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2005 Civic overheating because of head gasket

My 2005 Civic is overheating at random times. My mechanic couldn’t find the problem so I took it to the dealer and they replaced the thermostat and a fan switch. That didn’t work so now they tell me I have a blown head gasket ($1,458)… but there’s no water in the oil and no gray smoke. They say the coolant leaks into the block until there’s not enough circulating and it overheats. Then, when it cools, the coolant goes back into the reservoir and that’s why it never seems to be low on coolant. WHAT THE…!!! Has anybody ever heard of something like this? I’ve seen other Civic overheating letters (including a 2005 that sounded like my exact problem) but I never saw an update about what fixed the problem.

They are out of ideas and trying to fleece you with guesses. Can you tell us what the conditions are when the overheating occurs? Is it cruising on the highway, or stuck in slow moving traffic? Hot day, cool day? A/C on or off? Frequency of events?

Just for the record, a random overheating that doesn’t seem connected to certain driving conditions usually means random air pockets or a cooling system partially clogged. Have you had the coolant changed out?

How many miles on car? 8yrs old. Let’s say 100k? New timing belt/waterpump? Coolant has been flushed/changed?

Have you changed the radiator cap? It might not be holding pressure.
Had similar symptom on one of my Accords way back when.

Offhand, sounds like they’re throwing the head gasket thing out there as an expensive, misguided guess and changing the radiator cap might be a good idea.
Make sure the radiator is topped off with a new cap and don’t rely on what’s in the overflow bottle.

It could be a head gasket.

I’ve seen head gaskets develope a leak at one of the fire rings. The hot combustion gasses then find a path to a water jacket the head gasket is suppose to keep sealed. These combustion gasses then superheat the coolant and the engine overheats. The flawed section in the leaking head gasket can act as a check valve. That is, the combustion gasses are allowed to the water jacket, but when the engine is turned off the pressure of the cooling system pushes on the flawed section of the head gasket, causing it close and coolant isn’t allowed back into the combustion chamber.

A head gasket leak won’t always result with coolant in the oil or steam out the exhaust pipe.


problem started a few months ago with random overheating at stoplights (maybe once every 10 days. Replaced thermostat and fan sensor but it overheated again so I took it to the Honda dealer. Replaced the thermostat and another fan switch (said the thermostat I put in wasn’t an official Honda part so it probably wasn’t working right. It overheated slightly a week later and once more a few days after that. I had to drive about 2 hours on the freeway last weekend and about an hour into it the gauge started going up (level ground and just cruising at 70)- this was the first incident on the freeway that i’d had. It creeped up a couple more times and went back down. Once it got halfway between normal and the red mark and was still moving slowly up so i pulled to the side but by the time I moved over it started back down. There were 2 major uphill grades after that and it sat right on normal temp on both of them when the engine was working harder.
Shop today looked it over and said probably the radiator… but you can’t test it, just replace it. I’ll try the radiator cap- I don’t think it was replaced yet. Car has 133,000

Thanks for the help everyone!

'Shop today looked it over and said probably the radiator... but you can't test it, just replace it.'

You can, indeed, flow test a radiator. I think this shop simply doesn’t have the equipment. Is this the same shop that suggested the head gasket?

No. They thought the head gasket idea sounded far fetched. I’m getting a new radiator cap tomorrow- if this is going to be a “keep replacing until something works” repair I may as well start with the cap and then I’ll get the radiator checked.

Once coolant “lears into the block” it doesn’t return. Avoid ever going to whoever told you that.

I recently had to replace the head gasket on my fiancees 2001 civic. The main symptoms were that it overheated in city driving and when getting off the highway, there was a misfire CEL code, and the car would sometimes drive like crap (no power, lots of hesitation, sometimes even stalling). The coolant reservoir was always full, but if you took off the radiator cap, you would see the radiator was low-- so there was coolant going somewhere. I had the car pressure tested and it came back OK, and replaced the thermostat and radiator cap with no luck. I (correctly) guessed it was the head gasket when I filled up the radiator and let the car idle with the cap off while parked on an upward incline. I watched for about 30-45 minutes, keeping the radiator topped off, and saw bubbles coming up, as if the I was bleeding the system with new air pockets bleeding out for the whole time (when the bubbles popped, it looked either like smoke or steam was coming out of them). I also noticed that the coolant in the reservoir would be bubbling after driving the car a little hard/getting off the highway (it actually overflowed the reservoir once). Also, after i got all the parts and tools together for the job, i noticed bit of brown precipitate under the radiator cap. When i drained the coolant and let it settle in the waste container, there was a ton of this brown stuff easily seen. AfterI got the head off, there was a clear line of this brown precipitate running down the edge of the water jacket, going with the check valve idea tester was talking about.

So before you go spending the money on a head gasket, it might be a good idea to look for bubbles in the reservoir after driving on the highway and make sure that the radiator itself is full of coolant. Youtube has a lot of really great videos of the bubbling I am talking about. I also understand there is a test where you see if there is combustion gas in the radiator. I believe the dealer will do this for you, or you can buy the kit and do it yourself for about the same amount of money. You could also take it to a shop and ask to do a cylinder pressure test with about 100 PSI while watching for bubbles coming out of the radiator.

FYI if you do end up getting a new head gasket and you haven’t replaced your timing belt, tensioner, and water pump, i would imagine the shop would throw those on for cheap while doing the labor (I had unfortunately just replaced them a month before the head gasket went)

It’s true that a head gasket can be bad with no or very little loss of coolant. Their explanation? Not so much. There’s a variety of tests to confirm/disprove the head gasket hypothesis. There’s no need for any ambiguities on that issue. A good shop would test the things mentioned above, bubbles in coolant, a chemical test for hydrocarbons (exhaust gas) in the coolant, a cylinder leak down test, a cooling system pressure test, compression test, etc. Sometimes the best thing to do is take the car to the local radiator shop. Those guys deal with cooling system problems every day and have the test equipment and expertise and are often able to offer up good practical suggestions that have worked before.