I have problems with my 2004 Honda Civic. My engine overheats and there is no hot air coming to the cabin, even if the temperature gauge shows Hot. Every mechanic I know told me that it is a clear sign that the head gasket is blown (they never saw the car - they just guessed after hearing the symptoms from my description), so I started by removing the spark plugs and got an inspection camera inside the combustion chamber. I found some wet spots on the surface of the piston heads:

Piston 1 (Left)

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Piston 2 (Middle Left)

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Piston 3 (Middle Right)

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Piston 4 (Right)

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| Piston 1 | Piston 2 | Piston 3 | Piston 4 |

Do those wet spots indicate that there is coolant or oil leaking in? Piston 2 is bone dry, while the rest are slightly wet-ish.

I also looked at the spark plugs:

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But they look okay. It could be that it's been only one day since I noticed the overheating. The only thing that can be noticed on the spark plugs is that the one that goes on piston 2 (the dry piston) has some buildup on it and feels rustier. I'm planning to get a leak tester in the following days, but I was wondering if it is possible to actually detect a leak only by visual inspection. And why are three pistons wet and one dry?

  • Have you checked the coolant level?
    – HandyHowie
    Commented Sep 28, 2021 at 8:22
  • It is VERY common for the D17a engines in 2001-2005 Civics to have head gasket issues. This is usually due to people not using the blue Honda type coolant, but replacing it with "common" green coolant. With that said, though, when I pulled the head on my 2001 Civic a few years ago, there was a definite difference with piston #2, as it was clean while the rest looked like what yours do. Mine would overheat, but only if I didn't keep up with the coolant. As long as I replaced what was getting drank by the engine, it ran just fine. Commented Sep 28, 2021 at 9:38
  • I've had a head gasket leak a could of times and in both cases the #1 symptom was unexplained loss of coolant. I could sometimes smell coolant in the exhaust. But when I pulled the head there was one piston that was completely clean of carbon buildup. Clean like it was a new engine. I'm not seeing that here although I suspect that the leakage rate may impact the cleaning ability.
    – jwh20
    Commented Sep 28, 2021 at 10:04
  • A damaged head gasket usually results in lots of steam out the exhaust pipe as I suffered head gasket failures in a Ford 3.0 V6 twice. The second time coolant leaked into a cylinder, it created hydrolock, preventing the starter from cranking the engine. My coolant didn't show color changes while other vehicles may show a chocolate milk shake as combustion is forced into the cooling system. Did you check for a worn out leaking water pump? Rocking the pump pulley should not allow side play. Coolant stains are a clue to a worn pump.
    – F Dryer
    Commented Sep 28, 2021 at 16:37
  • It does look like something is odd with piston 2: it has more corrosion on the spark plugs and carbonization on the piston, but that's not enough to say for sure it's the head gasket. It could be it is and the leak is right at the piston 2, but it also could be some other thing like something with the fuel injector causing this carbonization. As HandyHowie asked, are you noticing the coolant level dropping?
    – IanC
    Commented Oct 28, 2021 at 23:30

1 Answer 1


Symptoms indicate coolant loss. If you are losing coolant, there are three places it can probably go: crankcase, tailpipe, driveway. If the coolant is going to your crankcase you must fix the leak - it's your head gasket - right away. You should see something that looks more like mud than oil on your dipstick. If it's dripping onto your driveway in significant amounts you should be able to see it. If it's going out your tailpipe, your only indication will be your radiator's makeup reservoir running dry. The tricky part of diagnosis (I speak from unhappy personal experience) is that the problem might only show up in a long trip or strenuous (hill climbing) driving.

BTW your use of a boresight camera is something that everyone should do, for everything. Just this week I used mine to get an image of my third floor gutters, recently cleaned, checking on the cleaning contractor. You could also use one to see how good a job you're doing flossing (not recommended, but they're so cheap you can buy extras, with one dedicated to oral hygiene).

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