Sometimes the thermostat will stick and prevent proper operation. If it sticks closed, the engine will overheat possibly causing severe engine damage. When this happens you will usually find the radiator at normal temperature while the engine is severely overheated. If the thermostat sticks open, you will find that the engine will not heat up quickly enough on cooler days. Your heater will also take longer to get the passenger compartment warm.

Changing a thermostat is a simple procedure, just follow these six steps:

1. Drain enough coolant to bring the level down below the level of the upper hose. The coolant can be saved and reused if it's not too old.


2. Remove the thermostat housing bolts. Tap the housing lightly to break the gasket seal and lift the housing off. Note the position of the thermostat.


3. Remove the thermostat and stuff a clean rag in the opening to prevent contamination. Scrape the old gasket off the engine and thermostat housing.


4. Thermostats sometimes stick closed when they're new. "Exercising" the new thermostat will help prevent this.


5. Insert the new thermostat with the spring end pointing down. Use a new gasket and gasket sealer.


6. Replace the thermostat housing and tighten the bolts evenly. Refill the system with coolant, bring the engine to operating temperature, and check for leaks.