GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Monte Carlo 🢒 Engine 🢒 Engine Cooling 🢒 Thermostat Diagnosis

Thermostat Diagnosis Overheat, Boiling Poor Cooling

Step

Action

Value(s)

Yes

No

The J 24731 tempil stick is a pencil-like device that has a wax material containing certain chemicals which melt at a given temperature. Use the temperature sticks to determine a thermostat's operating temperature by rubbing 87°C (188°F) and 97°C (206°F) sticks on the coolant outlet. The marks made by the sticks should melt when coolant temperatures reach 87°C (188°F) and 97°C (206°F), respectively. These temperatures are the normal operating range of the thermostat.

1
  1. Remove the radiator cap. Refer to Pressure Cap Description .
  2. Rub a 97°C (206°F) J 24731 on the coolant outlet.
  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 Overheating .

Does the engine still overheat?

--

--

System OK

3
  1. Replace the thermostat. Refer to one of the following procedures:
  2. Check the system

Is the engine still overheating?

--

--

System OK

Thermostat Diagnosis Cold Engine, Slow Warm Up

Step

Action

Value(s)

Yes

No

The J 24731 tempil stick is a pencil-like device that has a wax material containing certain chemicals which melt at a given temperature. Use the temperature sticks to determine a thermostat's operating temperature by rubbing 87°C (188°F) and 97°C (206°F) sticks on the coolant outlet. The marks made by the sticks should melt when coolant temperatures reach 87°C (188°F) and 97°C (206°F), respectively. These temperatures are the normal operating range of the thermostat.

1
  1. Remove the radiator cap. Refer to Pressure Cap Description .
  2. Rub a 87°C (188°F) J 24731 on the coolant outlet.
  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 warm up properly?

--

--

System OK

3
  1. Replace the thermostat. Refer to one of the following procedures:
  2. Check the system.

Is the engine still overheating?

--

--

System OK