Compression Testing Correctly and Cold vs Warm engine

[ProwlerGT]

BUMP - No one knows the answer on this?

[Turbo Powered]

Originally Posted by ProwlerGT

I know proper procedure is to remove ALL plugs before doing testing, but is that just because the manual wants you to test all cylinders or because it changes the pressure results?

I ask cause I'm about to test the front bank after I take the car for a spin and of course I would rather not remove all the junk to test the rear bank again if the car seems to be running fine.

The plugs are all removed so that the starter motor is only having to compress the air in one cylinder. The engine will turn over slower with some of the plugs installed, so the readings will be slightly lower.

[ProwlerGT]

Originally Posted by Turbo Powered

The plugs are all removed so that the starter motor is only having to compress the air in one cylinder. The engine will turn over slower with some of the plugs installed, so the readings will be slightly lower.

Thank you. So when ya say "slightly" do ya think thats like maybe 5 psi lower? lol - I know I know.... i should just do it right, but it really would just be only for the sake of the test cause I "think" the engine is running right.

[oohnoo]

Just do the test already, it's only a compression test. Make sure you have a battery charger on it cause if your battery isn't healthy it'll slow down which will result in slightly lower numbers.

[ProwlerGT]

Originally Posted by oohnoo

Just do the test already, it's only a compression test.

I know I know huh? lol ok ok - I just didn't want anything all skewed to happen.

[HLxDrummer]

I was just wondering this SAME exact question, how convenient lol

Anyhow, we tested the compression on the VR4 that hasn't ran in a few weeks (so it's obviously cold and no oil pressure). Most cylinders were around 115 and one was slightly lower (5-10psi off). I was hoping the warm figures would be a decent amount higher since these are kind of low (service limit).

How are you guys getting 150psi cold!? lol

From my research it seems that from warm to cold there is a difference of around 10-15 psi but I have no hard proof, just from what I've read.

[ProwlerGT]

Did the warm compression test earlier on the front bank:

Cylinder 1: 184
Cylinder 3: 180
Cylinder 5: 179

Will post the remaining bank later.

As you can see so far testing warm vs cold can variate greatly and really doesn't show a pattern (refer to post#8 for cold test #s). The idea that it'll only be 15lbs difference or any set psi difference is just false. Just gotta do the test correctly. I wasn't even comfortable doing the test warm without the 3 rear plugs out, instead I just removed all front plugs.

I'm probably going to retest again all 6 once all plugs are out and its warm. Would've done it all at once earlier, but had a friend stop by and supper and tonight the NEW ORLEANS HORNETS are playing in the semi-finals so car will sit !!!! lol

[oohnoo]

See, nothing to be afraid of........Great results.

[ProwlerGT]

Originally Posted by oohnoo

See, nothing to be afraid of........Great results.

LOL - I just hope the rear bank is just as good and I have a hunch it will be.