97 honda civic is over heating but only on the highway

Maintenance/Repairs
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1

I have a 1997 honda civic and when I get on the highway at speeds of over 60 mph the temp on the car gets really hot at the top of the arc. Around town I drive with the air-conditioning on and the temp on the car stays at the bottom of the arc. All the time the outside air temperature is hot and humid, but it runs cool. I have checked the pressure of the radiator and the water pump works well. The fan also kicks on when its supposed to. I don’t know what else could be wrong. Pleas help

2

Have you replaced the thermostat? How about the radiator cap? Sometimes these two simple things get overlooked.

Pressure testing the radiator isn’t the same as pressure testing the cap.

I’m not sure what you mean by “the bottom of the arc,” but the needle of the temperature gauge should not be at the bottom. It should stay close to the middle all the time.

3

The problem might be with a partially restricted radiator.

When driving in town, the engine doesn’t produce as much heat as on the highway, and the water pump turns slower. So a partially restricted radiator will prevent the engine from overheating. But when driving at higher speeds, the engine produces more heat and the water pump turns faster. If the radiator is restricted to the point where not enough coolant can pass through the radiator to remove the engine heat under this condition, the engine starts to overheat.

Tester

4

If I understand the post correctly it’s getting too hot on the highway and staying cold around town?

Assuming (since you say you’ve checked the “pressure of the radiator”) that you’ve checked the fluid level, I’m going to suggest a thermostat stuck partially open.

The T-stat should be allowing sufficient flow of coolant on the highway AND allowing the engine to warm up around town by controlling the flow.

5

While I agree with the answers above, and they are likely correct, I will add that it is also possible the water pump (Would we not call them coolant pumps?) could also be the problem.

6

Thank you all for your help. I’ve changed all the things that everyone discussed and now it doesn’t overheat.