Toyota
Dodge Durango
 Service Manual
Cooling System » Diagnosis and testing
Preliminary checks

ENGINE 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.
  • Increase engine speed for more air flow is recommended.

(1) TRAILER TOWING: Consult Trailer Towing section of owners manual.

Do not exceed limits.

(2) AIR CONDITIONING; ADD-ON OR AFTER MARKET: A maximum cooling package should have been ordered with vehicle if add-on or after market A/C is installed. If not, maximum cooling system components should be installed for model involved per manufacturer's specifications.

(3) RECENT SERVICE OR ACCIDENT REPAIR: Determine if any recent service has been performed on vehicle that may effect cooling system.

This may be:

  • Engine adjustments (incorrect timing)
  • Slipping engine accessory drive belt(s)
  • Brakes (possibly dragging)
  • Changed parts. Incorrect water pump, or pump rotating in wrong direction due to belt not correctly routed
  • Reconditioned radiator or cooling system refilling (possibly under filled or air trapped in system).

NOTE: If investigation reveals none of the previous items as a cause for an engine overheating complaint, refer to following Cooling System Diagnosis charts.

These charts are to be used as a quick-reference only. Refer to the group text for information.

COOLING SYSTEM DIAGNOSIS CHART

CONDITION POSSIBLE CAUSES CORRECTION
TEMPERATURE GAUGE READS LOW 1. Has a Diagnostic Trouble Code (DTC) been set indicating a stuck open thermostat?

2. Is the temperature sending unit connected?

3. Is the temperature gauge operating OK?

4. Coolant level low in cold ambient temperatures accompanied with poor heater performance.

5. Improper operation of internal heater doors or heater controls.

1. Refer to Group 25, Emission Systems for On-Board Diagnostics and DTC information. Replace thermostat if necessary.

2. Check the temperature sensor connector. Refer to Group 8E. Repair connector if necessary.

3. Check gauge operation. Refer to Group 8E. Repair as necessary.

4. Check coolant level in the coolant reserve/overflow tank and the radiator.

Inspect system for leaks. Repair leaks as necessary. Refer to the Coolant section of the manual text for WARNINGS and CAUTIONS associated with removing the radiator cap.

5. Inspect heater and repair as necessary. Refer to Group 24, Heating and Air Conditioning for procedures.

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.

2. Is the temperature gauge reading correctly?

3. Is the temperature warning illuminating unnecessarily?

4. Coolant low in coolant reserve/ overflow tank and radiator?

5. Pressure cap not installed tightly. If cap is loose, boiling point of coolant will be lowered. Also refer to the following Step 6.

6. Poor seals at the radiator cap.

7. Coolant level low in radiator but not in coolant reserve/overflow tank. This means the radiator is not drawing coolant from the coolant reserve/ overflow tank as the engine cools

8. Incorrect coolant concentration

9. Coolant not flowing through system

10. Radiator or A/C condenser fins are dirty or clogged.

11. Radiator core is corroded or plugged.

12. Aftermarket A/C installed without proper radiator.

13. Fuel or ignition system problems.

14. Dragging brakes.

15. Bug screen or cardboard is being used, reducing airflow.

16. Thermostat partially or completely shut.

17. Viscous fan drive not operating properly.

18. Cylinder head gasket leaking.

19. Heater core leaking.

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.

Refer to Possible Causes (2-20).

2. Check gauge. Refer to Group 8E.

Repair as necessary.

3. Check warning lamp operation. Refer to Group 8E. Repair as necessary

4. Check for coolant leaks and repair as necessary. Refer to Testing Cooling System for Leaks in this Group.

5. Tighten 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.

7. (a) Check condition of radiator cap and cap seals. Refer to Radiator Cap in this Group. Replace cap if necessary.

(b) Check condition of radiator filler neck. If neck is bent or 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 coolant reserve/overflow tank and tanks hoses for blockage. Repair as necessary.

8. Check coolant. Refer to Coolant section in this Group for correct coolant/water mixture ratio.

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 area of obstruction and repair as necessary.

10. Remove insects and debris. Refer to Radiator Cleaning in this Group.

11. Have radiator re-cored or replaced.

12. Install proper radiator.

13. Refer to Fuel and Ignition System Groups for diagnosis.

14. Check and correct as necessary.

Refer to Group 5, Brakes for correct procedures.

15. Remove bug screen or cardboard.

16. Check thermostat operation and replace as necessary. Refer to Thermostats in this Group.

17. Check fan drive operation and replace as necessary. Refer to Viscous Fan Drive in this Group.

18. Check for cylinder head gasket leaks. Refer to Cooling System-Testing For Leaks in this Group. For repair, refer to Group 9, Engines.

19. Check heater core for leaks. Refer to Group 24, Heating and Air Conditioning. Repair as necessary.

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.

2. Temperature gauge or engine mounted gauge sensor defective or shorted. Also, corroded or loose wiring in this circuit.

3. Gauge reading rises when vehicle is brought to a stop after heavy use (engine still running)

4. Gauge reading high after re-starting a warmed up (hot) engine.

5. Coolant level low in radiator (air will build up in the cooling system causing the thermostat to open late).

6. Cylinder head gasket leaking allowing exhaust gas to enter cooling system causing a thermostat to open late.

7. Water pump impeller loose on shaft.

8. Loose accessory drive belt. (water pump slipping)

9. Air leak on the suction side of the water pump allows air to build up in cooling system causing thermostat to open late.

1. A normal condition. No correction is necessary.

2. Check operation of gauge and repair if necessary. Refer to Group 8E, Instrument Panel and Gauges.

3. A normal condition. No correction is necessary. Gauge should return to normal range after vehicle is driven.

4. A normal condition. No correction is necessary. The gauge should return to normal range after a few minutes of engine operation.

5. Check and correct coolant leaks.

Refer to Cooling System-Testing for leaks in this group.

6. (a) Check for cylinder head gasket leaks. Refer to Cooling System-Testing for Leaks in this group.

(b) Check for coolant in the engine oil.

Inspect for white steam emitting from the exhaust system. Repair as necessary.

7. Check water pump and replace as necessary. Refer to water Pumps in this group.

8. Refer to Accessory Drive Belts in this group. Check and correct as necessary.

9. Locate leak and repair as necessary.

PRESSURE CAP IS BLOWING OFF STEAM AND/OR COOLANT TO COOLANT TANK.

TEMPERATURE GAUGE READING MAY BE ABOVE NORMAL BUT NOT HIGH.

COOLANT LEVEL MAY BE HIGH IN COOLANT RESERVE/OVERFLOW TANK

1. Pressure relief valve in radiator cap is defective. 1. Check condition of radiator cap and cap seals. Refer to Radiator Caps in this group. 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. Refer to Cooling System- Testing For Leaks in this group.
DETONATION OR PRE-IGNITION (NOT CAUSED BY IGNITION SYSTEM). GAUGE MAY OR MAY NOT BE READING HIGH 1. Engine overheating.

2. Freeze point of coolant not correct.

Mixture is too rich or too lean.

1. Check reason for overheating and repair as necessary.

2. Check coolant concentration. Refer to the Coolant section of this group 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.

Refer to Radiator Cap in this group.

Replace if necessary

(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.

2. Fan blades striking a surrounding object.

3. Air obstructions at radiator or air conditioning condenser.

4. Thermal viscous fan drive has defective bearing.

5. A certain amount of fan noise may be evident on models equipped with a thermal viscous fan drive. Some of this noise is normal.

1. Replace fan blade assembly. Refer to Cooling System Fans in this Group

2. Locate point of fan blade contact and repair as necessary.

3. Remove obstructions and/or clean debris or insects from radiator or A/C condenser.

4. Replace fan drive. Bearing is not serviceable. Refer to Viscous Fan Drive in this group.

5. Refer to Viscous Fan Drive in this group for an explanation of normal fan noise.

INADEQUATE HEATER PERFORMANCE.

THERMOSTAT FAILED IN OPEN POSITION

1. Has a Diagnostic trouble Code (DTC) been set?

2. Coolant level low

3. Obstructions in heater hose/fittings

4. Heater hose kinked

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.

1. Refer to Group 25, Emissions for correct procedures and replace thermostat if necessary

2. Refer to Cooling System-Testing For Leaks in this group.

3. Remove heater hoses at both ends and check for obstructions

4. Locate kinked area and repair as necessary

5. Refer to Water Pump in this group. If a slipping belt is detected, refer to Accessory Drive Belts in this group. If heater core obstruction is detected, refer to Group 24, Heating and Air Conditioning.

STEAM IS COMING FROM THE FRONT OF VEHICLE NEAR THE GRILL 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 will evaporate when the thermostat opens. This opening allows heated water into the radiator. When the moisture contacts the hot radiator, 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. Refer to Coolant in this group for coolant concentration information. Adjust coolant mixture as necessary.
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.
    More about «Diagnosis and testing»:

    On-board diagnostics (obd)

    Preliminary checks

    Electric cooling fan

    Radiator coolant flow check

    Cooling system-testing for leaks

    Viscous fan drive

    Accessory drive belt diagnosis

    Thermostat-gas engines

    Radiator cap-to-filler neck seal-pressure relief check

    Radiator cap-pressure testing

    Coolant-low level aeration

    Cooling system-deaeration

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