Compression/Leakdown testing - must engine be warm?

[SadbutTrue]

I bought a leakdown tester (well, something I'm going to turn into one, anywya) last week with the intention of doing a compression and leakdown test on my engine, which has been torn down for 2+ months. I was all set to get started when I noted the web sites I was using for guidance said that for both tests you need to have the engine warm.

So yeah, I'm basically wondering if its worthwhile to do the tests now or if I should put it together, fire it up for a few minutes then do ithe tests.

 

[socalwrench]

generally, yes, the engine should be at the normal operating temperature. this eliminates any possibility for variation in regards to piston material (expansion) and piston ring design (IE gapless rings).

since the engine is not in the car, or in running condition- you can still perform the leakdown test. just prime the oil system and rotate the engine by hand several times. this should get some oil up the cylinder walls and into the heads.

 

[mrmustangman357]

isnt your engine still in the car? Just make sure the oil is on the cyl walls as suggested. up at operating temp really isnt too important. you are mostly looking for variation cyl-to-cyl so everything is equally loose.

 

[jlangholzj]

i was gonna say, compression checks are pretty routine and mandatory in planes, and If we can't get up to temps, we just squirt a little oil in each cylinder before the check. do that same and you should be fine.

 

[SadbutTrue]

isnt your engine still in the car? Just make sure the oil is on the cyl walls as suggested. up at operating temp really isnt too important. you are mostly looking for variation cyl-to-cyl so everything is equally loose.

Yeah, engine's still in the car. So just squirt some oil in the spark plug holes and go for it? And should I still run both tests?

 

[CraigMBA]

I'd do it dry first. If you have a problem, you'll find it dry.

 

[rbohm]

i agree with craig, do it dry first. if you get any strange readings, then do a wet test as that gives you a base to determine where any issues might be. as for temperature, the engine doesnt have to be at operating temperature to perform these tests. the numbers might be slightly lower cold than warm, but they will be the same percentage lower across the board and thus a non factor.

 

[SadbutTrue]

Is there any downside to squirting some oil in?

But thanks, hopefully should have something tonight.

 

[CraigMBA]

If you find a problem dry, you can squirt it and see if it helps. If it does help, apart it comes.