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Erratic overheating, intermittent warm HVAC air.


andyems

Question

This pertains to a '05 Civic but figured the process would be the same for any make and I've always had excellent help here. This will get long-winded but bear with me. I can do most anything when I know what part is bad and needs to be swapped. However, I'm horrible at trouble shooting and diagnosing.

Recently my wife tells me her Civic is not blowing warm air, even after the engine gets to the normal temp range. Several days later, before I had a day off to think about it, I noticed an antifreeze smell after driving it. I raised the hood and found the car had been blowing/boiling antifreeze out of the overflow reservoir. My dad said it acted to him as if the thermostat was bad. I replaced the t-stat and the overheating seemed to stop for the past 3 weeks. Wife said it still seems to be slow warming up but no overheating. Fast forward to today when we went for a drive in the mountains. All day of slow, curvy, up hill driving the car again performed fine, although we didn't use the heat since it was warm we had no cooling problems. After stopping to eat, the sun went down and the night cools off, leading to the need for warmth on the drive home. Again we have no inside heat. The temp gauge is in the normal range, but again it's just blowing cold air. After about 20 minutes of driving we notice the air finally begins to blow warm but the engine temperature gauge is climbing sky high. Car reads high for 45-60 seconds and the air from the vents cools back off. Suddenly the gauge drops to normal and the vent air gets warm again. I stop and check, and the car is blowing antifreeze out of the overflow again. The rest of the 45 minute drive home it constantly repeats the same process. The HVAC blows warm and temp gauge is normal for several minutes. The engine temp begins to climb and the air vents cool back off. It only reads high a few seconds and then the process repeats. I was thinking the t-stat is sticking even though it's new. Any ideas or advice would be awesome and very appreciative. I'll try and fix anything but I have no idea how to go about diagnosing this one. Thanks in advance.

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Ordered OEM timing belt kit off eBay from an actual Honda dealer. Parts finally came in yesterday. Took it to the mechanic this evening so he can start tomorrow. Since the episode almost two weeks ago this car has ran perfect. No a single issue of overheating, temp gauge has been perfect and it has blown warm air every day. It hasn't been this consistent in hearing issues in well over 6 weeks. No issues at all since my last episode. Guess I'll find out tomorrow evening. Thanks again for all the help.

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With all the typical summer festivities I forgot to post and update to my problem. Took it to a real mechanic and he was able to diagnose and fix the blown head gasket. He warmed up the car and stuck his camera into each cylinder. #2 fogged up his camera immediately. He told me that warm, moist air in there was a flag right off.

I also had been having intermittent upstream oxygen sensor issues over the past 2 years. It would throw a code and kick on the check engine light. I'd have it reset and it would run 3-4 months before lighting the indicator and the car as running fine. The sensor was the higher priced of the two on the car, around $250 for the part alone. Before I took it in it was starting to stay on constantly. I'd have it reset and the next day it would throw a code again. It was now totally dead. He replaced it, too, and didn't charge me any extra labor since my bill was already so high. $1150 later I have a new head gasket and oxygen sensor. Car is doing great.

Thanks to all for their help and advice.

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