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Car Engine Overheating: Why It’s Happening and How to Fix It

Stephen Fogel
February 12, 2019

An overheating engine can be a nerve racking experience. In the best cases it can cause decreased fuel mileage or simply light up a dashboard warning for engine temperature. In the worst cases, it can cause smoke or even complete engine failure.

As soon as you think you might be experiencing an overheating engine, it's important to pull over and take stock of what's wrong. If you cannot pull over safely turn off the air conditioning and turn the heater on to maximum.

overheating car

Overheating car

How to know if your engine is overheating

An overheating vehicle may display one or more of the following symptoms:

  • A temperature gauge that is reading higher than normal and into the red
  • An illuminated check engine light and/or engine temperature warning light
  • White or black smoke from the exhaust pipe when accelerating
  • The air conditioning stops working
  • Poor fuel mileage may be experienced
  • Contaminants in the coolant reservoir
  • Coolant escaping from the coolant reservoir due to boiling over

Common reasons for an overheating car engine

There are many reasons your vehicle could be overheating, but the most common include a coolant leak, a bad radiator fan, or a failed thermostat. These factors can contribute to an overheating in different ways.

 

Note: In an emergency, to keep your vehicle operating until you're able to reach a nearby repair shop, you can turn the heater on to the highest setting to keep the engine from overheating while driving. The heater core can act as a secondary radiator, but temperatures inside the vehicle may become unbearable.

Coolant leak

Your vehicle cooling system's objective is to maintain an optimal operating temperature for the engine. It achieves this by circulating coolant through the engine where it absorbs heat, then the coolant is delivered to the radiator where the heat is removed from the coolant. When the system has a leak and the coolant level drops too low, it will be unable to remove heat from the engine, and it will start to overheat.

Solution: There are some ways to identify an obvious coolant leak issue - mainly you will see a message or warning light on in the dash. You may also notice a smell of coolant in and around the car, or observing fluid dripping onto the ground or other parts of the vehicle. However for less obvious leaks, the best option is to have a mechanic inspect your vehicle for a coolant leak diagnosis.

Bad radiator fan

The radiator fan sits in front of the engine and helps cool hot coolant in the radiator before it returns to the engine to help keep it at a safe temperature while operating. When this fan stops working correctly, the radiator will lose its ability to cool the engine and the vehicle can quickly overheat. This will tend to occur more often while driving in traffic and not at higher speeds.

Solution: In most cases, the solution to this problem will require a radiator fan motor replacement or to replace the radiator fan itself.

Failed thermostat

A engine coolant thermostat controls engine temperature by blocking coolant flow to the radiator until the engine reaches a predetermined temperature. Because of this, the engine can first warm up efficiently, and then begin to maintain a safe operating temperature once the thermostat opens and allows coolant to circulate.

When a thermostat fails, it can either stick open, or closed. In both cases you may find that the heater doesn't blow warm air into the passenger compartment. A thermostat that is stuck open makes it difficult for the engine to warm up and can cause it to run colder than normal. On some vehicles this will also illuminate the check engine light and set the diagnostic trouble code P0128. On the flip side, a thermostat that is stuck closed will cause the vehicle to overheat since it will block coolant from circulating and doing its job to keep the engine at a safe temperature.

Solution: The most likely solution in this case is to replace the thermostat.

More information on engine overheating

Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.