AngeloM

I'm having a strange issue with my new (to me) 2004 Civic. I bought it a few weeks ago, and around town, along with short city expressway trips, the coolant temperature is rock solid. Yesterday, I hit the road to go from Chicago to Montana. About 50 miles out, the temperature started to go up when I got off for gas, but went back down again as I got back on the highway. Went another 200 miles, again, the temp stayed right where it should. Until I got off to get some gas. After the first stop sign, the temp went right to the red, even while moving. I stopped the car, let it cool and asked around about a mechanic. When I found a shop address, the car was fine as I drove there.

The car was a little low on coolant, which he refilled. Sitting there, idling, it would not overheat. The fans came on, no problem there. But I definitely am pushing coolant after highway driving, the reservoir was overflowing. I turned around and started heading back home, the temp was fine until a toll stop about 100miles down the road, then it went to redline again, I pulled off, put in some more coolant, then it was fine the rest of the way.

The mechanic thought it might be a head gasket, saying something was pressuring the coolant out of the radiator. I tried one of those exhaust gas test kits, but I keep getting coolant into the tester, ruining the results. Both hoses feel warm, so it doesn't seem to be the thermostat. Besides, I was running for hours at 70 with the AC on - maybe it's a very small head gasket leak, that takes time and the stress of highway driving to make it leak?

I've seen others with overheating issues, but this seems unique, where it only happens on long trips.

thanks for your help.

prodjay10

If you've gone thru diagnosing and it still overheats, it'll be a head gasket. Like you said, the compression gasses won't go into coolant unless at highway speed. When testing, it's idling.

First Check for:
Coolant level.
Thermostat.
​Radiator Cap.
Leaks by pressurizing radiator.
Maybe caused by restriction in radiator or heater core.
Damaged water pump. Sometimes they are so corroded that the blades fall off.
Head gasket.

Mine was like yours and just kept getting worse. A cracked radiator allowed it to overheat then it became a head gasket.

I forgot to add

Make sure the radiator fan and condenser fan kick on when they are supposed to.

You have to hold the tester right above the filler neck on the radiator. As close to it without touching. Otherwise you'll suck up the coolant.