41508 Mercury SCREW, (.250-20 x .500)

System Response:The ECM will log the event.Possible Performance Effect:
The engine is shutdown.Troubleshooting:There may be a problem with the engine.Test Step 1. Check the Engine's Cooling System
Verify that the cooling system 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 radiator. If the engine is equipped with a SCAC cooling system or a heat exchanger, check for a restriction to coolant flow in the system.
Check for debris or damage between the fins of the radiator core. Debris between the fins of the radiator core restricts air flow through the radiator core.
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 mixture of antifreeze and water. Ensure that the recommendations in the Operation and Maintenance Manual are followed.
Check the water temperature regulators. A water temperature regulator that does not open, or a water temperature regulator that only opens part of the way can cause overheating.
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.
If the cooling system for this application is equipped with a fan, check the operation of the fan. A fan that is not turning at the correct speed can cause improper air speed across the radiator core. The lack of proper air flow across the radiator core can cause the coolant not to cool to the proper temperature differential.
Check for air in the cooling system. Air can enter the cooling system in different ways. The most common causes of air in the cooling system are the incorrect filling of the cooling system and combustion gas leakage into the cooling system. Combustion gas can get into the system through inside cracks, a damaged cylinder head, or a damaged cylinder head gasket.
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 restrict 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.
If the cooling system for this application is equipped with an aftercooler, check the aftercooler. A restriction of air flow through the air to air aftercooler can cause overheating. Check for debris or deposits which would prevent the free flow of air through the aftercooler. Results:Continue to the next test step.Test Step 2. Check the Engine's Air Inlet and Exhaust Systems
Check for a restriction in the air inlet system. A restriction of the air that is coming into the engine can cause high cylinder temperatures. High cylinder temperatures cause higher than normal temperatures in the cooling system.
Check for a restriction in the exhaust system. A restriction of the air that is coming out of the engine can cause high cylinder temperatures. Results:Continue to the next test step.Test Step 3. Check for an Extreme Operating Environment
Consider high ambient temperatures. When ambient temperatures are too high for the rating of the cooling system, there is not enough of a temperature difference between the ambient air and coolant temperatures.
Consider high altitude operation. The cooling capability of the cooling system is reduced at higher altitudes. A pressurized cooling system that is large enough to keep the coolant from boiling must be used.
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 engine revealed a problem.Results:
OK - There is a problem with the engine.Repair: Repair the problem. Ensure that the repair eliminates the problem.STOP