105931-4151 ZEXEL 9 420 612 966 BOSCH GOVERNOR 9420612966 1059314151

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 are not filling the cooling system correctly, and combustion gas leaking into the system. Combustion gas can get into the system through inside cracks or bad cylinder head gaskets. Air in the cooling system causes a reduction in coolant flow and bubbles in the coolant. Air bubbles hold coolant away from engine parts, preventing heat flow.Air in the cooling system can be found by the Bottle Test. The equipment needed to make this test is a one pint bottle, a bucket of water, and a hose which will fit the end of the overflow pipe of the radiator.Before testing, make sure the cooling system is filled correctly. Use a wire to hold the relief valve in the radiator cap open. Install the radiator cap and tighten it. Put the hose over the end of the overflow pipe.Start the engine and operate it at high idle rpm for a minimum of five minutes after the engine is at normal operating temperature. Use a cover on the radiator core to keep the engine at operating temperature. After five or more minutes at operating temperature, place the loose end of the hose in the bottle filled with water.