One of my cylinders is leaking and I have determined so far that at least one or both of the intake valves are leaking. However, now that I have that cylinder head off, I would also like to test the piston ring. Can I pour water in the combustion cavity when the cylinder is in bottom dead center and see if it loses water, catching it under the lower oil pan where I normally drain oil on change? I can such the leftover water (hopefully all of it) out of the combustion chamber using a syringe.


1 Answer 1


Basically, no. You're going to lose fluid past the rings no matter what, plus, how are you going to measure this anyways? This isn't how you test your piston rings.

The way to test your piston rings is two fold. First, you can check for blow-by. This isn't a quantitative test (or there's no real way to quantify blow-by). You can look to see, while the engine is running to see how much blow by is making it up through the crankcase. If you see it increasing, you know there's an issue with your piston rings not controlling the combustion gasses.

Secondarily, you can do a compression test. This is a quantitative test. Every production engine will have a specification for compression. As long as you do the test correctly, you're going to be able to check compression two ways. First, check it against what the standard is. Secondly, you check each cylinder against the others. There should be very little variance between cylinders (ie: all should be within say 10% of each other).

Both of these things can only be done with a complete put-together engine. You don't check your rings with the heads off.

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    Or do a Morse test.
    – Solar Mike
    Dec 25, 2021 at 23:30
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    They can be hired. And can give a different result cf a compression test.
    – Solar Mike
    Dec 25, 2021 at 23:36
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    @SolarMike - Correct, if you can find one. A compression gauge costs $40-50 and can be picked up from the local parts store or ordered online. Then, to use it, you can keep it in your back pocket. To do a Morse test, you have to first find a dyno, then figure out when they can fit you in, then pay the fees to do the test, which can easily run a couple hundred dollars if they'll let you run your own test ... more if they don't. The compression test will more than tell you what you need to know without all the hassle or expense. Dec 25, 2021 at 23:42
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    Spent several hundred hours running engines on dynos including a jet engine. So I know exactly the info that can be obtained - and you won’t get it from a compression gauge.
    – Solar Mike
    Dec 25, 2021 at 23:48
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    You can't do it with the head off. @SolarMike - Yes, I'm sure you have, which also means you know using a compression gauge is an indicator of the function of the engine. Not everyone can own or use a dyno at their whim. Even most professional mechanics don't have easy access to a dyno and even if they did, most wouldn't use it because it takes too much time to obtain results which aren't that much better than a compression test. Seriously, I don't understand why you are arguing such a point as this, because you have to know what I'm saying is correct. Dec 25, 2021 at 23:59

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