Hello everyone! I'm brand new to this forum but a long time follower. I'm very impressed with the expertise of the active members and thought I'd throw out another overheating situation to join all the others. I've read through many of the older posts and have a lot of ideas to try and fix my problem but perhaps I missed something or there are other ideas to try.

Background:
I have a 2005 Civic EX that was overheating a few months ago. Unfortunately, after a new thermostat was installed thinking this was the root of the problem since there were no other symptoms (other than the temp gauge reading hot!), the car was ran hot for a month or two. Car seized up since it melted a lot of vital components and now there's a new radiator, recently machined head gaskets, new thermostat, new water pump, and new timing belt. Last week, the car began running hot again. Took it to a different shop who did a pressure test and found a manufacture defect in the new radiator (pin hole size leak) and replaced it. Yesterday, it ran hot again. I checked the coolant levels and the level in the reserve was fine and only had to add a little bit in the radiator itself. Took it for a short test drive and the temp gauge was normal (just below half way point). Today, it ran hot again but came down a bit when the A/C was turned on.

Forward plan:
Any suggestions? After reading the many threads on this topic (what is it with Civics and overheating??), I plan on burping the system, checking that both fans turn on when the A/C is on, and replace the coolant fan switch (that's near the themostat housing) and the ECT sensor (that's in the thermostat housing) just to do it since I'm sick of dealing with this situation! Any other thoughts or suggestions? Any help would be appreciated! I am a noob so I'll apologize upfront for the stupid follow-up questions I'm sure to have like where something is and whatnot...

 

I'd definitely check for the fan operation. When you turned on the a/c, the engine cooled down, which would indicate to me that the fan turned on with the a/c, which should be normal. This in turn would indicate that the normal cooling fan isn't turning on when it should.

I'm not sure what voltage range should be (I'll bet mk378 does), but I'd check to make sure there's current going to the fan. If there is, the fan motor could be bad. If there's not, it's probably one of the sensors you mentioned.

Any check engine lights?

 

Thanks ChristianL for the response! I just checked the fans and they do indeed work (both of them) and there is not any check engine lights on. I just changed out the switch and sensor, topped off the radiator with more fluid and about to take a test drive. Is there anything else I can do to test or just wait until it overheats again?

 

During our test run, the car ran fine. We went through a subdivision, drove on a freeway, everything looked good. Unfortunately, about 3 blocks from the house, I decided to turn on the A/C and immediately, the temperature gauge went off the scale high. I drove around a bit to play with the A/C to see if it were correlated and it's hard to say. I turned it off, the gauge went down to about 3/4. Turned on the A/C to low, gauge stayed the same. Turned it on high, stayed the same, maybe even went down a bit. It never went off scale high again. Went I got home, I looked over a few more threads and forums and saw how to check whether you have a bad thermostat or not. I tried it even though it's only a few months old and it seemed to me the upper radiator hose was hot but the lower one was just warm. There definitely was a difference in temperature. So, I decided to replace the thermostat too. It was an interesting experience, especially trying to seat it when putting the housing back onto it but I managed. I took it for another spin, turn the A/C on/off and the gauge stayed in the normal position. In the past, it seemed random when it would go off scale high so I think the true test will be a day of normal driving tomorrow...more to come!

 

Fan switch? Put key to on position but you can leave engine off. Fan switch is on thermostat housing, should be getting 5v relative to ground, short it with a paper clip or whatever and see if the fan pops on. It should (if not check wiring). Then run the car and start burping it (youll have to look it up for your year and model, but it tends to take a long time you gotta be patient and do that right, it is VERY important), watch the gauge and the radiator fan and make sure the fan is coming and that the engine does not get hot. If it gets hot it could be bad thermostat/fan switch. If you bleed the cooling system of all air and it still overheats then consider a bad water pump or clogged radiator/hose? If air never stops coming from radiator you probably have a hose leaking air in, replace that; this can possibly be a potential sign of bad head gasket though.

ps. technically you are supposed to put a sealant around the thermostat housing when you put it back on!

 

So, here's another piece to the puzzle. My check engine light just came on! When starting the engine, it starts/idles rough and the light comes on, however, the temperature is normal. What the @#$!??? I'll be going to the auto parts store to see what the code is after work so stay tuned for more to this ridiculous saga...

 

Thanks for the good info! I didn't know about the sealant but I was wondering about it as when I pulled the old one off, there was a little bit of gunk around the rubber ring but I didn't think there was enough to have been intentionally put on there. I replaced the fan switch and ECT sensor and now, thermostat. I thought I bled the system of all air but I'll double check the manual and make sure I followed it. Now that the check engine light came on, I'm praying I've moved passed the cooling system problems...

 

The car never made it to an auto parts store to check the code. While on the feeder of a freeway, white smoke started coming out from underneath the hood and the check engine light went from steadily on to flashing. I let it cool down, added a lot more coolant and drove it to my mechanic. Oddly enough, it ran fine when I drove it to the shop though the check engine light was on (not flashing, just on).

 

Oh man that does not sound good -_-

I hope a hose just busted (thats what happened to me) an it is not your head. Keep us updated!

 

Well it's been an interested week so far. After the latest saga above, here's the latest: took the car to my mechanic after it overheated and started smoking. It was ok to drive as I added a ton of coolant and it never overheated or smoked while driving the few miles to the mechanic. He checked the code and it was a cylinder 3 misfire. He checked the ignition coil and it was bad (the cause of the smoking). Replaced it and it was all good. That took care of the smoking issues and as a side note, when the car originally overheated last year and got so hot to melt things, he had told us these coils would eventually go out and that we should replace them but we didn't at the time to save some cash as that time we had to machine the head. I went ahead and replaced 2 other coils as the #1 was still good but the others were in bad shape. Afterwards he then pressure checked everything again and nothing. Everything checked out fine, no leaks in the radiator or hoses, no bad head, etc. He bled the system of any air and it ran fine for him. So, we pick up the car on Monday. On Tuesday, it overheats again! WTF??? I called my mechanic and he said the only thing that we could try is replacing the thermostat again but with a Honda part and not an after market one. He's thinking that maybe this could be the cause as everything else has checked out fine. Thoughts?? It's a cheap thing to try and will be replacing it later today...more to come unfortunately...