Cooling System Overheating

Establish what driving conditions caused the complaint. Abnormal loads on the cooling system such as the following may be the cause:

• Prolonged idle.
• Very high ambient temperature.
• Slight tail wind at idle.
• Slow traffic.
• Traffic jams.
• High speed or steep grades.

Driving techniques that avoid overheating are:

• Idle with A/C off when temperature gauge is at end of normal range.

Recent Service Or Accident Repair:

• Engine adjustments (incorrect timing).
• Slipping accessory drive belt.
• Brakes (possibly dragging).
• Changed parts (incorrect water pump).
• Reconditioned radiator or cooling system refilling (possibly under filled or air trapped in system).

Trailer Towing:

Consult Trailer Towing section of owners manual. Do not exceed limits.

These charts are to be used as a quick-reference only.

CONDITION	POSSIBLE CAUSES	CORRECTION
TEMPERATURE GAUGE READS LOW	1. Has a DTC been set indicating a stuck open thermostat?	1. Replace thermostat if necessary. Refer to FOR ENGINE CJRA - REMOVAL AND INSTALLATION , FOR ENGINE CGVA - REMOVAL AND INSTALLATION or FOR ENGINE CGUA - REMOVAL AND INSTALLATION .
	2. Is the temperature sending unit connected?	2. Check the temperature sensor connector. Repair connector if necessary. FOR ENGINE CJRA - REMOVAL AND INSTALLATION , FOR ENGINE CGVA - REMOVAL AND INSTALLATION or FOR ENGINE CGUA - REMOVAL AND INSTALLATION .
	3. Is the temperature gauge operating OK?	3. Check gauge operation. Repair as necessary.
	4. Coolant level low in cold ambient temperatures accompanied with poor heater performance.	4. Check coolant level in the coolant pressure bottle and the radiator. Inspect system for leaks. Repair leaks as necessary. 1.
	5. Improper operation of internal heater doors or heater controls.	5. Inspect heater and repair as necessary.
	6. Electric fan functioning when not required.	6. Inspect electric fan for proper operation. FOR ENGINE CJRA - REMOVAL AND INSTALLATION , FOR ENGINE CGVA - REMOVAL AND INSTALLATION or FOR ENGINE CGUA - REMOVAL AND INSTALLATION .
TEMPERATURE GAUGE READS HIGH OR THE COOLANT WARNING LAMP ILLUMINATES. COOLANT MAY OR MAY NOT BE LOST OR LEAKING FROM THE COOLING SYSTEM.	1. Trailer is being towed, a steep hill is being climbed, vehicle is operated in slow moving traffic, or engine is being idled with very high ambient (outside) temperatures and the air conditioning is on. Higher altitudes could aggravate these conditions.	1. This may be a temporary condition and repair is not necessary. Turn off the air conditioning and attempt to drive the vehicle without any of the previous conditions. Observe the temperature gauge. The gauge should return to the normal range. If the gauge does not return to the normal range, determine the cause for overheating and repair.
	2. Is the temperature gauge reading correctly?	2. Check gauge. Repair as necessary.
	3. Is the temperature warning illuminating unnecessarily?	3. Check warning lamp operation. Repair as necessary.
	4. Coolant low in coolant pressure bottle and radiator?	4. Check for coolant leaks and repair as necessary.
	5. Pressure cap not installed tightly. If cap is loose, boiling point of coolant will be lowered. Also refer to the following Step 6.	5. Tighten cap.
	6. Poor seals at the radiator cap.	6. (a) Check condition of cap and cap seals.
		(b) Check condition of radiator filler neck. If neck is bent or damaged, replace radiator.
	7. Coolant not flowing through system.	7. (a) Check condition of pressure bottle cap and cap seals.
		(b) Check condition of radiator vent nipple. If neck is damaged, replace radiator.
		(c) Check condition of the hose from the radiator to the coolant tank. It should fit tight at both ends without any kinks or tears. Replace hose if necessary.
		(d) Check pressure bottle/overflow tank and tanks hoses for blockage. Repair as necessary.
	8. Incorrect coolant concentration.	8. Check coolant concentration.
	9. Fan installed backwards on viscous drive.	9. Mount fan on drive correctly.
	10. Radiator or A/C condenser fins are dirty or clogged.	10. Remove insects and debris.
	11. Radiator core is corroded or plugged.	11. Replace radiator.
	12. Fuel or ignition system problems.	12. Refer to ENGINE MECHANICAL, FUEL INJECTION AND IGNITION  for diagnosis.
	13. Dragging brakes.	13. Check and correct as necessary.
	14. Bug screen or cardboard is being used, reducing airflow.	14. Remove bug screen or cardboard.
	15. Thermostat partially or completely shut.	15. Check thermostat operation and replace as necessary.
	16. Viscous fan drive not operating properly.	16. Check fan drive operation and replace as necessary.
	17. Cylinder head gasket leaking.	17. Check for cylinder head gasket leaks.
	18. Heater core leaking.	18. Check heater core for leaks.
	19. Electric fan not functioning.	19. Inspect electric fan for proper operation.
TEMPERATURE GAUGE READING IS INCONSISTENT (FLUCTUATES, CYCLES OR IS ERRATIC)	1. During cold weather operation, with the heater blower in the high position, the gauge reading may drop slightly.	1. A normal condition. No correction is necessary.
	2. Temperature gauge or engine mounted gauge sensor defective or shorted. Also, corroded or loose wiring in this circuit.	2. Check operation of gauge and repair if necessary.
	3. Gauge reading rises when vehicle is brought to a stop after heavy use (engine still running).	3. A normal condition. No correction is necessary. Gauge should return to normal range after vehicle is driven.
	4. Gauge reading high after re-starting a warmed up (hot) engine.	4. A normal condition. No correction is necessary. The gauge should return to normal range after a few minutes of engine operation.
	5. Coolant level low in cooling system (air will build up in the cooling system causing the thermostat to open late).	5. Check and correct coolant leaks.
	6. Cylinder head gasket leaking allowing exhaust gas to enter cooling system causing a thermostat to open late.	6. (a) Check for cylinder head gasket leaks. Refer to engine articles.
		(b) Check for coolant in the engine oil. Inspect for white steam emitting from the exhaust system. Repair as necessary.
	7. Water pump impeller loose on shaft.	7. Check water pump and replace as necessary.
	8. Loose accessory drive belt.	8. Check and correct as necessary.
	9. Air leak on the suction side of the water pump allows air to build up in cooling system causing thermostat to open late.	9. Locate leak and repair as necessary.
PRESSURE CAP IS BLOWING OFF STEAM OR COOLANT TO COOLANT RECOVERY CONTAINER. TEMPERATURE GAUGE READING MAY BE ABOVE NORMAL BUT NOT HIGH. COOLANT LEVEL MAY BE HIGH IN COOLANT RECOVERY CONTAINER.	1. Pressure relief valve in radiator pressure cap is defective.	1. Check condition of radiator cap and cap seals. Replace cap as necessary.
COOLANT LOSS TO THE GROUND WITHOUT PRESSURE CAP BLOWOFF. GAUGE READING HIGH OR HOT	1. Coolant leaks in radiator, cooling system hoses, water pump or engine.	1. Pressure test and repair as necessary.
DETONATION OR PRE-IGNITION (NOT CAUSED BY IGNITION SYSTEM). GAUGE MAY OR MAY NOT BE READING HIGH	1. Engine overheating.	1. Check reason for overheating and repair as necessary.
	2. Freeze point of coolant not correct. Mixture is too rich or too lean.	2. Check coolant concentration and adjust ratio as required.
HOSE OR HOSES COLLAPSE WHILE ENGINE IS RUNNING	1. Vacuum created in cooling system on engine cool-down is not being relieved through coolant reserve/overflow system.	1. (a) Radiator cap relief valve stuck.
		(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.
NOISY VISCOUS FAN/DRIVE	1. Fan blades loose.	1. Replace fan blade assembly.
	2. Fan blades striking a surrounding object.	2. Locate point of fan blade contact and repair as necessary.
	3. Air obstructions at radiator or air conditioning condenser.	3. Remove obstructions and/or clean debris or insects from radiator or A/C condenser.
	4. Thermal viscous fan drive has defective bearing.	4. Replace fan drive. Bearing is not serviceable.
INADEQUATE HEATER PERFORMANCE. THERMOSTAT FAILED IN OPEN POSITION	1. Has a DTC been set?	1. Replace thermostat if necessary.
	2. Coolant level low.	2. Add coolant as necessary.
	3. Obstructions in heater hose/fittings.	3. Remove heater hoses at both ends and check for obstructions.
	4. Heater hose kinked.	4. Locate kinked area and repair as necessary.
	5. Water pump is not pumping water to/through the heater core. When the engine is fully warmed up, both heater hoses should be hot to the touch. If only one of the hoses is hot, the water pump may not be operating correctly or the heater core may be plugged. Accessory drive belt may be slipping causing poor water pump operation.	5. If a slipping belt is detected, refer to FOR ENGINE CJRA - ENGINE ASSEMBLY , FOR ENGINE CGVA - ENGINE ASSEMBLY or FOR ENGINE CGUA - ENGINE ASSEMBLY
STEAM IS COMING FROM THE FRONT OF VEHICLE NEAR THE GRILLE AREA WHEN WEATHER IS WET, ENGINE IS WARMED UP AND RUNNING, AND VEHICLE IS STATIONARY. TEMPERATURE GAUGE IS IN NORMAL RANGE	1. During wet weather, moisture (snow, ice or rain condensation) on the radiator or condenser will evaporate when the thermostat opens. This opening allows heated water into the radiator. When the moisture contacts the hot radiator or condenser, steam may be emitted. This usually occurs in cold weather with no fan or airflow to blow it away.	1. Occasional steam emitting from this area is normal. No repair is necessary.
COOLANT COLOR	1. Coolant color is not necessarily an indication of adequate corrosion or temperature protection. Do not rely on coolant color for determining condition of coolant.	1. Adjust coolant mixture as necessary. Refer to FOR ENGINE CJRA - COOLING SYSTEM , FOR ENGINE CGVA - COOLING SYSTEMFOR ENGINE CGUA - COOLING SYSTEM
COOLANT LEVEL CHANGES IN COOLANT RESERVE/OVERFLOW TANK. TEMPERATURE GAUGE IS IN NORMAL RANGE	1. Level changes are to be expected as coolant volume fluctuates with engine temperature. If the level in the tank was between the FULL and ADD marks at normal operating temperature, the level should return to within that range after operation at elevated temperatures.	1. A normal condition. No repair is necessary.
FAN RUNS ALL THE TIME	1. Fan control sensors inoperative.	1. Check for DTCs. Verify sensor readings.
	2. Fan control solenoid stuck "on".	2. Check fan operation speeds. Refer to fan speed operation table.
	3. Fan control solenoid harness damaged.	3. Check for DTC 1499. Repair as required.
	4. Transmission temperature too high.	4. Check for transmission over temp DTC.
	5. Engine coolant temperature too high.	5. (a) Check coolant level. Correct level as required.
		(b) Thermostat stuck. Replace thermostat.
		(c) Water pump failed. Replace water pump.
		(d) Coolant flow restricted. Clean radiator.
		(e) Air flow over radiator obstructed. Remove obstruction.