4 replies to this topic

[Keith Novak]

Does anyone have data that shows the difference between leakdown results with the motor cold vs. hot? I've always done it hot but heard some say the difference is negligible.

I tried to do this experiment last night before I pull my old engine using 2 different leakdown tools to also compare the tools but 2 cylinders seem to have nasty valve problems (massive leakdown) so I didn't even want to get the engine hot in order to save whatever good parts are left in this engine.

I figure this info could be useful in testing used engines or different heads while the engine is out of the car. I figure it's not much use on a brand new engine since the rings aren't set yet.

Thanks,
Keith

[dstevens]

The reason you want it warmed up is so everything will seat as it would under operating conditions.

[Keith Novak]

The reason you want it warmed up is so everything will seat as it would under operating conditions.

Agreed, that's why I've always done it hot. This came about when I did a leakdown months ago a used engine I bought, and found much better results than the previous owner. I'm not sure whether it's because we used different tools, he did it cold and I did it hot, intake stroke vs. compression stroke, or maybe my leakdown kung-fu is just better than his. I figured I'd test a few possible theories but since then 2 cyliners have gone to hell.

If it's 1% difference cold vs. hot, that would be good enough to say this motor or head sitting in my garage isn't runnoffs strong but still not too shabby. It's a bit better than the test shows since it's cold and that doesn't require installing it and breaking it in first. If it's >10% like the difference between our measurements, it wouldn't be very meaningfull cold at all.

BTW- I think I unintentionally did this as a poll, not a normal thread?

[FTodaro]

I did a compression test cold before I remembered I had to do it hot and the numbers hot were like 30% better hot.

[Keith Novak]

That's what I was looking for. Thanks Frank. Sounds like a couple % difference will get lost in the bigger difference between tollerances cold vs. hot.