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I have an automatic 2004 Honda Civic coupe. Its been overheating. I bought it in December 2015. Within 90 days, it was running hot. I took it to a shop and they said there was an air bubble in the system. They got the air bubble out of the car, and it ran smooth. Fast forward to July 2017. The car starts running hot after running 300+ miles on highways. I limp it 30 miles to a shop (mostly highway miles) and the shop says its the fans. Those get replaced. Car runs OK. Approx 240 highway miles later, the car starts over heating again. I turn the heat on full blast, and drive on the highway from Knoxville, TN to Atlanta, GA. I go to a shop. They says its the thermostat. It is replaced. The car runs fine. Fast forward to two weeks ago. The car starts running hot again. I take it to a shop. They bleed out a bubble they found, and replace the water pump just to be safe. At no time during this mess did the car act up, no steam, no performance issues, etc. I asked the shop if they found coolant in the oil, or vice versa. They said no. I took the car for a little mountain driving tonight and about 1/3 of the way up the mountain the car starts running hot. I turn the heat on and turn around. The fans aren't blowing hot for the internal vents in the car. The moment I pushed the defrost button, heat started coming out. After 90 seconds, the car was a normally operating temp. I limped it home to Franklin, NC to Atlanta, GA. This pattern happened a lot. Once I got the car on the highway, it would cool off to normal within 2 minutes every time. I don't think its a head gasket, because the fluids aren't mixing and I have no performance issues. The coolant levels are fine.

Does anyone know what the problem could be? Note: I've seen similar posts but none with the car cooling so quickly and I've ruled out most major components.

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I had almost the same exact issue with my Honda Civic. Went to a shop countless times - radiator replaced, hoses replaced, fans checked, thermostat, waterpump etc. Eventually I let a guy tool around with it for a few weeks and it turned out to be a very small leak in the head gasket that would only cause issues after more than an hour of driving.

My advice to you would be to get your head gasket thoroughly tested for leaks. Once I got mine replaced, I had no issues again on several long trips.

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Well I heavily think that the fans themselves are in question even though you said they were replaced. There are fan timer units and Control modules that control the actual operation and kick on of the fans themselves that could be malfunctioning. Rad clog seems unlikely since the car cools down on highway speeds now (makes sense because more speed = more air coming through the rad). Check your coolant temp sensor that relays info to something like a timer control module and check that module also. (refer to your cars online manual if you don’t have a hard copy). If you don’t want to check ohms etc then just replace the sensor. If the timer module is seeming to be malfunctioning (meaning the temp sensor is good), then you should open up that module and check for cracked solder joints and repair them if you can’t find a new or junkyard part to replace it.

  • The components you mentioned being faulty shouldn't introduce air bubbles right? Also, why would things work for awhile after going to a shop? – Dan Gifford Apr 1 '18 at 2:16
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    No, air bubbles can’t be introduced by these temp sensors/timer units because they control the electric fan system, not directly the cooling system, after going to the shop it works for awhile most likely because the coolant is heating up as you go, and depending on how fast you drive after your shop visit can determine how fast you overheat (more speed=more cooling after all) so there’s a lot of factors coming into play. How fast were you driving on the mountains? At highway speeds you sometimes don’t even need rad fans as the air coming at it can be sufficient to cool it (in certain cases) – sjfklsdafjks Apr 1 '18 at 12:38

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