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What causes a car to overheat?

What does it mean if a car starts to slowly heat up while idle but cools down when I accelerate?

Check if the radiator cooling fan(s) are turning on.



Thank you for your reply!
Is there anything else I should get checked? I’m just hoping it’s not pricey!!

What year, make and model are we dealing with?

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It’s a 2003 Honda Civic LX Sedan.

Most likely as previous poster said the electric cooling fans are never coming on . Could be as simple as a relay that controls those fans . Or it could be a water pump getting weak .


What’s pricey to one person is no big deal to another. $500 is my personal pain threshold.

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I’ll have to get it checked out. Is it okay to drive or is this something that should be looked into right away?

Right now $500 is a lot for me…

If the coolant level is low the engine could be damaged if you continue to drive.

The first thing I would check (when the engine is cold) is to see if the radiator is full of coolant. If not, top it off with pre-mixed coolant which is compatible with your car. I would also inspect the radiator cap itself–is the rubber seating surface hard as a rock, or even worse cracked?

The next thing I would check (also with the engine cold and not running) is to see if the cooling fan(s) turn easily by hand, or if the bearings seem tight or noisy. Most electric cooling fans have very little friction in the bearings, and if you give the fan blade a spin, it will turn freely.

Next, I would check to make sure that there are no damaged wiring harnesses, loose electrical connections, etc–for example, the coolant temperature sensor(s) and cooling fan(s).

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Absolutely. If it overheats, that could lead to major engine work.

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Thanks so much for your reply and for all the information. I plan to get it looked at tomorrow.

Factory radiator? That is alot of years on the radiator and if it has not been maintained properly it could have corrosion buildup inside it. Overheating at idle I agree with the other posts make sure your fans are coming on when you hit the operation temp, if the do then it could be the radiator.