Lately while you drive the 15 minutes to work each morning, you find the heater isn't even taking the chill out of the air, much less producing any appreciable amount of heat. This is an indication that your thermostat is stuck in the open position.

Every time you have to drive more then a mile or so down the road, the car overheats. The radiator is full of coolant, but the temperature gauge just keeps on climbing until you see the red warning light on the dash board. This indicates your thermostat is stuck in the closed position.

Both situations require replacement of the thermostat to return you car and or heater to proper operation.

All in all, this isn't too hard of a project for the average back yard mechanic. Be sure you wait until the engine is completely cool before you start, or the potential for a serious burn or scalding will be present if the coolant is hot and under pressure.

The first step is to drain the water level in the cooling system down below the thermostat level. You don't need to remove all the coolant, just lower the level below the top of the engine.

Your radiator may or may not have a drain cock, if not, find the correct plug on the side of the engine that will allow you to drain the coolant into a clean pan. Save the coolant as it can be reinstalled when your done. If your not sure you have located the correct plug, consult a corresponding repair manual, or call the dealer that sold you the car. If you remove the wrong plug, you may drain engine oil rather then coolant.

The thermostat, in most instances, is located in the housing that is attached to the engine end of your top radiator hose. By removing the two or three bolts that attach the housing to the top of the engine, you can remove the housing. You will find the thermostat will likely be just sitting there, and can be picked right out.

Take extreme care when breaking loose the housing from the engine. Gasket sealer can be a strong adhesive, and the housing is made of cast aluminum or pot metal. By attempting to pry on it, you will likely crack it and render it useless.

Clean both surfaces of old gasket material, using a rag and solvent as a final wiping to assure a good dry surface for the new gasket and sealer. Avoid making your own gasket, the new thermostat will come with a proper gasket that is much less likely to leak.

When you place the new thermostat in the receptacle, make sure you don't put it in upside down. The heat sensing coils need to be toward the engine, as that is the source of heat you want to activate and open and close the thermostat. There may be directions stamped right into the thermostat as to which side is to go up or down.

Coat the now clean sealing surfaces with a good high temperature sealer. Attach the new gasket to the engine, making sure the bolt holes line up and that the gasket is properly centered. If your engine has studs with nuts, in place of the bolts, this chore will be much easier. Install the thermostat housing over the new gasket and thermostat, reinstalling the nuts or bolts as the case may be.

Follow the torque recommendations listed in your repair manual. Over tightening will result in the cast thermostat housing cracking or breaking and you will have to replace it.

This is the easiest and cheapest cure for the originally listed problems. If this doesn't provide you with proper heat, your heater core may be plugged. If your engine continues to overheat, you may have a head gasket problem.

Not to say a new thermostat will cure all problems, but for around $10 you can eliminate it from the more expensive possibilities.

Learn more about this author, Curtis Carper.
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