4 Symptoms of a bad Coolant Temperature Sensor in Your Car

Last Updated on May 12, 2019 by themechanic

Inside of almost every vehicle is a small sensor in the engine. This part, called a coolant temperature sensor, is responsible for measuring how hot the coolant is getting. When this part malfunctions, it can spell trouble for your car or truck. If you suspect there is a problem with your car’s coolant temperature sensor, here are 4 classic signs of the problem.

1) A dip in fuel economy

When the coolant temperature sensor malfunctions, the first sign isn’t necessarily a dramatic one. You may notice instead that a tank of gas doesn’t go quite as far as it used to. This is because the temperature of the engine determines how much gas is injected at one time. When the coolant temperature sensor isn’t working, the engine acts as if it is cold all the time, using more gas than is necessary.
There are a lot of car problems that can also cause poor fuel efficiency, so if this is your only symptom you’ll need to do more sleuthing to make sure this is really the issue.

2) Black smoke pouring from the engine

When you start up your car, the normal color of exhaust coming from the pipe should be clear or a thin white, depending on the weather. If black smoke is erupting from the tail pipe instead, this is not typically a normal color.
The reason why this happens is also due to the car thinking that the engine is still cold. Because of this, it gives the engine more gas than it actually needs. With excess fuel in the combustion chamber, not all of it is burned, leading to some of the gas getting burned in the exhaust pipe. This leads to the black smoke you see.

3) The engine may overheat

Sometimes the sensor doesn’t send a signal saying the engine is too cold, but rather too hot. In this case, the engine compensates for a hot engine when it isn’t actually so. When this happens, the engine may misfire, or the engine may overheat.

4) Check Engine Light comes on

Last but not least, if the engine detects something is wrong, the check engine light will come on.

While none of these symptoms on their own can diagnose a faulty coolant temperature sensor, if you see some of these symptoms working together you may want to check the sensor. Reading the codes on your car is a good first step, and so is checking something simpler such as the level of the coolant. The sensor needs to be fully submerged in coolant fluid to be effective, and if the coolant is low, it could cause symptoms that appear similar.

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Replacing the coolant temperature sensor varies in difficulty depending on the make and model of the car. If you’re not confident in your ability to repair the car yourself, it is best to have a trained professional do it, as the car will not function properly without the sensor.

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