0312241 JOHNSON SCREW

Above Normal Heating
Recommended Procedure
1. 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.2. 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 8T0470 Thermistor Thermometer Group.3. 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.4. Loose Belt(s) ... Loose fan belts will cause a reduction in air flow. Tighten the belts according to V-Belt Tension Chart that is shown in Specification section of this Service Manual.5. 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 of a hose can deterioriate, and the loose particles of the hose can cause a restriction in the flow of coolant.6. Shunt Line Restriction ... A restriction of the shunt line from the radiator top tank to the engine water pump inlet, or a shunt line not installed correctly, will cause a reduction in water pump efficiency. The result will be low coolant flow and overheating.7. 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.8. Bad Water Temperature Regulator(s) ... 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.9. Bad Water Pump ... A water pump with a loose or damaged impeller does not pump enough coolant for correct engine cooling. Remove the water pump and check for damage to the impeller. If the impeller has no damage, check the impeller clearance. The clearance between the impeller and the housing is 0.28 to 0.84 mm (.011 to .033 in).10. 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. Put the bottle in the bucket of water with the top down. If the water gets out of the bottle in less than forty seconds, there is too much exhaust gas leakage into the cooling system. Find the cause of the air or gas getting into the cooling system and correct as necessary.11. Wrong Fan, Fan or Shroud Not in Correct Position ... A wrong fan, or a fan or shroud in a wrong position will cause a reduction or a loss of air flow through the radiator. The fan must be large enough to send air through most of the area of the radiator core. Make sure the fan size, fan shroud and position of fan and shroud are according to the recommendations of the Truck Manufacturer.12. Radiator Too Small ... A radiator which is too small does not have enough area to release the heat to the cooling air. This will cause the engine to run at higher than normal temperatures. Make sure the radiator size is according to the recommendations of the Truck Manufacturer.13. Not Enough Air Flow Through Radiator Because of Restriction in Engine Compartment ... The air flow through the radiator comes out of the engine compartment. Make sure the filters, air conditioners and similar items are not installed in a way which prevents free flow of air into and out of the engine compartment.14. High Outside Temperature ... When outside temperatures are too high for the rating of the cooling system, there is not enough temperature difference between the outside air and coolant temperatures. To get better cooling, use the truck in a lower gear.15. Operation at High Altitude ... The cooling capacity of the cooling system goes down as the truck is used at higher altitudes. A system, under pressure, large enough to keep the coolant from boiling must