C12 Marine Engine Caterpillar

Illustration 1	g00861782
Cooling system schematic (A) Sea water (B) Jacket water (C) Air flow (1) Sea water pump (2) Aftercooler (3) Heat exchanger (4) Marine gear oil cooler (5) Water cooled exhaust (6) Fuel cooler (7) Air inlet (8) Return water manifold (9) Air outlet (10) Water cooled exhaust manifold (11) Engine block (12) Engine oil cooler (13) Engine water pump

Above normal coolant temperatures can be caused by many conditions. Use the following procedure to determine the cause of above normal coolant temperatures:

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Personal injury can result from escaping fluid under pressure. If a pressure indication is shown on the indicator, push the release valve in order to relieve pressure before removing any hose from the radiator.

1. Check the coolant level in the cooling system. Refer to Operation and Maintenance Manual, "Cooling System Coolant Level - Check". 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 and bubbles in the coolant. Air bubbles cause a reduction in the cooling of engine parts.

2. Check the quality of the coolant. The coolant should have the following properties:
   • Color that is similar to new coolant

   • Odor that is similar to new coolant

   • Free from dirt and debris

   If the coolant does not have these properties, drain the system and flush the system. Refill the cooling system with the correct mixture of water, antifreeze, and coolant conditioner. Refer to Operation and Maintenance Manual, "General Coolant Information".

3. Check the coolant mixture of antifreeze and water. The mixture should be approximately 50 percent water and 50 percent antifreeze. Refer to Operation and Maintenance Manual, "General Coolant Information". If the coolant mixture is incorrect, drain the cooling system and flush the cooling system. Refill the cooling system with the correct mixture of water and antifreeze.

4. Check for air in the cooling system. Air can enter the cooling system in different ways. The following items are some of the most common causes for air in the cooling system:
   • Filling the cooling system incorrectly

   • Combustion gas leakage into the cooling system

   • Loose hose clamp

   Combustion gas can get into the system through the following conditions: inside cracks, damaged cylinder head and damaged cylinder head gasket. A loose hose clamp can allow air into the cooling system during the cooldown period. Air in the cooling system causes a reduction in the cooling capacity of the coolant.

5. Check the water temperature gauge. A water temperature gauge which does not work correctly will not show the correct temperature. Refer to Testing and Adjusting, "Cooling System - Test".

6. Check the sending unit. In some conditions, the temperature sensor in the engine sends signals to a sending unit. The sending unit converts these signals to an electrical impulse which is used by a mounted gauge. If the sending unit malfunctions, the gauge can show an incorrect reading. Also if the electric wire breaks or if the electric wire shorts out, the gauge can show an incorrect reading.

7. Check the heat exchanger. The condition of the sea water that is circulated through the heat exchanger and the amount of operating time of the vessel can decrease the effectiveness of the heat exchanger. Operating in water that contains the following types of debris will adversely affect the heat exchanger system: silt, sediment, salt and algae. In addition, intermittent use of the vessel will adversely affect the heat exchanger system. Refer to Operation and Maintenance Manual, "Heat Exchanger - Inspect".

8. Check the filler cap. A pressure drop in the cooling system can cause the boiling point to be lower. This can cause the cooling system to boil. Refer to Testing and Adjusting, "Cooling System - Test".

9. 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 can become soft. Also, hoses can get cracks after a period of time. The inside of a hose can deteriorate, and the loose particles of the hose can cause a restriction of the coolant flow. Refer to Operation and Maintenance Manual, "Hoses and Clamps - Inspect/Replace".

10. 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 can cause higher than normal temperatures in the cooling system. Refer to Testing and Adjusting, "Air Inlet and Exhaust System - Inspect".

    1. If the measured restriction is higher than the maximum permissible restriction, remove the foreign material from the engine air cleaner element or install a new engine air cleaner element. Refer to Operation and Maintenance Manual, "Engine Air Cleaner Element - Clean/Replace".

    2. Check the air inlet system for a restriction again.

    3. If the measured restriction is still higher than the maximum permissible restriction, check the air inlet piping for a restriction.

11. 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.

    1. Make a visual inspection of the exhaust system. Check for damage to exhaust piping. If no damage is found, check the exhaust system for a restriction. Refer to Testing and Adjusting, "Air Inlet and Exhaust System - Inspect".

    2. If the measured restriction is higher than the maximum permissible restriction, there is a restriction in the exhaust system. Repair the exhaust system, as required.

    3. Ensure that the exhaust gas is not being drawn into the cooling air inlet.

12. Check the shunt line. The shunt line must be submerged in the expansion tank. A restriction of the shunt line from the expansion tank to the engine water pump inlet will cause a reduction in water pump efficiency. A reduction in water pump efficiency will result in low coolant flow and overheating.

13. Check the water temperature regulator. A water temperature regulator that does not open, or a water temperature regulator that only opens part of the way can cause overheating. Refer to Testing and Adjusting, "Water Temperature Regulator - Test".

14. Check the engine water pump and check the raw/seawater pump. An engine water pump with a damaged impeller does not pump enough coolant for correct engine cooling. A raw/seawater pump with a damaged impeller does not pump enough sea water for correct engine cooling. Remove the water pump and check for damage to the impeller. Refer to Testing and Adjusting, "Water Pump - Test".

15. Check the aftercooler. A restriction of water flow through the aftercooler can cause overheating. Check for debris or deposits which would prevent the free flow of water through the aftercooler. Refer to Operation and Maintenance Manual, "Aftercooler - Clean/Test".

16. 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 also causes a reduction in coolant flow through the system. Decreased coolant flow during high input of fuel will cause above normal heating.