Compression loss after overheating?


New Member
Hello all,

I am new to and have really enjoyed all of the albums, knowledge and discussions that I have read thus far.

I am posting this thread because I am in a pickle. To start, I have what I would call, little knowledge on imports and the inner-goings on of motors. I have some knowledge, but not enough to fix my problem.

I have a 94 RS with a 1.8L B18B1. I was driving home one cold evening and the temp went up. Knowing that you should never drive a hot vehicle and the inability to get a tow truck at the late hour, I waited until it cooled and finished my journey home (about 10 minutes of driving after an hour or so letting it cool). the next day I ensured that it was full of coolant/water and I checked for leaks. I also changed the thermo. I drove it to work and again, it overheated. Same story, I waited for it to cool and tried to drive it home, but it wouldn't start. I called a tow truck and had it delivered to my house.

I found that the water pump had broken into 3 pieces and the breaking of the water pump snapped my timing belt (I imagine that the pump seized and when it did, it snapped the timing belt). Threw another water pump and belt on it, and after figuring out some timing issues, it fired right up.

The issue is that water was not circulating at all. I let it run until it got warm and checked everywhere I could think of to see if water was circulating. The reason that I know it was not circulating is because after reaching normal operating temperature, and the fans kicked on, I was able to take the hose from the other side of the thermo OFF and nothing came out, at all. It then developed a miss (im thinking head gasket). I shut it off to let it cool down, in fact I let it sit over night. The next day I needed to pull it from the driveway into the garage but it wouldn't start (I live on a crazy hill so I couldn't just push it). One of my hot rod friends looked at it briefly and said that I have NO compression in any of my cylinders. He didn't use a compression tool, he put cap to a pepsi bottle on it and as I cranked it, he said he felt no compression (obviously this lets you know that we are a couple professionals, lol).

My first thought is that I cracked the block, because of the hot temps and the it being aluminum, but I am being told that it could be just a blown head gasket (no oil in water/water in oil and I don't see any leaks - but it does explain the pre-non starting miss development), I am also being told that it could be a warped head or that the cylinders could have swelled from the hot temp and are not tight for the pistons (I think you all call this cooking the rings). Anyway...

Any idea of what this could be? How can I figure out what it most likely is without a shop? Any and all help is Greatly appreciated.


Not a M0derator
Welcome to the site and very well written post.

lol @ your compression diagnosis without a compression tool.

You don't have a cracked block or cooked piston rings. That's highly improbably from overheating.

You either have warped the head/deck surface enough to break the head gasket seal OR you bent valves when the timing belt broke. Get a proper compression tool and perform the test. Im leaning towards bent valves which would result in zero or extremely low compression in that cylinder. This would explain your hard start.

To replace the valves you have to remove the head in which case you would have to replace the head gasket as well. Two birds, one headache?


New Member
After the timing belt broke, the car would still start. At least it did a few times. Could bent valves still be a cause? Where would you recommend me getting a compression tool from.

(this is all new to me, so I may ask some pretty simplistic questions)

No matter which cause (warped head or bent valves), machining the head is necessary? Correct?

Two birds, one migraine. You hit that nail on the head.


Not a M0derator
Its either bent valves or the tbelt isnt properly aligned and the mechanical timing is off between cams and crank. You can visually inspect that #1 lines up with crank at TDC.

Machining the head may not be necessary and often its not. I really don't think that's the cause of you problem and it sounds like you did a good job at make sure the engine didn't over heat too severely. You can check the flatness of the head/deck surface with a straight edge or you can bring the head to a machine shop and ask them to check it for you.

A compression tester can be bought at any auto store for $20 bucks.