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Can pressure tests push water into the cylinder? How much pressure loss is acceptable in a cooling system test?


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TheGrinder(ofgears)
User

Aug 16, 2021, 8:54 PM

Post #1 of 3 (512 views)
Can pressure tests push water into the cylinder? How much pressure loss is acceptable in a cooling system test? Sign In

I was worried about doing a cooling system pressure test with cars of unknown headgasket condition because I wouldn't want to push water into the cylinder and then cause a hydrolock, bent rod, steam detonation, etc. but it occurred to me that cooling systems stay pressurized for a good, idk, say half hour after you turn the car off? when they would be creating the same ingress, if any, as a pressure test. does this theory hold water, so to speak? or is there a greater risk doing the test than just driving the car?

used the astro pneumatic 78585 cooling system pressure tester for the first time tonight.

the instructions say if you lose "a significant amount" of pressure, then you have a leak. how much is "significant"?

one car showed between 1 and 1.5 psi pressure loss over a half hour and the other lost about half a psi over 30-40 minutes. do these things typically lose some pressure on their first couple uses because of parts stretching and what not? I used a well worn loaner from autozone a couple years ago (on a different, third car) that showed no noticeable loss in pressure.

no leaks visible in the engine compartments (even with uv dye in the 2nd car). let's say it's not from breaking in the tester. are these kinds of pressure drops indicative of a headgastket leak?


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 16, 2021, 10:05 PM

Post #2 of 3 (500 views)
Re: Can pressure tests push water into the cylinder? How much pressure loss is acceptable in a cooling system test? Sign In

YES. From just subject line you didn't need to say more. It could hydro-lock if starter is strong enough do damage. Do that AYOR or take plugs out and turn engine by crank bolt first if worried.
Coolant in one or more cylinders shows as wet spark plugs or very clean if it can burn the coolant off vs the others about ends the hunt for the problem.
> The reason would usually be a head gasket but assorted liquid cooled engines can use coolant in intake manifolds also the source leak(s) you hunt down till you are convinced then choose the fix can still be obscure till parts are removed if cracked items or gaskets,


T



Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 17, 2021, 4:27 AM

Post #3 of 3 (475 views)
Re: Can pressure tests push water into the cylinder? How much pressure loss is acceptable in a cooling system test? Sign In

If your pressure test happens to push enough coolant into the cylinder to hydro lock the engine, then you have simply proven the engine is shot. Any engine that leaks that much coolant is DOA anyway.

Hydro locking is the least of your worries if that happens.

If there is any question at all of a blown head gasket, just remove the spark plugs and leave the pressure on it for hours to see if anything gets into the cylinder.



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