manual for operation of the DRB scan tool 3. Blown fuse in power distribution 3. Determine reason for blown fuse center (PDC). and repair as necessary. COOLING SYSTEM DIAGNOSIS (CONT.)
7 - 16 COOLING SYSTEM XJDIAGNOSIS AND TESTING (Continued) CONDITION POSSIBLE CAUSES CORRECTIONNOISY FAN 1. Fan blades loose. Replace fan blade assembly. Refer to Cooling System Fans in this group. 2. Fan blades striking a surrounding 2. Locate point of fan blade contact object. and repair as necessary. 3. Air obstructions at radiator or air 3. Remove obstructions and/or clean conditioning condenser. debris or insects from radiator or A/C condenser. 4. Electric fan motor defective (if 4. Replace electric fan motor. Refer to equipped). Auxiliary Electric Cooling Fan-XJ Models with 4.0L 6-Cylinder engine in the manual text. 5. Thermal viscous fan drive has 5. Replace fan drive. Bearing is not defective bearing. serviceable. Refer to Viscous Fan Drive in this group. 6. A certain amount of fan noise 6. Refer to Viscous Fan Drive in this (roaring) may be evident on models group for an explanation of normal fan equipped with a thermal viscous fan noise. drive. Some of this noise is normal.INADEQUATE AIR CONDITIONER 1. Radiator and/or A/C condenser is 1. Remove restriction and/or clean asPERFORMANCE (COOLING SYSTEM restricted, obstructed or dirty (insects, necessary. Refer to Radiator CleaningSUSPECTED) leaves etc.). in this group. 2. Electric radiator fan not operating 2. Refer to Auxiliary Electric Cooling when A/C is operated (if equipped with Fan-XJ Models with 4.0L 6-Cylinder electric fan). engine in the manual text. Repair as necessary. 3. Thermal viscous fan drive is 3. Refer to Viscous Fan Drive for freewheeling. diagnosis. Repair as necessary. 4. Engine is overheating (heat may be 4. Correct overheating condition. Refer transferred from radiator to A/C to text in Group 7, Cooling. condenser. High underhood temperatures due to engine overheating may also transfer heat to A/C components). 5. Some models with certain engines 5. Check for missing or damaged air are equipped with air seals at the seals and repair as necessary. radiator and/or A/C condenser. If these seals are missing or damaged, not enough air flow will be pulled through the radiator and A/C condenser.INADEQUATE HEATER 1. Has a diagnostic trouble code (DTC) 1. Refer to On-Board Diagnostics inPERFORMANCE. THERMOSTAT number 17 been set? the manual text and replace thermostatFAILED IN OPEN POSITION if necessary. 2. Coolant level low. 2. Refer to Testing Cooling System for Leaks in the manual text. Repair as necessary. 3. Obstructions in heater hose fittings at 3. Remove heater hoses at both ends engine. and check for obstructions. Repair as necessary. 4. Heater hose kinked. 4. Locate kinked area and repair as necessary. COOLING SYSTEM DIAGNOSIS (CONT.)
XJ COOLING SYSTEM 7 - 17DIAGNOSIS AND TESTING (Continued) CONDITION POSSIBLE CAUSES CORRECTIONINADEQUATE HEATER 5. Some models with certain engines 5. Refer to Group 24, Heating andPERFORMANCE. THERMOSTAT are equipped with a water control Air Conditioning for diagnosis. RepairFAILED IN OPEN POSITION valve located on one of the heater as necessary.(Continued) hoses. This valve may be defective. 6. Water pump is not pumping water 6. Refer to Water Pumps in this to heater core. When the engine is group. Repair as necessary. If a fully warmed up, both heater hoses slipping belt is detected, refer to should be hot to the touch. If only Engine Accessory Drive Belts in this one of the hoses is hot, the water group. Repair as necessary. pump may not be operating correctly. The accessory drive belt may also be slipping causing poor water pump operation.HEAT ODOR 1. Various heat shields are used at 1. Locate missing shields and certain drive line components. One or replace or repair as necessary. more of these shields may be missing. 2. Is temperature gauge reading 2. Refer to the previous Temperature above the normal range? Gauge Reads High in these Diagnosis Charts. Repair as necessary. 3. Is cooling fan operating correctly? 3. Refer to Cooling System Fan in this group for diagnosis. Repair as necessary. 4. Has undercoating been applied to 4. Clean undercoating as necessary. any unnecessary component? 5. Engine may be running rich 5. Refer to the DRB scan tool and causing the catalytic convertor to the appropriate Powertrain overheat. Diagnostic Procedures service manual. Repair as necessary.POOR DRIVEABILITY 1. For proper driveability, good 1. Refer to On-Board Diagnostics in(THERMOSTAT POSSIBLY STUCK vehicle emissions and for preventing this group. DTC’s may also beOPEN) GAUGE READING MAY BE build-up of engine oil sludge, the checked using the DRB scan tool.LOW thermostat must be operating Refer to the proper Powertrain properly. Has a diagnostic trouble Diagnostics Procedures service code (DTC) number 17 been set? manual for checking the thermostat using the DRB scan tool. Replace thermostat if necessary.STEAM IS COMING FROM FRONT 1. During wet weather, moisture 1. Occasional steam emitting fromOF VEHICLE NEAR GRILL AREA (snow, ice or rain condensation) on this area is normal. No repair isWHEN WEATHER IS WET, ENGINE the radiator will evaporate when the necessary.IS WARMED UP AND RUNNING, thermostat opens. This openingAND VEHICLE IS STATIONARY. allows heated water into the radiator.TEMPERATURE GAUGE IS IN When the moisture contacts the hotNORMAL RANGE radiator, steam may be emitted. This usually occurs in cold weather with no fan or airflow to blow it away. COOLING SYSTEM DIAGNOSIS (CONT.)
7 - 18 COOLING SYSTEM XJDIAGNOSIS AND TESTING (Continued) CONDITION POSSIBLE CAUSES CORRECTIONCOOLANT COLOR 1. Coolant color is not necessarily an 1. Refer to Coolant in this group for indication of adequate corrosion or antifreeze tests. Adjust antifreeze-to- temperature protection. Do not rely water ratio as necessary. on coolant color for determining condition of coolant.COOLANT LEVEL CHANGES IN 1. Level changes are to be expected 1. A normal condition. No repair isCOOLANT RESERVE/OVERFLOW as coolant volume fluctuates with necessary.TANK. TEMPERATURE GAUGE IS engine temperature. If the level in theIN NORMAL RANGE tank was between the FULL and ADD marks at normal engine operating temperature, the level should return to within that range after operation at elevated temperatures. COOLING SYSTEM DIAGNOSIS (CONT.)
TYPICAL COOLINGTESTER PRESSURE SYTEM TYPICAL BLACK LIGHT TOOLXJ COOLING SYSTEM 7 - 19DIAGNOSIS AND TESTING (Continued)RADIATOR COOLANT FLOW CHECK WARNING: HOT, PRESSURIZED COOLANT CAN The following procedure will determine if coolant is CAUSE INJURY BY SCALDING.flowing through the cooling system. If engine is cold, idle engine until normal operating Carefully remove the radiator pressure cap fromtemperature is reached. Then feel the upper radiator the filler neck and check the coolant level. Pushhose. If hose is hot, the thermostat is open and water down on the cap to disengage it from the stop tabs.is circulating through cooling system. Wipe the inner part of the filler neck and examine the lower inside sealing seat for nicks, cracks, paint,TESTING COOLING SYSTEM FOR LEAKS dirt and solder residue. Inspect the reserve/overflow tank tube for internal obstructions. Insert a wireULTRAVIOLET LIGHT METHOD through the tube to be sure it is not obstructed. All Jeep models have a leak detection additive Inspect the cams on the outside part of the filleradded to the cooling system before they leave the fac- neck. If the cams are bent, seating of pressure captory. The additive is highly visible under ultraviolet valve and tester seal will be affected. Replace cap iflight (black light). If the factory original coolant has cams are bent.been drained, pour one ounce of additive into the Attach pressure tester 7700 (or an equivalent) tocooling system. The additive is available through the the radiator filler neck (Fig. 13).part’s department. Place the heater control unit inHEAT position. Start and operate the engine untilthe radiator upper hose is warm to the touch. Aimthe commercially available black light tool at thecomponents to be checked. If leaks are present, theblack light will cause the additive to glow a brightgreen color. The black light can be used along with a pressuretester to determine if any external leaks exist (Fig.12). Fig. 13 Pressurizing System—Typical Operate the tester pump to apply 124 kPa (18 psi) pressure to the system. If the hoses enlarge exces- sively or bulge while testing, replace as necessary. Observe the gauge pointer and determine the condi- tion of the cooling system according to the following criteria: • Holds Steady: If the pointer remains steady for two minutes, there are no serious coolant leaks in the system. However, there could be an internal leak that does not appear with normal system test pres- sure. Inspect for interior leakage or do the Internal Leakage Test. Do this if it is certain that coolant is being lost and no leaks can be detected. • Drops Slowly: Shows a small leak or seepage is occurring. Examine all connections for seepage or Fig. 12 Leak Detection Using Black Light—Typical slight leakage with a flashlight. Inspect the radiator,PRESSURE TESTER METHOD hoses, gasket edges and heater. Seal any small leak The engine should be at the normal operating tem- holes with a Sealer Lubricant or equivalent. Repairperature. Recheck the system cold if the cause of leak holes and reinspect the system with pressurecoolant loss is not located during warm engine exam- applied.ination. • Drops Quickly: Shows that a serious leakage is occurring. Examine the system for serious external
7 - 20 COOLING SYSTEM XJDIAGNOSIS AND TESTING (Continued)leakage. If no leaks are visible, inspect for internal Drain sufficient coolant to allow for thermostatleakage. Large radiator leak holes should be repaired removal. Refer to Thermostat Replacement. Discon-by a reputable radiator repair shop. nect the water pump drive belt. Disconnect the upper radiator hose from the ther-INTERNAL LEAKAGE INSPECTION mostat housing. Remove the housing and thermostat. Remove the engine oil pan drain plug and drain a Install the thermostat housing.small amount of engine oil. Coolant, being heavier Add coolant to the radiator to bring the level tothan engine oil, will drain first. Another way of test- within 6.3 mm (1/4 in) of the top of the thermostating is to operate the engine and check for water glob- housing.ules on the engine oil dipstick. Also inspect theautomatic transmission oil dipstick for water glob- CAUTION: Avoid overheating. Do not operate theules. Inspect the automatic transmission fluid cooler engine for an excessive period of time. Open thefor leakage. Operate the engine without the pressure draincock immediately after the test to eliminatecap on the radiator until thermostat opens. boil over of coolant. Attach a pressure tester to the filler neck. If pres-sure builds up quickly, a leak exists as a result of a Start the engine and accelerate rapidly three timesfaulty cylinder head gasket or crack in the engine. (to approximately 3000 rpm) while observing theRepair as necessary. coolant. If internal engine combustion gases are leak- ing into the cooling system, bubbles will appear inWARNING: DO NOT ALLOW PRESSURE TO the coolant. If bubbles do not appear, there is noEXCEED 124 KPA (18 PSI). TURN THE ENGINE OFF. internal combustion gas leakage.TO RELEASE THE PRESSURE, ROCK THE TESTERFROM SIDE TO SIDE. WHEN REMOVING THE VISCOUS FAN DRIVETESTER, DO NOT TURN THE TESTER MORE THAN1/2 TURN IF THE SYSTEM IS UNDER PRESSURE. LEAKS Viscous fan drive operation is not affected by small If there is no immediate pressure increase, pump oil stains near the drive bearing. If leakage appearsthe pressure tester until the indicated pressure is excessive, replace the fan drive unit.within the system range. Vibration of the gaugepointer indicates compression or combustion leakage TESTINGinto the cooling system. If the fan assembly free-wheels without drag (the fan blades will revolve more than five turns whenWARNING: DO NOT DISCONNECT THE SPARK spun by hand), replace the fan drive. This spin testPLUG WIRES WHILE THE ENGINE IS OPERATING. must be performed when the engine is cool. For the following test, the cooling system must be in good condition. It also will ensure against exces-CAUTION: Do not operate the engine with a spark sively high coolant temperature.plug shorted for more than a minute. The catalyticconverter may be damaged. WARNING: BE SURE THAT THERE IS ADEQUATE FAN BLADE CLEARANCE BEFORE DRILLING. Isolate the compression leak by shorting eachspark plug to the cylinder block. The gauge pointer (1) Drill a 3.18-mm (1/8-in) diameter hole in theshould stop or decrease vibration when spark plug top center of the fan shroud.for leaking cylinder is shorted. This happens because (2) Obtain a dial thermometer with an 8 inch stemof the absence of combustion pressure. (or equivalent). It should have a range of -18°-to- 105°C (0°-to-220° F). Insert thermometer through theCOMBUSTION LEAKAGE TEST (WITHOUT hole in the shroud. Be sure that there is adequatePRESSURE TESTER) clearance from the fan blades. DO NOT WASTE reusable coolant. If the solution (3) Connect a tachometer and an engine ignitionis clean, drain the coolant into a clean container for timing light (timing light is to be used as a strobereuse. light). (4) Block the air flow through the radiator. SecureWARNING: DO NOT REMOVE THE CYLINDER a sheet of plastic in front of the radiator (or air con-BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR ditioner condenser). Use tape at the top to secure theDRAINCOCK WITH THE SYSTEM HOT AND UNDER plastic and be sure that the air flow is blocked.PRESSURE. SERIOUS BURNS FROM COOLANT (5) Be sure that the air conditioner (if equipped) isCAN OCCUR. turned off.
VACUUM VENT VALVE (SHOWN IN SEAL- ING POSITION) PRESSURE RATING SEAL PRESSURE VALVE FILLER NECKXJ COOLING SYSTEM 7 - 21DIAGNOSIS AND TESTING (Continued)WARNING: USE EXTREME CAUTION WHEN THE SHOULD NOT BE REMOVED WHILE THE SYSTEMENGINE IS OPERATING. DO NOT STAND IN A IS HOT AND/OR UNDER PRESSURE.DIRECT LINE WITH THE FAN. DO NOT PUT YOURHANDS NEAR THE PULLEYS, BELTS OR FAN. DONOT WEAR LOOSE CLOTHING. (6) Start the engine and operate at 2400 rpm.Within ten minutes the air temperature (indicated onthe dial thermometer) should be up to 88° C (190° F).Fan drive engagement should have started to occurat between 74° to 82° C (165° to 180° F). Engage-ment is distinguishable by a definite increase in fanflow noise (roaring). The timing light also will indi-cate an increase in the speed of the fan. (7) When the air temperature reaches 88° C (190°F), remove the plastic sheet. Fan drive disengage-ment should have started to occur at between 57° to79° C (135° to 175° F). A definite decrease of fanflow noise (roaring) should be noticed. If not, replacethe defective viscous fan drive unit.AUXILIARY ELECTRIC COOLING FANELECTRIC COOLING FAN AND RELAYDIAGNOSISNOTE: Refer to Electrical Group 8W for electriccooling fan and relay circuit schematic. The powertrain control module (PCM) will enter adiagnostic trouble code (DTC) in memory if it detectsa problem in the auxiliary cooling fan relay or circuit. Fig. 14 Radiator Pressure CapRefer to Group 25, Emission Control Systems for cor- There is no need to remove the radiator caprect DTC retrieval procedures. except for the following purposes: If the electric cooling fan is inoperative, check fuse (1) To check and adjust antifreeze freeze point.#11 (20A) in junction block and fuse #5 (40A maxi- (2) To refill system with new antifreeze.fuse) in the Power Distribution Center (PDC) with a (3) For conducting service procedures.12 volt test lamp or DVOM. If fuses are o.k., refer to (4) When checking for vacuum leaks.Group 8W for electric cooling fan and relay circuitschematic. WARNING: IF VEHICLE HAS BEEN RUN RECENTLY, WAIT AT LEAST 15 MINUTES BEFORERADIATOR CAP-TO-FILLER NECK SEAL— REMOVING RADIATOR CAP. WITH A RAG,PRESSURE RELIEF CHECK SQUEEZE RADIATOR UPPER HOSE TO CHECK IF With radiator cap installed on filler neck, remove SYSTEM IS UNDER PRESSURE. PLACE A RAGcoolant reserve/ overflow tank hose from nipple on OVER THE CAP AND WITHOUT PUSHING DOWN,filler neck. Connect a hand operated vacuum pump ROTATE CAP COUNTER-CLOCKWISE TO THEto nipple. Operate pump until a reading of 47-to-61 FIRST STOP. ALLOW FLUID TO ESCAPE THROUGHkPa (14- to-18 in. Hg) appears on gauge. If the read- OVERFLOW HOSE INTO COOLANT RESERVE/ing stays steady, or drops slightly and then remains OVERFLOW TANK. SQUEEZE RADIATOR UPPERsteady, the pressure valve seal is good. Replace radi- HOSE TO DETERMINE WHEN PRESSURE HASator cap if reading does not hold. BEEN RELEASED. WHEN COOLANT AND STEAM STOP BEING PUSHED INTO TANK AND SYSTEMWARNING: THE WARNING WORDS -DO NOT OPEN PRESSURE DROPS, REMOVE RADIATOR CAPHOT- ON THE RADIATOR PRESSURE CAP (Fig. 14) COMPLETELY.ARE A SAFETY PRECAUTION. WHEN HOT, PRES-SURE BUILDS UP IN COOLING SYSTEM. TO PRE-VENT SCALDING OR INJURY, THE RADIATOR CAP