Why would a bad thermostat cause my check engine light to come on?

By Fred Hules II

My mechanic tells me my car needs a thermostat to correct the check engine light being on.
How does a bad thermostat cause the check engine light to go on?

Fred Hules II

The thermostat is part of the cooling system for the engine on a car or truck. The engine cooling system consists of a radiator, hoses, water pump, coolant reservoir, coolant cap, antifreeze/coolant and thermostat. The engine thermostat performs the same function as the thermostat in your home. That is to maintain the desired temperature.

Your engine is designed to operate at a certain temperature. Today’s modern engines are the most efficient engines that we have had since the automobile first hit the road. Not only are the engines better at giving power in a small package, they typically travel further on a gallon of gasoline and put out very low harmful exhaust emissions.

Any time the check engine light is illuminated on a vehicle, that vehicle’s emissions are exceeding the federal standards. If a thermostat fails to control the operating temperature of the engine, especially not allowing the engine to warm up fast enough, the tailpipe emissions levels will be too high during the start-up of the engine. If the tailpipe emissions are too high, your engine is wasting fuel.

So if your mechanic tells you your thermostat needs replacing, have it done. You will be helping to keep our air clean and save yourself money on gasoline.

Editor’s Note: Mr. Hules is the owner of Tech 1 Auto in Peoria. He is an ASE Certified Master Auto Technician and recipient of the 2015 and 2017 NAPA/ASE Arizona Technician of the year award. Listen to Mr. Hules host Automotive Know How radio show 4 p.m. every Monday on 1100 KFNX.

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