q240z Posted August 4, 2005 Share Posted August 4, 2005 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? Quote Link to comment Share on other sites More sharing options...
Dr.Outback Posted August 4, 2005 Share Posted August 4, 2005 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........ Quote Link to comment Share on other sites More sharing options...
q240z Posted August 4, 2005 Author Share Posted August 4, 2005 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! Quote Link to comment Share on other sites More sharing options...
sea#3 Posted August 4, 2005 Share Posted August 4, 2005 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 Quote Link to comment Share on other sites More sharing options...
brus brother Posted August 4, 2005 Share Posted August 4, 2005 "how in the #$^*#$@#@ can the #1 cylinder be sealed up as tight as a ducks rump roast?" Duck tape? Quote Link to comment Share on other sites More sharing options...
q240z Posted August 4, 2005 Author Share Posted August 4, 2005 Riiiiiight, duck tape. I hadn't thought of that. You're pretty good. Quote Link to comment Share on other sites More sharing options...
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