For 1990-2009 cars

## Thermostat Diagnosis Cold Engine Slow Warm Up

### Tools Required

J 24731

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
The temperature stick is a pencil-like device that has a wax material containing chemicals which melt at a given temperature. Use the temperature sticks in order to determine a thermostat's operating temperature. Rub the following sticks on the thermostat housing:

• | The 87°C (188°F) J 24731

• | The 97°C (206°F) J 24731

The marks made by the sticks should melt when coolant temperatures reach the corresponding temperatures. These temperatures are the normal operating range of the thermostat.

1 |

1. Relieve the pressure and remove the radiator cap. Refer to Cooling System Draining and Filling .
2. Rub a 97°C (206°F) J 24731 .
3. Warm up the engine at fast idle.
4. Check for coolant flow before the mark begins to melt.

Is there coolant flow before the mark melts?

--

Go to Step 2

Go to Step 3

2 | The problem is caused from something other than the thermostat. Refer to Engine Fails To Reach Normal Operating Temperature . Does the engine still overheat? | -- | -- | System OK
3 |

1. Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .
2. Check the system.

Is the engine still overheating?

--

--

System OK

## Thermostat Diagnosis Overheat, Boiling Poor Heating

### Tools Required

J 24731

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
The temperature stick is a pencil-like device that has a wax material containing chemicals which melt at a given temperature. Use the temperature sticks in order to determine a thermostat's operating temperature. Rub the following sticks on the thermostat housing:

• | The 87°C (188°F) J 24731

• | The 97°C (206°F) J 24731

1 |

1. Relieve the pressure and remove the radiator cap. Refer to Cooling System Draining and Filling .
2. Rub a 87°C (188°F) J 24731 .
3. Warm up the engine at fast idle.
4. Check for coolant flow before the mark begins to melt.

Is there coolant flow before the mark melts?

--

Go to Step 3

Go to Step 2

2 | The problem is caused from something other than the thermostat. Refer to Engine Fails To Reach Normal Operating Temperature . Does the engine warm up properly? | -- | -- | System OK
3 |

1. Replace the thermostat. Refer to Engine Coolant Thermostat Replacement .
2. Check the system.

Is the engine still overheating?

--

--

System OK