LINK G 0319183 - Caterpillar

Pressurized System: Hot coolant can cause serious burns. To open the cooling system filler cap, stop the engine and wait until the cooling system components are cool. Loosen the cooling system pressure cap slowly in order to relieve the pressure.
Verify that the coolant is filled to the proper level. If the coolant level is too low, air will get into the cooling system. Air in the cooling system will cause a reduction in coolant flow.
Check the water pump. A water pump with a damaged impeller does not pump enough coolant. Remove the water pump and check for damage to the impeller.
Check the radiator or the heat exchanger for a restriction to coolant flow. Check internally for debris, dirt, or deposits on the radiator core. Debris, dirt, or deposits will restrict the flow of coolant through the radiator.
Check the cooling system hoses and clamps. Damaged hoses with leaks can normally be seen. Hoses that have no visual leaks can soften during operation. The soft areas of the hose can become kinked or crushed during operation. These areas of the hose can cause a restriction in the coolant flow. Hoses become soft and/or get cracks after a period of time. The inside of a hose can deteriorate, and the loose particles of the hose can restrict the coolant flow.
If the cooling system for this application is equipped with an expansion tank, check the shunt line for the expansion tank. The shunt line must be submerged in the expansion tank. A restriction of the shunt line from the expansion tank to the inlet of the jacket water pump will cause a reduction in water pump efficiency. A reduction in water pump efficiency will result in low coolant flow.
The engine may be running in the lug condition. When the load that is applied to the engine is too large, the engine will run in the lug condition. When the engine is running in the lug condition, engine rpm does not increase with an increase of fuel. This lower engine rpm causes a reduction in coolant flow through the system.Expected Result:A thorough inspection of the cooling system revealed a problem.Results:
OK - There is a problem with the cooling system.Repair: Repair the problem. Ensure that the repair eliminates the problem.STOP
Not OK - No problem was found with the cooling system.Repair: There may be a problem with the coolant flow switch. Refer to the diagnostic functional test Troubleshooting, "Coolant Flow Switch Circuit - Test".Ensure that any repairs eliminate the problem.STOP