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I've always been able to find answers to my questions/problems by searching the forum but I can't figure this one out. Hopefully, one of you can help.

Problem is that I get coolant/bubbles pushing into the overflow tank. The weird thing is that it only does it in the summer (i.e. - it's hot enough to run the AC). I was fighting this last summer, the weather cooled down and it stopped. If I run it at highway speed for about an hour, about a cup of coolant will blow into the overflow tank. I just wait for it to cool down and dump it back into the radiator.

Before everyone starts telling me it's the head gasket, both myself and a mechanic did the block leak test and it passed (no exhaust in the coolant)! There's no oil in the coolant, no coolant in the oil, no white smoke. It runs fine. The car has never been overheated. It does have alot of miles on it (184,000).

I've changed the radiator cap and the thermostat - no help. I've performed the coolant air bleed procedure several times - no help (it doesn't stop bubbling after running for 30 minutes with the radiator cap off).

The #1 spark plug looks a little different than the other three. There's some rust/corrosion on the end of the threads. The electrode looks normal. I would do a leak down test on it, but none of the auto parts stores around here lend the tester.

Any ideas?

 
Rep Power: 812

bubbles that never go away with bleeding is usually the start of a bad headgasket (small leak) which convertional tests will not show til it gets worse. if it is leaking coolant into the cylinder, you will never have any mixing of oil and coolant. it will just burn off or force bubbles into the coolant. only other thing is a faulty thermostat if you used aftermarket instead of honda. same for the radiator cap. the aftermarkets are junk.

 
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The radiator cap and thermostat I installed were after market (Duralast). I'll try ones from Honda.

 
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Well, I switched to a new Honda radiator cap and thermostat. Still bubbling away. I took the plugs out again. The #1 plug looks slighly different than the other three. It's hard to tell from the pictures, but there's more oily residue on the end of the threads than the other three. Overall, I'd say they look pretty good.

 
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I just had this happen to me. it would do this every now and again for a couple weeks. Your head gasket is starting to go bad. Once myn misfired on 3 cylinders and it was water in it. about a week later there was no circulation. bad head gasket but if your a mechanic, get on rockauto . com and they have rediculously low prices on everything. i got my headgasket set for like 50 bucks shipped

 
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Yeah, I think you're right - the head gasket is starting to go. The weird thing is that it's been doing this for over a year. I was fighting with this problem last summer (blowing coolant into the overflow tank). It stopped when the weather cooled down. Same thing this summer.

I'm starting to look at new cars. Hopefully I can get this one past the dealer trade-in inspection without them realizing the head gasket is about to blow.

 
Rep Power: 812

yeah usually they dont care much. they will do a quick check of it to determine overall quality and get you out with a new car. the mechanics can play with it later and fix the broken stuff.

 
Rep Power: 313

This could go like this for years without getting any worse.. Hell, it could go the life of the car. Keep driving it just check your coolant every once in a while.

 
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I've considered that (continuing to drive it). Problem is that I won't drive it if the trip is more than an hour or so. If I go too far, it will start overflowing the recovery tank. I can manage that most of the time by taking our other vehicle, but that's a gas-guzzling Chevy Trailblazer. Plus, my wife says she's afraid to drive the Civic - combination of the miles, age, and the fact that I do the work on it!!!

I like to drive cars a long time, but at some point you have to look at the safety aspects of driving an old car. I don't fear that the car is going to "fall apart" as I'm driving it, but it lacks so many of the features that are available today. My Civic has two air bags, but doesn't even have daytime running lights - much less electronic stability control, anti-lock brakes, or side curtain air bags.

 
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I almost hate to ask this, but has anyone had any suceess with the head gasket sealer products? I know I should fix the problem, not cover it up - but it seems like my car would be a good candidate for a sealer because it's just a minor leak right now.

Anyone try one that works?

P.S. I didn't put this in any of the other posts, but I did try over torquing the head bolts a couple months ago (per an old Gearbox post). Factory spec is 49 ft/lbs. I went up to 65 ft/lbs in three steps following the order in the service manual.

 
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the leak sealers will make a mess of your whole cooling system and possibly ruin the motor. i wouldnt risk it. overtorque the bolts is the best bandaid option until you can fix it.

 
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I second that vote for NOT using sealants. I had an 85 Seville which was the WORST with gasket failure, and the forums for that engine were chalk full of warnings. DONT USE THE CRAP. It will nee fixing in the end, if you seal it and it works(rare thing from my experience) youll just need to fix it anyways. If it works shortly or just doesnt, you wasted 30-100 bucks depending, and now need to fix it or the engine is capoot. Tighten the bolts, ride easy then fix it.