Cold Compression Test Results - N54Tech.com

pysical · **Cold Compression Test Results -** 07-04-2017, 08:38 AM

Just did a cold compression test on N54. I used a brand new Pittsburgh compression tester from Harbor Freight. It was a friends and he never used it.

C1 = 130
C2 = ~127
C3 = 130
C4 = 130
C5 = 130
C6 = 130

I have read that they are usually around 160+. Should I get the engine warm and try this again? Or should I rent a compression tester from Autozone and try to see the difference?

NorCalN55 · 07-04-2017, 09:13 AM

Readings with the engine warmed up seem to be a better representation. As for the low values, does your gauge have the Schrader valave at the gauge or the end of the hose you thread in to the spark plug hole? If the valve is at the gauge then you will lose some psi between the cylinder and the gauge due to expansion in the rubber hose. You will get a more accurate reading using a gauge that has the valve at the tip of the hose, not at the gauge.

That said, you probably didn't lose 30 psi in the hose so hopefully you have better readings with a warmed up engine. Good news is all your values are close to, or the same.

pysical · 07-04-2017, 09:15 AM

Did a walnut blast about 7k miles ago. I just got the engine up to 180 degrees and tested cylinder 1. It came back 135. Do I need to go warmer?

NorCalN55 · 07-04-2017, 09:47 AM

Probably not. How long did you let it crank before you checked the gauge? If you let it crank 10 times and you still don't see improvement, then do a leak down test. You can also pour an 2-3 ounces of oil in the cylinder and retest...wet compression test. Doing a wet compression test before the leak down test will impact the leak down test results because the added oil can cover up potential locations for an air leak.

pysical · 07-04-2017, 10:03 AM

Quote:

Originally Posted by NorCalN55

Probably not. How long did you let it crank before you checked the gauge? If you let it crank 10 times and you still don't see improvement, then do a leak down test. You can also pour an 2-3 ounces of oil in the cylinder and retest...wet compression test. Doing a wet compression test before the leak down test will impact the leak down test results because the added oil can cover up potential locations for an air leak.

I let it crank for about 8-10 seconds. I watched the gauge and after it didn't move for about 3 seconds I stopped.

I used my air compressor to test the gauge and the gauge might be reading about 10 psi to low. If all cylinders are pretty much identical, but just all low, what could be the issue?

ShocknAwe · 07-04-2017, 01:00 PM

Since all cylinders are about the same, I'd try another test kit to be sure before jumping to conclusions.

limitdown · 07-04-2017, 08:43 PM

Test it again warm and with another compression tester.
There's not much variance between the cylinders. When there's an issue, it's usually only the bad ones that are way off from the others.

ianc · 07-06-2017, 04:36 PM

Quote:

Since all cylinders are about the same

This. You're looking for a significant variance between any two cylinders. If you're not burning oil and don't seem down on power, I wouldn't stress over it...

ianc

Rob@RBTurbo · 07-06-2017, 04:57 PM

As there is so much consistency (albeit fairly low results) I'd initially recommend trying another compression tester as some have poor fittings that don't seal well. Or better yet perform a leak down test.

mhigham · 07-07-2017, 10:13 AM

I'm guessing your gauge is just low. It would have to be a very large failure to affect them all. If it's still running under its own power and not smoking, I'd call those results good. They are all even, which is a good sign.

Did you have the throttle body open? How does it run?

pysical · 07-07-2017, 02:30 PM

Well I think this post is done. I am starting to lean towards just getting the engine built. Molnar Rods with CP Pistons. Then probably going to get a port job on the head by a local company. Going to also probably run GC turbos. I won't be doing this for another month but I will make a post with some pictures of the progress.

LessIsMore · 07-07-2017, 02:43 PM

Hmm, based on this thread alone, seems premature to tear down the engine. Looks like your engine is probably healthy. Personally, I'd let it ride until an actual issue/symptoms came up.

pysical · 07-07-2017, 02:55 PM

Quote:

Originally Posted by LessIsMore

Hmm, based on this thread alone, seems premature to tear down the engine. Looks like your engine is probably healthy. Personally, I'd let it ride until an actual issue/symptoms came up.

I want to go with some GC or GC Lites. The torque I will be making will just break the engine quickly anyways. All this labor is going to be free so I might as well do it right the first time.

danas · 07-10-2017, 06:35 PM

As long as all readings are close together I wouldn't worry about it. Too many variations.. gauge itself.. engine temperature, battery charge etc..

Just to make sure you had all the plugs out when performing the testing ?
Also idkn if that's possible in our cars with throttle controlled by wire, but normally you would have to hold the throttle all the way open.. Fuel pump fuse out too

victor247 · 07-14-2017, 06:19 PM

I did a compression test about a week ago and had the same values. They were 130 across.

TomasE82 · 04-10-2019, 04:34 AM

Hi All,
So what happened im having the same problem. My comp/tester is new but the valve is at the gauge. I'm getting the same readings I did the test all wrong engine cold didn't push the gas pedal down. Also the first time i did the test i didn't remove the fuse for the fuel.

2009 135is E82