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Overheating
Possible Causes/Corrections Low Coolant LevelIf the coolant level is too low, not enough coolant will go through the engine and radiator. This lack of coolant will not take enough heat from the engine and there will not be enough flow of coolant through the radiator to release the heat into the cooling air. Low coolant level is caused by leaks or wrong filling of the radiator. With the engine cool, be sure that coolant can be seen at the low end of the fill neck on the radiator top tank. Defective Temperature GaugeA temperature gauge which does not work correctly will not show the correct temperature. If the temperature gauge shows that the coolant temperature is too hot but other conditions are normal, either install a gauge you know is good or check the cooling system with the 4C6500 Digital Thermometer Group. Dirty RadiatorCheck the radiator for debris between the fins of the radiator core which prevents free air flow through the radiator core. Check the radiator for debris, dirt, or deposits on the inside of the radiator core which prevents free flow of coolant through the radiator. Loose Belt(s)Loose fan or water pump belts will cause a reduction in air or water flow. Tighten the belts according to Belt Tension Chart that is shown in Specification Section of this Service Manual. Defective Hose(s)Defective hoses with leaks can normally be seen. Hoses that have no visual leaks can "collapse" (pull together) during operation and cause a restriction in the flow of coolant. Hoses become soft and/or get cracks after a period of time. Hoses must be changed after 50,000 miles or a year of use. The inside can become loose, and the loose particles of the hose can cause a restriction in the flow of coolant. Shunt Line RestrictionA restriction of the shunt line from the radiator top tank to the engine front cover, or a shunt line not installed correctly, will cause a reduction in water pump efficientcy. The result will be low coolant flow and overheating. Shutters Not Opening CorrectlyCheck the opening temperature of the shutters. The shutters must be completely closed at a temperature below the fully open temperature of the water temperature regulators. Also, verify that fan control switches or viscous fans are operating correctly. Defective Water Temperature RegulatorsA regulator that does not open, or only opens part of the way, can cause above normal heating. To test the thermostats, see the Testing and Adjusting Section of this Service Manual. Defective Water PumpA water pump with a loose impeller does not pump enough coolant for correct engine cooling. A loose impeller can be found by removing the water pump, and by pushing the shaft back and pulling it forward. If the impeller has no damage, check the impeller clearance. The clearance between the impeller and the housing is 0.56 to 1.50 mm (.022 to .059 in). Air In Cooling SystemAir can get into the cooling system in different ways. The most common causes are