Bad Leakdown number
Thread Starter
Drifting
Joined: Aug 2002
Posts: 2,557
Likes: 14
From: Dallas, TX
Bad Leakdown number
How important are leakdown numbers on a 3.6? The car I've looked at has been well maintained, but the leakdown showed 15% loss with one cylinder 22% loss. The compressions numbers were great at ~175.
I am somewhat confused. How can the compression showed good, but the leakdown indicated something else?
Is Bruce Anderson right? That leakdown is not a valid test of the engine's condition? The PPI mechanics from a well respected shop said he trusted leakdown numbers more.
BTW, on the cylinder /w 22% leakdown, the air loss seemed to come from the intake side.
thanks,
anthony
I am somewhat confused. How can the compression showed good, but the leakdown indicated something else?
Is Bruce Anderson right? That leakdown is not a valid test of the engine's condition? The PPI mechanics from a well respected shop said he trusted leakdown numbers more.
BTW, on the cylinder /w 22% leakdown, the air loss seemed to come from the intake side.
thanks,
anthony
Drifting
Joined: Nov 2001
Posts: 2,689
Likes: 5
From: Leeds, where I have run into this many lamp
Anthony
have a read here
<a href="http://www.pumaracing.co.uk/comp.htm" target="_blank">Leak down tests</a>
His other pages a pretty informative too, especially because he isn't really selling anything!!!
Good luck with your purchase.
have a read here
<a href="http://www.pumaracing.co.uk/comp.htm" target="_blank">Leak down tests</a>
His other pages a pretty informative too, especially because he isn't really selling anything!!!
Good luck with your purchase.
Advanced
Joined: Jul 2001
Posts: 66
Likes: 0
From: Iowa
Anthony,
A compression test and a leakdown test will give different results depending on where a problem lies. A compression test will not indicate a problem with valve leakage...unless it is major. A leakdown test is the only test that I would trust to check valve leakage. Given your test results, it appears that there is some leakage around the valves.
Gary
A compression test and a leakdown test will give different results depending on where a problem lies. A compression test will not indicate a problem with valve leakage...unless it is major. A leakdown test is the only test that I would trust to check valve leakage. Given your test results, it appears that there is some leakage around the valves.
Gary
Rennlist Member
Joined: Aug 2001
Posts: 2,040
Likes: 7
From: Blacksburg, VA
Anthony:
I've internalized Bruce Anderson's position on leak-downs for 964s, so I wouldn't have had one done on a strong running engine with high compression numbers. Apparently you're familiar with why Bruce supports such a position, and know there are others (including mechanics, of course) who insist on leak-downs, even on engines that seem strong by all other measures (including dyno numbers!). I'm convinced that leak-downs will often identify strong engines as "bad", and prospective buyers will end up walking away from perfectly good cars because they think they would be a bad purchase. Unfortunately, it's too late for you to decide not to have a leak-down, you've got bad numbers, but no one knows for sure what they mean. If you'd gotten good numbers instead, you'd probably accept them as valid and reliable.
I think I'd want to talk to Bruce again if that happened to me, even though he's given the same answer many times.
I've internalized Bruce Anderson's position on leak-downs for 964s, so I wouldn't have had one done on a strong running engine with high compression numbers. Apparently you're familiar with why Bruce supports such a position, and know there are others (including mechanics, of course) who insist on leak-downs, even on engines that seem strong by all other measures (including dyno numbers!). I'm convinced that leak-downs will often identify strong engines as "bad", and prospective buyers will end up walking away from perfectly good cars because they think they would be a bad purchase. Unfortunately, it's too late for you to decide not to have a leak-down, you've got bad numbers, but no one knows for sure what they mean. If you'd gotten good numbers instead, you'd probably accept them as valid and reliable.
I think I'd want to talk to Bruce again if that happened to me, even though he's given the same answer many times.
