This type of system prevents cavitation in the water pump. Cavitation is the low pressure bubbles that are made in liquids by mechanical forces. With this type of cooling system, an air pocket or a steam pocket becomes more difficult to create in the cooling system.
Visual Inspection Of The Cooling System
Cooling systems that are not regularly inspected are the cause for increased engine temperatures. Make a visual inspection of the cooling system before a test is made with test equipment.
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At operating temperature, the engine coolant is hot and under pressure. Steam can cause personal injury. Check the coolant level only after the engine has been stopped and the filler cap is cool enough to touch with the bare hand. Remove the filler cap slowly to relieve pressure. Cooling system conditioner contains alkali. Avoid contact with skin and eyes to prevent personal injury. |
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- Check the coolant level in the cooling system.
- Look for leaks in the system.
Note: The seals of the water pump will leak. A small amount of coolant leakage across the surface of the face type seals is normal. The leakage is required to provide lubrication for this type of seal. A hole is provided in the water pump housing. This hole allows the coolant to drain from the pump housing. Intermittent leakage of small amounts of coolant from this hole is not an indication of water pump seal failure. Replace the water pump seals only if a large amount of leakage or a constant flow of coolant is observed draining from the water pump housing.
- Look for leaks or restrictions in the expansion tank and raw water heat exchanger.
- Inspect the raw water pump and inspect the inlet screens.
- Check for damage or check for restrictions.
- Look for air or combustion gas in the cooling system.
- Inspect the filler cap, and check the surface that seals the filler cap. This surface must be clean.
Testing The Cooling System
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| Illustration 1 | g00286266 |
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 have an effect on the cooling system temperature. For an example, refer to the 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.
Test Tools For Cooling System
| Tools Needed | Quantity | |
| 4C-6500 | Digital Thermometer | 1 |
| 9S-8140 | Pressurizing Pump | 1 |
| 9U-7400 | Multitach | 1 |
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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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| Illustration 2 | g00300241 |
4C-6500 Digital Thermometer | |
The 4C-6500 Digital Thermometer is used in the diagnosis of overheating problems or in the diagnosis of overcooling problems. This group can be used to check temperatures in several different parts of the cooling system. Refer to the testing procedure in Operation and Maintenance Manual.
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| Illustration 3 | g00300249 |
9U-7400 Multitach | |
The 9U-7400 Multitach is used to check the fan speed.
The Multitach can measure engine rpm from a magnetic pickup. This magnetic pickup is located in the flywheel housing. The magnetic pickup also uses the ability to measure engine rpm from visual engine parts that are rotating. Refer to the testing procedure in Special Instruction, SEHS7807.
Checking the Filler Cap
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| Illustration 4 | g00286369 |
9S-8140 Pressurizing Pump | |
The 9S-8140 Pressurizing Pump is used to test the filler caps. This pressurizing pump is also used to pressure test the cooling system for leaks.
| Tools Needed | Quantity | |
| 9S-8140 | Pressurizing Pump | 1 |
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At operating temperature, the engine coolant is hot and under pressure. Steam can cause personal injury. Check the coolant level only after the engine has been stopped and the filler cap is cool enough to touch with the bare hand. Remove the filler cap slowly to relieve pressure. Cooling system conditioner contains alkali. Avoid contact with skin and eyes to prevent personal injury. |
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One cause for a pressure loss in the cooling system can be a defective seal on the expansion tank filler cap.
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| Illustration 5 | g00296067 |
Typical schematic of filler cap (1) Sealing surface of both filler cap and expansion tank | |
After the engine cools, loosen the filler cap. Slowly release the pressure from the cooling system. Then, remove the filler cap.
Carefully inspect the filler cap. Look for any damage to the seals and to the sealing surface. Inspect the following components for any foreign substances:
- filler cap
- seal
- surface for seal
Remove any deposits or material that are found on these items.
To check for the amount of pressure that opens the filler cap, use the following procedure:
- Carefully remove the filler cap from the expansion tank of the heat exchanger.
- Put the filler cap on the 9S-8140 Pressurizing Pump .
- Look at the gauge for the exact pressure that opens the filler cap.
- Compare the gauge's reading with the correct pressure that should open the filler cap:
Note: The correct pressure that makes the filler cap open is on the filler cap.
- If the filler cap is defective, replace the filler cap.
Test For The Water Temperature Gauge
| Tools Needed | Quantity | |
| 4C-6500 or 2F-7112 |
Digital Thermometer or Thermometer |
1 |
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| Illustration 6 | g00331990 |
The back of the left cylinder head (Sending unit for the water temperature gauge.) | |
Check the accuracy of the water temperature indicator or water 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.
Remove the plug (1). Install one of the following thermometers:
A temperature indicator of known accuracy can also be used to make this check.
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At operating temperature, the engine coolant is hot and under pressure. Steam can cause personal injury. Check the coolant level only after the engine has been stopped and the filler cap is cool enough to touch with the bare hand. Remove the filler cap slowly to relieve pressure. Cooling system conditioner contains alkali. Avoid contact with skin and eyes to prevent personal injury. |
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| Illustration 7 | g00300300 |
Water temperature gauge | |
Start the engine. Run the engine until the temperature reaches the desired range according to the test thermometer. If necessary, place a cover over part of the radiator in order to cause a restriction of the coolant flow. The reading on the water temperature indicator should agree with the test thermometer within the tolerance range of the water temperature indicator.
| Pointer Position |
Test Thermometer °C |
Test Thermometer °F |
| 1 | 65 to 77 | 150 to 170 |
| 2 | 99 to 103 | 210 to 218 |
Water Temperature Regulator Test
- Remove the regulator from the engine.
- Heat water in a pan until the temperature is 92°C (198°F). Stir the water in the pan. This allows the temperature to radiate throughout the pan.
- Hang the water temperature regulator in the pan of water. The water temperature regulator must be below the surface of the water. The water temperature regulator must be away from the sides and the bottom of the pan.
- Keep the water at the correct temperature for ten minutes.
- After ten minutes, remove the water temperature regulator. Immediately check the distance that the water temperature regulator has opened.
Refer to the Specifications, "Water Temperature Regulator" for more information about the minimum distance for openings on the water temperature regulator.
If the distance is less than the amount listed in the manual, replace the water temperature regulator.