Cracked Cylinder Diagnosis: Pressurize the Cylinder

Video Transcript

DOUG JENKINS: Hi. I'm Doug. I work with 20 great guys in St. Louis at Doug Jenkins Custom Hot Rods, and we're going to do some work for you today on Expert Village. The next thing we're going to do is we're going to pressurize the cylinder we suspect has the problem. This hose goes with a leak-down kit. Dan is going to insert it in cylinder 6 right now. That's the one that we suspect has the problem. And so he screws that hose in there and it allows him to hook up the hose from the air compressor. It runs between 90 and 110 pounds of pressure, and he's going to inflate that cylinder. And we'll see if we can see bubbles coming up in the radiator at that point, and that would be a sure indicator that there's a problem with that cylinder. If the bubbles don't come right away, we'll turn the motor a little bit, make sure that we get it at any point in its reach. If there is a crack in the cylinder wall, it'll show up that way. Now Dan is hooking up the hose directly from the air compressor. It's a lot of pressure, and he's hooking it up to cylinder number 6, trying to inflate that and watching for bubbles in the radiator. Whoa, whoa. Okay, we found our leak. So what we got here is pressure on cylinder number 6, air pressure in the cylinder with an air hose. Your combustion chamber and your coolant system are supposed to be separate, so he wasn't able to get good pressure there, so he bumps the key over a little bit until both the intake and exhaust valve closes. As soon as he had pressure, water comes gushing out of there, indicating probably a severe crack in the cylinder wall or--I've never seen a head gasket leak that bad, but it could be.

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