Cooling System Diagnosis General
Caution: Do not remove the radiator cap while the cooling system is hot. Serious personal injury may result. Only remove the radiator cap from a cool engine.
Caution: Under pressure, the temperature of the solution in the radiator can be considerably higher, without boiling. Removing the radiator cap while the engine is hot (pressure is high), will cause the solution to boil instantaneously, with explosive force. The solution will spew out over the engine, fenders, and the person removing the cap. Serious bodily injury may result. Flammable antifreeze, such as alcohol, is not recommended for use at any time. Flammable antifreeze could cause a serious fire.
| • | The engine appears to be overheating, with or without coolant loss. Refer to Engine Overheating . |
| • | Loss of coolant. Refer to Loss of Coolant . |
| • | The engine fails to reach normal operating temperature. Refer to Engine Fails To Reach Normal Operating Temperature . |
Exhaust Leaks
- Drain only enough coolant so that the level is just above the top of the cylinder head. Refer to Draining and Filling Cooling System .
- Disconnect the radiator inlet (upper) hose. Refer to, .
- Remove the coolant thermostat. Refer to Thermostat Installation or Oil Cooler Hose/Pipe Replacement
- Remove the accessory drive belt. Refer to, in Engine Mechanical.
- Start the engine. Increase the engine speed (RPM) several times, while observing the coolant level. Any noticeable rise in the coolant level or the appearance of bubbles may show that exhaust gas is leaking into the cooling system.
Notice: Exhaust gasses may enter the cooling system through a leaking cylinder head gasket. Exhaust gasses combine with water to form acids. These acids are harmful to the cooling system and the engine.
Notice: Allowing the drive belt tensioner to snap into the free position may result in damage to the tensioner.
Noise
Cooling system noise can be caused by restrictions to coolant flow. This can cause the coolant to boil at some localized point. Symptoms usually appear after extended idling or driving.
- Possible symptoms are:
- Backflush the cooling system, then retest. Refer to Flushing .
- Use a mechanic's stethoscope to determine what areas are still affected.
- Disassemble suspect components for further inspection and cleaning, as necessary.
- Use the following diagnostic table in order to locate restrictions in the cooling system.
| • | The engine may make snapping or cracking noises. |
| • | The radiator hoses may expand or collapse. |
| • | The coolant heater hoses may vibrate or thump. |
| • | The coolant heater core may gurgle or surge. |
| • | The engine overheat lamp may or may not be illuminated. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | With the engine running and the radiator filler cap off, verify that the coolant is circulating in the radiator. Is the coolant circulating? | -- | ||
2 | Feel around the front of the radiator core. Cold spots mean a blockage. Are there cold spots? | -- | ||
3 | Remove the coolant outlet. Refer to Thermostat Replacement. Is the thermostat stuck closed or is the coolant outlet blocked? | -- | ||
4 |
Is the system OK now? | -- | System OK | |
5 | Install new parts as necessary. Is the system OK now? | -- | System OK | |
6 | Inspect the crossover passage at the front of the inlet manifold (the thermostat must be removed for access). Is this area clear? | -- | ||
7 |
Is there a blockage? | -- | ||
8 |
Does the cylinder head(s) require further inspection? | -- | ||
9 | Use a penlight to inspect the engine block for a clogged coolant passage. Has a blockage been found? | -- |
Cooling System Diagnosis Testing
Caution: Do not remove the radiator cap while the cooling system is hot. Serious personal injury may result. Only remove the radiator cap from a cool engine.
Notice: Exhaust gasses may enter the cooling system through a leaking cylinder head gasket. Exhaust gasses combine with water to form acids. These acids are harmful to the cooling system and the engine.
Cooling System Check
The following tests are checking for the normal operation of these cooling system components. If more detailed information or further testing is needed, refer to the cooling system diagnostic charts located in this service category. Refer to Engine Overheating or Loss of Coolant or Engine Fails To Reach Normal Operating Temperature .
Coolant Pump Test
- Bring the engine up to normal operating temperature.
- Squeeze the (upper) radiator inlet hose, while accelerating the engine speed. You should feel a pressure surge.
- Check for a plugged vent hole in the coolant pump.
Radiator Test
- Bring the engine up to normal operating temperature.
- Turn the engine OFF.
- Cold spots indicate there are clogged sections of the radiator core.
| • | The radiator should feel hot along the left side. |
| • | The radiator should feel warm along the right side. |
| • | There should be an even temperature rise from the right to the left. |
Thermostat Test
- Use a tempil stick in order to find the opening and the closing temperatures of the coolant thermostat.
- Replace the coolant thermostat if it does not operate properly between this temperature range.
| • | J 24731- 188 tempil stick melts at 87°C (188°F). The thermostat should begin to open. |
| • | J 24731- 2- 6 tempil stick melts at 97°C (206°F). The thermostat should be fully open. |
