407914-2070 ZEXEL 9 443 614 917 BOSCH CONTROL UNIT 9443614917 4079142070

Overheating
Possible Causes/Corrections
Low Coolant Level/If 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. Bad Temperature Gauge/A 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 8T470 Thermistor Thermometer Group. Dirty Radiator/Check 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 V-BELT TENSION CHART that is shown in Specification section of this Service Manual. Bad Hose(s)/Bad 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 Restriction/A 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 efficiency. The result will be low coolant flow and overheating. Shutters Not Opening Correctly/Check 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. Bad Water Temperature Regulators/A 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. Bad Water Pump/A 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 System/Air can get into the cooling system in different ways. The most common causes