Leakdown / Compression Question

NewPorsche91132 · 03-23-2016, 09:28 PM

Looking at a 68 912. Compression came back 172 across both banks. Leak Down was 29%

How bad is that leak down number? How does that compression number look?

dad911 · 03-23-2016, 09:36 PM

Ugg. I cringe whenever I read about leakdown reports like that, because it isn't the whole story. Leakage of 29% is excessive, and mechanic should have told you what is leaking, intake, exhaust, or crankcase. Also, is it 29% across the board, or was that the worst cylinder?

If he is saying all cylinders are exactly 172/29% I'd say tend to think report is BS.

T77911S · 03-24-2016, 03:36 AM

172, I would drive it and not be too concerned about the leak down.
I would think it would be hard to get 172 with a 29 leak down.
just my opinion, I don't or have not done a lot of leak down, just compression

dad911 · 03-24-2016, 04:28 AM

Quote:

Originally Posted by T77911S

172, I would drive it and not be too concerned about the leak down.
I would think it would be hard to get 172 with a 29 leak down.
just my opinion, I don't or have not done a lot of leak down, just compression

I took this to be a PPI not an existing car......

tharbert · tharbert's Garage

I think the important result is that the pressures are even across the cylinders, not the actual number. In any event, I'm no expert but doesn't 172 psi sound high?

yelcab1 · 03-24-2016, 08:12 AM

I don't think you can get 172 psi from a 912 engine. The compression rate is not that high. Secondly, if there is 27% leakage, it would be hard to get 172 psi from that cylinder.

The evidence is not complete but as it is right now, it points to a test performed incorrectly.

Avanti · 03-24-2016, 05:32 PM

Quote:

Originally Posted by dad911

Ugg. I cringe whenever I read about leakdown reports like that, because it isn't the whole story. Leakage of 29% is excessive, and mechanic should have told you what is leaking, intake, exhaust, or crankcase. Also, is it 29% across the board, or was that the worst cylinder?

If he is saying all cylinders are exactly 172/29% I'd say tend to think report is BS.

In my years of wrenching and instructing, I've used multiple brands of compression and leak down testers and run across more than a few bad testers. I'm always suspect of any tech's test results when a Harbor Freight tester is used. Yes, some "⎌Pros" use cheap tools.