3126B Petroleum Engine Caterpillar

Illustration 1	g01117215
Cooling system schematic (A) Sea water circuit (B) Engine coolant flow circuit (1) Auxiliary water pump (2) Aftercooler core (3) Heat exchanger (4) Coolant recovery bottle (5) Cooling system expansion tank (6) Water temperature regulator (7) Shunt line (customer installed component) (8) Cylinder block and cylinder head (9) Turbocharger (10) Engine oil cooler (11) Water pump (12) Exhaust manifold

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 heat exchanger.

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, debris, and oil

   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, "Refill Capacities and Recommendations".

3. Check the coolant mixture of antifreeze, water, and conditioner. The mixture should be approximately 50% water and 50% antifreeze. If coolant conditioner is used, the concentration should be approximately three percent of the total mixture. Refer to Operation and Maintenance Manual, "Refill Capacities and Recommendations". If the coolant mixture is incorrect, drain the cooling system and flush the cooling system. Refill the cooling system with the correct mixture.

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 cooling system if any of the following conditions exist: cracked cylinder liner, leaking seals, damaged cylinder head and cylinder head gasket leakage. 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. The following procedure can be used to purge air from the cooling system.

   1. Fill the cooling system. Avoid filling the cooling system faster than 19 liters per minute.

   2. Allow the filled cooling system to become level.

   3. Remove the pressure cap and start the engine. Run the engine at low idle for two minutes.

   4. Recheck the coolant level. Add coolant in order to fill the system, as needed.

   5. Run the engine at low idle for 2 minutes while the pressure cap is removed. Then, slowly run the engine up to high idle. Run the engine at high idle for 2 minutes in order to reach a normal operating temperature.

   6. Again, recheck the coolant level. As needed, add coolant in order to fill the system.

   7. Repeat steps 4.e and 4.f until no air is visible in the cooling system.

      Note: This engine is equipped with a water cooled turbocharger. Special care must be taken in order to remove the air from the turbocharger. If air is trapped in the turbocharger, a hot spot will be created. A hot spot could cause turbocharger failure.

   8. It may be necessary to open the vent lines for coolant from the turbocharger in order to purge the air from the entire cooling system. Slightly open the vent lines and start the engine at low idle. Run the engine at low idle until coolant begins to flow from the lines. Tighten the vent lines.

   9. Reinstall the cooling system pressure cap.

5. Check the engine's coolant temperature gauge. A coolant temperature gauge which does not operate 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 coolant recovery system. Coolant must flow freely to the recovery bottle during the engine's warm up cycle and coolant must flow back to the expansion tank during the engine's cool down cycle. Check the hose that connects the recovery bottle to the expansion tank. The hose must not leak and the hose must not draw in air. If either of these conditions exist, the system will not function properly.

8. Check the system's pressure cap. A pressure drop in the cooling system can cause the boiling point to be lowered. This can cause the cooling system to boil during engine operation. Refer to Testing and Adjusting, "Cooling System - Test".

9. Check the cooling system hoses and clamps. Damaged hoses that leak 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 engine 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 (Dual 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.

    4. Make any necessary repairs to the air inlet system.

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 engine's cooling air inlet.

12. Check the shunt line. 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 engine 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/sea water pump. An engine water pump with a damaged impeller does not pump enough coolant for correct engine cooling. A raw/sea water 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 core 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 Core - 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.