GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1998 🢒 Seville 🢒 Engine 🢒 Engine Cooling 🢒 Thermostat Diagnosis
Table 1: Engine Overheat--Boiling--Poor Engine Cooling
Table 2: Cold Engine--Slow Warm-up--Poor Heat

Engine Overheat--Boiling--Poor Engine Cooling

Step

Action

Value(s)

Yes

No

The temperature stick is a pencil-like device that has a wax material containing certain chemicals which melt at a given temperature. Use J 24731 temperature sticks to determine a thermostat's operating temperature by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing. 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. If the coolant flows as indicated in the table, the thermostat may be worn.

1
  1. Connect scan tool.
  2. Using the scan tool view engine coolant temperature.

Is engine temperature displaying correct temperature?

--

Go to Step 2

Go to Temperature Gauge Diagnosis

2
  1. Remove the pressure cap.
  2. Rub a 97°C (206°F) J 24731 on the thermostat housing.
  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 4

3

The problem is caused from something other than the thermostat.

Does the engine still overheat?

--

Go to Engine Overheat Diagnosis

System OK

4
  1. Replace the thermostat.
  2. Check the system.

Does the engine still overheat?

--

--

System OK

Cold Engine--Slow Warm-up--Poor Heat

Step

Action

Value(s)

Yes

No

The temperature stick is a pencil-like device that has a wax material containing certain chemicals which melt at a given temperature. Use J 24731 temperature sticks to determine a thermostat's operating temperature by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing. 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. If the coolant flows as indicated in the table, the thermostat may be worn.

1
  1. Connect scan tool.
  2. Using the scan tool view engine coolant temperature.

Is engine temperature displaying correct temperature?

--

Go to Step 2

Go to Temperature Gauge Diagnosis

2
  1. Remove the pressure cap.
  2. Rub a 97°C (206°F) J 24731 on the thermostat housing.
  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 4

3

The problem is caused from something other than the thermostat.

Does the engine still overheat?

--

Go to Engine Overheat Diagnosis

System OK

4
  1. Replace the thermostat.
  2. Check the system.

Does the engine still overheat?

--

--

System OK