Why is my car overheating when it has coolant?

My wife’s car overheated yesterday, and I insisted she must be low on coolant, but when I checked, the coolant levels were fine. Boy, did I feel foolish! We live in Maine, so it’s certainly not scorching outside. How can a car overheat if it has coolant?

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Answer provided by
Laura Salvas
Answered on Apr 21, 2022
There’s no worse feeling than being wrong even when your logic was totally right! You’re correct that loss of coolant is a common cause of overheating and that the mild Maine weather likely played no part in this, but if your coolant isn’t circulating properly, then it won’t cool down your car.
If your car is overheating, but it has coolant, these are some possible reasons:
  • Bad water pump. The water pump keeps the coolant circulating through the engine, so if it stops working your coolant won’t circulate and can reach boiling temperatures.
  • Clogged radiator. After it passes through the engine, coolant cools down as it passes through the radiator. But if your radiator is clogged, coolant can’t pass through to cool down and will stop working effectively.
  • Faulty thermostat. Coolant starts to flow through your car once the engine reaches a certain temperature. If your thermostat gets stuck when it’s closed, it won’t open to allow coolant to start flowing.
  • Poor airflow. If your cooling fan breaks down or the grate on the front of your car gets clogged with debris, this can stop air from circulating across the radiator, and your coolant won’t cool down as efficiently.
Driving an overheated car can cause damage to the engine, so it’s important to take care of the problem. Checking the coolant levels was the correct first step to take. If you can’t diagnose the problem from the list above, you’ll likely want to bring the car to a mechanic.
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