C12.9 Marine Propulsion Engine Caterpillar

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Making contact with a running engine can cause burns from hot parts and can cause injury from rotating parts. When working on an engine that is running, avoid contact with hot parts and rotating parts.

This engine has a pressurized cooling system. A pressurized cooling system has two advantages. The cooling system can be operated in a safe manner at a temperature higher than the normal boiling point (steam) of water.

This type of system prevents cavitation in the water pump. Cavitation is the forming of low-pressure bubbles in liquids that are caused by mechanical forces. It is more difficult to create an air pocket or a steam pocket with this type of cooling system.

Illustration 1	g00921815
Boiling point of water

Remember that temperature and pressure work together. When a diagnosis is made of a cooling system problem, temperature and pressure must be checked. Cooling system pressure will effect the cooling system temperature. For an example, refer to Illustration 1. This will show the effect of pressure on the boiling point (steam) of water. This will also show the effect of height above sea level.

The coolant level must be to the correct level to check the coolant system. The engine must be cold and the engine must not be running.

Note: At operating temperature, the engine coolant is hot and the coolant is under pressure. Use caution when you work on a hot engine.

After the engine is cool, loosen the pressure cap to relieve the pressure out of the cooling system. Then remove the pressure cap.

Maintain the coolant level within 26 mm (1 inch) of the bottom of the filler pipe.

Test Tools For Cooling System

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Making contact with a running engine can cause burns from hot parts and can cause injury from rotating parts. When working on an engine that is running, avoid contact with hot parts and rotating parts.

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4C-6500 Digital Thermometer

The 4C-6500 Digital Thermometer is used in the diagnosis of overheating conditions and in the diagnosis of overcooling conditions. This group can be used to check temperatures in several different parts of the cooling system. Refer to Operating Manual, NEHS0554, " 4C-6500 Digital Thermometer Group" for the testing procedure.

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9U-7400 Multitach

The 9U-7400 Multitach Tool Group is used to check the fan speed. Refer to Operating Manual, NEHS0605, " 9U-7400 Multitach Tool Group" for the testing procedure.

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9S-8140 Pressurizing Pump

The 9S-8140 Pressurizing Pump is used to test the pressure caps. This pressurizing pump is also used to pressure test the cooling system for leaks.

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1U-7297 Coolant/Battery Tester or 1U-7298 Coolant/Battery Tester

Check the coolant frequently in cold weather for the proper glycol concentration. Use either the 1U-7297 Coolant/Battery Tester or the 1U-7298 Coolant/Battery Tester to ensure adequate freeze protection. The testers are identical except for the temperature scale. The testers give immediate, accurate readings. The testers can be used for coolants that contain ethylene or propylene glycol.

Making the Correct Antifreeze Mixtures

Adding pure antifreeze as a makeup solution for the cooling system top-off is an unacceptable practice. Adding pure antifreeze increases the concentration of antifreeze in the cooling system. This increases the concentration of the dissolved solids and the undissolved chemical inhibitors in the cooling system. Add the coolant/water mixture to the same freeze protection as your cooling system. The following chart helps with determining the concentration of antifreeze to use. Refer to Operation and Maintenance Manual, "General Coolant Information".

Checking the Filler Cap

One cause for a pressure loss in the cooling system can be a damaged seal on the pressure cap.

Illustration 6	g01430877
Typical schematic of pressure cap (1) Sealing surface of both pressure cap and the heat exchanger

To check for the amount of pressure that opens the pressure cap, use the following procedure:

1. After the engine cools, carefully loosen the pressure cap. Slowly release the pressure from the cooling system. Then, remove the pressure cap.

   Carefully inspect the pressure cap. Look for any damage to the seals and to the sealing surface. Inspect the following components for any foreign substances:

   • Pressure cap

   • Seal

   • Surface for seal

   Remove any deposits that are found on these items.

2. Install the pressure cap on the 9S-8140 Pressurizing Pump.

3. Look at the gauge for the exact pressure that opens the pressure cap.

4. The opening pressure should be 100 kPa (14.5psi).

5. If the pressure cap is damaged, replace the pressure cap.

Testing The Expansion Tank And Cooling System For Leaks

Use the following procedure to check the cooling system for leaks:

1. After the engine is cool, loosen the pressure cap slowly and allow pressure out of the cooling system. Then remove the pressure cap from the expansion tank.

2. Ensure that the expansion tank is full of coolant.

3. Install the 9S-8140 Pressurizing Pump onto the expansion tank.

4. Take the pressure reading on the gauge to 20 kPa (3 psi) more than the pressure on the pressure cap. The pressure on a typical pressure cap is 48 kPa (7 psi) to 104 kPa (15 psi).

5. Check the heat exchanger for leakage on the outside.

6. Check all connection points for leakage, and check the hoses for leakage.

The cooling system does not have leakage only if the following conditions exist:

• You do NOT observe any outside leakage.

• The reading remains steady after five minutes.

Note: Check the engine oil for evidence of coolant leakage.

The inside of the engine cooling system has leakage only if the following conditions exist:

• The reading on the gauge goes down.

• You do NOT observe any outside leakage.

• Evidence of coolant on the engine oil gauge.

Make any repairs, as required.

Test For The Water Temperature Gauge

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Making contact with a running engine can cause burns from hot parts and can cause injury from rotating parts. When working on an engine that is running, avoid contact with hot parts and rotating parts.

Check the accuracy of the coolant temperature indicator or coolant temperature sensor if you find either of the following conditions:

• The engine runs at a temperature that is too hot, but a normal temperature is indicated. A loss of coolant is found.

• The engine runs at a normal temperature, but a hot temperature is indicated. No loss of coolant is found.

Coolant temperature can also be read on the display screens of the Caterpillar Electronic Technician (ET).

Remove the plug from port (1). Install one of the following thermometers in the open port:

• The 4C-6500 Digital Thermometer

• The 2F-7112 Thermometer

A temperature indicator of known accuracy can also be used to make this check.

Start the engine. Run the engine until the temperature reaches the desired range according to the test thermometer. The reading on the water temperature indicator should agree with the test thermometer within the tolerance range of the coolant temperature indicator.