If general inspections of the cooling system are not made, engine temperatures will increase. This is a common reason for increased engine temperatures. Make a visual inspection of the cooling system before a test is made with test equipment.
Visual Inspection Of The Cooling System
- Check coolant level in the cooling system.
- Look for leaks in the system.
- Look for bent radiator fins. Make sure that there is no restriction in the air flow through the radiator.
- Inspect the drive belts for the fan.
- Check for damage to the fan blades.
- Look for air or combustion gas in the cooling system.
- Inspect the filler cap and the surface that seals the cap. This surface must be clean.
Testing The Cooling System
Remember that temperature and pressure work together. Check temperature and pressure when a diagnosis is made of a cooling system. Cooling system pressures will have an effect on cooling system temperatures. The chart displays this relation between pressure and temperature.
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| Illustration 1 | g00286266 |
Boiling point of water | |
Test Tools for Cooling System
| Tools Needed | Quantity | |
| 4C-6500 | Digital Thermometer | 1 |
| 8T-2700 | Blowby/Air Flow Indicator | 1 |
| 9S-8140 | Pressurizing Pump | 1 |
| 6V-3121 | Multitach | 1 |
The 4C-6500 Digital Thermometer is used to diagnose engine overheating problems. This 4C-6500 Digital Thermometer is also used to diagnose problems in an engine that has been overcooled. This group can be used to check temperatures in several different parts of the cooling system. Refer to Special Instruction SEHS8446 in order to find the testing procedure.
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| Illustration 2 | g00286269 |
8T-2700 Blowby/Air Flow Indicator | |
The 8T-2700 Blowby/Air Flow Indicator is used to check the air flow through the radiator core. This test procedure is in Special Instruction SEHS8712.
The 9U-7400 Multitach is used to check the fan speed. The testing procedure is in Special Instruction SEHS7807.
Checking Pressure Cap
9S-8140 Pressurizing Pump
One cause for a pressure loss in the cooling system can be from a bad seal on the radiator pressure cap.
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Pressurized System: Hot coolant can cause serious burns. To open the cooling system filler cap, stop the engine and wait until the cooling system components are cool. Loosen the cooling system pressure cap slowly in order to relieve the pressure. |
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After the engine is cool, loosen the pressure cap and allow the pressure out of the cooling system. Then remove the pressure cap.
Inspect the pressure cap carefully. Look for damage to the seal or to the sealing surface. Any foreign material or foreign deposits that accumulate on the following parts must be removed: cap, seal and sealing surface.
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| Illustration 3 | g00296067 |
Typical schematic of filler cap (1) Sealing surface of both filler cap and radiator | |
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| Illustration 4 | g00286369 |
9S-8140 Pressurizing Pump | |
The 9S-8140 Pressurizing Pump is used to pressure test the caps and the cooling system for leaks.
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Pressurized System: Hot coolant can cause serious burns. To open the cooling system filler cap, stop the engine and wait until the cooling system components are cool. Loosen the cooling system pressure cap slowly in order to relieve the pressure. |
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To check the pressure cap opening pressure, use the procedure that follows:
- Remove the pressure cap from the radiator.
- Put the pressure cap on the 9S-8140 Pressurizing Pump .
- Look at the gauge for the exact pressure that makes the pressure cap open.
- Compare the reading on the gauge with the correct opening pressure on the cap.
- If the pressure cap is bad, install a new pressure cap.
Testing The Radiator And The Cooling System For Leaks
9S-8140 Pressurizing Pump
Refer to the following procedure in order to test the radiator and the cooling system for leaks.
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Pressurized System: Hot coolant can cause serious burns. To open the cooling system filler cap, stop the engine and wait until the cooling system components are cool. Loosen the cooling system pressure cap slowly in order to relieve the pressure. |
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- Remove the pressure cap from the radiator.
- Make sure that the coolant is over the top of the radiator core.
- Put the 9S-8140 Pressurizing Pump on the radiator.
- Increase the pressure reading on the gauge to 20 kPa (3 psi) more than the pressure on the pressure cap.
- Check the radiator for outside leakage.
- Check all connections and hoses for the cooling system for outside leakage.
- There is no leakage in the system when the following signs are observed:
- There is no outside leakage.
- The pressure reading on the gauge does not change after five minutes.
- There is no outside leakage.
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| Illustration 5 | g00286369 |
9S-8140 Pressurizing Pump | |
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Personal injury can result from hot coolant, steam and alkali. At operating temperature, engine coolant is hot and under pressure. The radiator and all lines to heaters or the engine contain hot coolant or steam. Any contact can cause severe burns. Remove filler cap slowly to relieve pressure only when engine is stopped and radiator cap is cool enough to touch with your bare hand. Cooling System Conditioner contains alkali. Avoid contact with skin and eyes. |
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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 | g00580866 |
Front Of The Right Side Of The Cylinder Head (1) Sending unit for 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.
Use one of the following thermometers:
A temperature indicator of known accuracy can also be used to make this check.
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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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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.
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| Illustration 7 | g00300300 |
Water temperature gauge | |
| 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. Observe the distance that the regulator has opened.
Refer to the Specifications, "Water Temperature Regulator".
If the distance is less than the amount listed in the manual, replace the water temperature regulator.