confused by Leakdown test

**GTV67** · #1 (**permalink**) 10-23-2009, 09:14 PM

I have a 2000 engine out of the car that I am about to tear down to do some more head work.

A few weeks ago, when the engine was still in the car, I warmed it up and did a compression test - all was well with 190ish on all cylinders and good uniformity.

I didn't have a leakdown tester at the time, but now the engine is out, I have one, and I tried it today with the engine on the stand.

So, I bring number1 cylinder to TDC, pressurize the cylinder and...instant loud roaring leak sound. I can hear the air leaking into the crankcase, confirmed by listening at the dipstick tube. I can pressurize it to about 25psi and it leaks down to zero from there in about 3 seconds.

I know you're supposed to do leakdown testing on a warm engine, but that's not an option right now - so is this typical on a cold (oil drained 2 weeks ago) engine? If so, is there anyway to do a meaningful leakdown test on this engine?

What other ways are there to check ring-sealing and general health of the pistons/rings/liners?

Thanks,

-Richard
Scotts Valley, CA

**Gordon Raymond** · #2 (**permalink**) 10-23-2009, 11:09 PM

If you are tearing this down (completely?), the best answer will show at that time.
As you probably know, the leakdown test is just that. In a warm engine, that has run recently, rings are seated on a film of oil, both on the liner, and in the ring grooves on the piston. Depending on the type of piston, if it has an expansion control insert, warm, it will be round, cold, oval. I have seldom had the same leakdown readings on warm and cold engines, though in some cases, compression tests on cold engines will come close to warm, with the same cylinders showing low.
Again, as the engine is being torn down, your critical analysis will be visual and possibly measurable when it is apart. A close examination of pistons / rings and liners disassembled will yield your answer.

dancia · #3 (**permalink**) 10-23-2009, 11:47 PM

I wouldn't get to excited about it. If the compression was good and the blowby was ok or blue smoke wasn't evident under acceleration, It's probably fine. But, the engine's out now. Check bore, hone and re ring if you're concerned. Or the full nine yards if you're a warplane kind of guy.

**Alfisto Steve** · #4 (**permalink**) 10-24-2009, 06:56 AM

Leakdown tester we have had error in directions and we found out to work correctly our tester requires you do not exceed 10 psi input pressure (directions said 100 psi max and that was a typo).

You have to read leakage in % on second gauge while holding input pressure at 7-10psi on first gauge.

**GTV67** · #5 (**permalink**) 10-24-2009, 03:05 PM

Thanks to all who replied.

I decided to take the advice and not worry about it too much - The head is off as of 30 minutes ago. This is an engine with about 2000 miles since a complete rebuild - it's really out because of transmission problems - but I've decided more zip at the top end would be nice seeing as it's out. Therefore seems like the right time to be investigating everything I've worried about since I built it, and making sure before improving porting and cams etc.

It did seem to use too much oil, but no blue smoke was ever emitted, either under acceleration or deceleration - and it didn't leak (much) and the coolant has no oil in it - so I'm just trying to do some detective work.

Steve, it sounds like we have the same leakdown tester (Harbor Freight ~$30...?) whose directions do say to raise the input pressure to about 100psi. Maybe I should get a better one because I'll always worry now that this is giving me false numbers.

Thanks again,

-Richard