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 coolant flow 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 or at the sight glass on the radiator top tank.
Defective 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 to hot but other conditions are normal, install a thermometer you know is correct and/or check the cooling system.
Dirty Radiator ... Check the radiator core for debris which prevents free air flow. 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 Belts ... Loose fan or water pump belts will cause a reduction in air or water flow. Tighten belts until a 25 lb. (11,3 kg) force at the half way point between the pulleys, moves the belts .875 ± .125 in. (22,0 ± 3,0 mm).
Defective Hoses ... Leaks in hoses can normally be seen. Hoses that have no visual leaks can collapse during operation and cause restriction in the flow of coolant. Hoses become soft and/or get cracks after a period of time. Change hoses after a year of use. The inside can become loose and the loose particles 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 over-heating.
Shutters Not Opening Correctly ... Check the opening temperature of the shutters. The shutters must be open at 200°F (93°C).
Defective Thermostats ... A thermostat that does not open or only opens part of the way can cause above normal heating. To test the thermostats, see the topic WATER TEMPERATURE THERMOSTAT.
Defective Water Pump* ... A water pump with a loose pulley or impeller does not pump enough coolant for correct engine cooling. A loose pulley or impeller can be found by removing the drive belt for the water pump and by pushing the pulley back and pulling it forward.
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. See the topic: AIR, GASES AND STEAM IN THE SYSTEM.
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 fan and shroud position are according to the recommendations of the truck manufacturer.
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.
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.
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.
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 be used.
Engine Used in a Lug Condition ... "Lugging" (when the truck is used in a gear too high for engine rpm to go up as accelerator pedal is pushed farther down, or when the truck is used in a gear where engine rpm goes down with accelerator pedal at maximum travel) the engine causes the engine rpm and fan rpm to be low. This low rpm causes a reduction in air flow through the radiator and a reduction in the flow of coolant through the system. This combination of less air and less coolant flow during high input of fuel will cause above normal heating.
Air Inlet Restriction ... Restriction of the air coming into the engine causes high cylinder temperatures and more than normal amount of heat to pass to the cooling system. Check the air inlet restriction.
Exhaust Restriction ... Restriction in the exhaust system causes high cylinder temperatures and more than normal amount of heat to pass to the cooling system. To see if there is an exhaust restriction, make a visual inspection of the exhaust system. Check for damage to piping or for a defective muffler. If no damage is found, check the system by removing the exhaust pipes from the exhaust manifolds. With the exhaust pipes removed, start and run the engine to see if the problem is corrected.
Fuel Injection Timing Not Correct. *
Transmission Problems ... Power shift or automatic transmissions that are cooled by the engine cooling system can cause above normal heating if they are out of adjustment or not working correctly. *
Long Idle Periods ... When the engine is running with no load, only a small quantity of fuel is being burned and engine heat is removed too fast.
Very Light Load ... Very light loads, and a very slow speed or downhill travel can cause below normal heating because of the low heat input of the engine. The installation of shutters helps to correct this condition.
Defective Thermostat(s) ... Thermostat(s) that are "stuck" open (will not move to the closed position) will cause below normal heating. A thermostat that is stuck between the open and closed positions or only opens part of the way can cause below normal heating when the truck has a light load.
*Authorized dealers are equipped with the necessary tools and personnel familiar with disassembly and assembly procedures to perform these services.