Modern automotive cooling systems are robust, but they have to be. Even short periods of overheating can severely damage a modern engine, necessitating expensive repairs to internal engine components. Every part of your car's cooling system must be functioning correctly to ensure that your engine remains at its proper temperature. Not only does this help to keep your internal engine parts in good shape, but it also ensures that your car's efficiency and performance are not compromised. The thermostat is one of these critical components.
The Role of the Thermostat
Your engine thermostat serves the same general purpose as the thermostat in your home. Instead of controlling the airflow to rooms in your house, however, it controls the flow of coolant through your engine. Although your engine must stay below its maximum safe operating temperature, it is also crucial that it reaches that temperature in the first place. An engine that is running too cold will perform poorly and offer lower fuel efficiency. Cold engine oil is less effective as well, increasing the amount of wear on internal engine parts. The job of your thermostat is to prevent coolant flow into the engine until it warms up, allowing your engine oil to reach its correct operating temperature quickly.
Thermostat Failure Modes
Your car's thermostat can fail in one of two ways: open or closed. A thermostat that fails in the closed position will prevent coolant from entering the engine, while one that fails in the open position will always allow the flow of coolant. Thankfully, thermostats are designed to fail open in most cases. When your thermostat fails open, your engine may have difficulty reaching its full operating temperature. If you drive very conservatively (or it is frigid outside), then your engine may never reach full temperature. A thermostat that fails closed, however, will rapidly result in an overheating engine.
Symptoms of Thermostat Failure
While thermostats that fail closed produce immediate and obvious signs, open failures may be less apparent. If your temperature needle is never making it to average operating temperature, then this is a reasonably good indication that your thermostat is stuck open. Unfortunately, many modern vehicles use temperature gauges that are electronically controlled to reduce visible fluctuations. This can mean that small temperature fluctuations sometimes go unnoticed. If your engine is underheated, however, there are likely to be several drivability symptoms. In particular, you can expect your fuel economy to drop noticeably and your engine to perform worse. Eventually, a bad thermostat will trigger a check engine light on your dash.
Replacing A Failed Thermostat
Thermostat failures are relatively common, but they also tend to be relatively cheap. On most vehicles, replacing a thermostat requires only an hour or two of labor. The price of the part itself will vary between make and models, but it is rare for a thermostat to cost more than a few hundred dollars. Since this part is so critical to the proper functioning of your vehicle, a bad thermostat should always be replaced as soon as possible. An auto repair shop can usually do this job in an afternoon, allowing you to get your car back on the road in a day or less.