OK, I just came out of the garage after doing a leak down test on this 2.5 DOHC in my '97 OBW and I have got some funky results. I've seen bubbles in the coolant before with the engine running and up to operating temp. The compression test looked good (172-180) on all but #3, which had all of 28psi. I put the crank damper timing mark on zero, dead-nuts-on TDC for #3 and I got an 50% reading on the leak down. No surprise there, given the compression test result. I ran around the car and found air moving fast out the tail pipe AND the #1 spark plug hole, but don't feel anything worth mentioning on the intake, dipstick tube, or the opposite bank of spark plug holes.

 

Sounds like a blown head gasket right between the 1 & 3 cylinder, right? Here's where you earn your beer for the night: when I swap the leak down test to the #1 cylinder after rotating the crank 360*, I get 8% loss and can hear just a wee bit of air moving through the intake and exhaust. I'm guessing the #1 valves aren't sealing up perfectly. But if the head gasket is shot so badly that it allows enough air to leave the #3 cylinder that it empties my 30 gallon compressor tank in 75 seconds, how in the #$^*#$@#@ can the #1 cylinder be sealed up as tight as a ducks rump roast?

 

Anyone?

 

 

Anyone?

 

 

Bueller?

Well, the only thing I can think of (and this is strictly theory) is that the HG tore at one edge and is swinging like a door. The material "swings" open with compression from cyl. 3, but "swings" closed with compression from cyl. 1. Just an idea........

I see what you're saying. It makes perfect sense. But when I tried to blow that theory out of the water by running my compressor up to the max, it didn't make a damned bit of difference. Go figure.

 

How the hell am I supposed to sleep tonight with this great mystery sitting out in my garage? Hmmm, might have to call in sick tomorrow!

Maybe the exhaust valve is open on #1 when you are doing the leak down test on #3 ??? So the air bypassing the #3 exhaust valve ( probably burnt) is going down the exhaust pipe and back into the #1 cylinder through the open exhaust valve

 

Sea#3

"how in the #$^*#$@#@ can the #1 cylinder be sealed up as tight as a ducks rump roast?"

 

Duck tape?

Riiiiiight, duck tape. I hadn't thought of that. You're pretty good.