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Greetings - I am having an issue with my Honda Civic. Its a 2004 Civic LX with 173K miles. The car is bone stock and I am the original owner. Recently I noticed my ability to warm up the car slowly decreased. I took the necessary precautions; checked fluid level, replaced thermostat, purged system, etc and have had no change. The car has zero external leaks; I don't notice any coolant in the oil; I can't sense any coolant in the exhaust.

Here is where it gets goofy. If the car is running and warmed up, if I turn the heat on but the cabin fan off, the temp gauge reads normal (between H & C) but as soon as I turn the blower fan on (which works on all speeds), I begin to notice the temp gauge drop to "C". The air coming from the vents is warm but not hot (I don't think it would thaw snow off in the winter). If I change the temp from Hot to Cold, I can hear the internal diverter change and can feel the air go cold. The car has never overheated so I didn't think it would be a head gasket issue. I'm just stumped.

Any insight you could give would be greatly appreciated. Thanks for all of your time, I look forward to your responses.

 
Rep Power: 518

Seems like this would describe a bad thermostat, stuck open.
Heater is removing more heat than the engine has available.

Did you use a factory (Honda dealer) stat?

 
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(Face palm) I did not, I used a Napa "premium" thermostat. Have you found that the only T-stats that work well in these cars is the OEM? I have no objection buying OE parts but if I can get the same performance from aftermarket then I tend to be swayed that way. Maybe in this case, you get what you pay for, a waste of $15 on a junk T-stat, the cost of an OE unit and the joys of doing the job twice. thanks again for your insight though!

 
Rep Power: 518

It was a (somewhat educated) guess.

I've been in the trade long enough to be wary of (read: run like hell away from) a lot of aftermarket stuff......it's only gotten worse since most anything you could need is now outsourced to China.

If aftermarket parts have a 75% success rate, that's a 25% failure rate.
I don't want to make a living on 1 out of 4 jobs being a 'do-over for free'.




If you have a scanner, you could watch the actual coolant temp reading from the PCM as you drive and as you run the heater. (It would probably read about the same as what you can feel from the dash vents.)

 
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Ezone - thanks for your insight and advice. I think this weekend I'll try to hit the local Honda dealership and pick up a new thermostat and see if any change happens. Again I appreciate you taking the time out to answer my questions.

 
Rep Power: 308

I'm more then happy with Honda parts pricing.

I take online prices with me to dealer... and if the right parts guy is there he will come very close to matching them.