Thermostat Diagnosis. Cadillac DeVille 1998

GM Service Manual Online

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1998 🢒 DeVille 🢒 Engine 🢒 Engine Controls - 4.0L and 4.6L 🢒 Thermostat Diagnosis

Table 1:	Engine Overheat--Boiling--Poor Engine Cooling
Table 2:	Cold Engine--Slow Warm-up--Not Enough 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 the 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	Remove the radiator cap. Rub a 97°C (206°F) J 24731 on the thermostat housing. Warm up the engine at fast idle. 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. Does the engine still overheat?	--	Go to Engine Overheating	System OK
3	Replace the thermostat. Check the system. Does the engine still overheat?	--	Go to Engine Coolant Thermostat Replacement	System OK

Cold Engine--Slow Warm-up--Not Enough 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 the 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 on the table, the thermostat may be worn.
1	Remove the radiator cap. Rub a 87°C (188°F) J 24731 on the thermostat housing. Warm up the engine at fast idle. 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. Does the engine warm up properly?	--	System OK	--
3	Replace the thermostat. Refer to Engine Coolant Thermostat Replacement . Check the system. Does the engine still fail to reach normal operating temperature?	--	--	System OK