M Roadster Compression Test Results

**ShelbyGT500** · 11-17-2017, 12:11 AM

I just got done doing a dry compression test on my newly aquired 2000 M-Roadster. It has ~147,000 miles.

Cyl #1 170psi
Cyl #2 170psi
Cyl #3 165psi
Cyl #4 160psi
Cyl #5 163psi
Cyl #6 163psi

From what I read 145psi - 160psi is the minimum. To me these results seem fairly good for the age of the vehicle. Pressures are all very close to eachother. I was curious the results for some of the other Z3 & M-Roadsters.

Thanks

**Mr Bingley** · 11-17-2017, 06:58 AM

Hello and welcome. Judging by the descending results, I'd say the engine was cooling as you conducted the tests, and you started with #1. It is so hard to get good compression test results because it needs to be at temperature for each cylinder (and at the same temperature), but it takes time to conduct the test. Anyway, I wouldn't be unhappy with those results--I assume this is just to establish a baseline, and that there is nothing wrong.

**rf900rkw** · 11-17-2017, 07:02 AM

They look okay, but two things. First, at 150K, the motor is barely broken in; don't let the ad mongers convince you to treat it like a worn out GM product. Second, results from a compression test on an engine with variable intake timing is totally at the whim of the unpressurized cam control flopping about. The fact that your numbers are even says more about the condition of the vanos seal than it does the rest of the engine.

Now put that compression gauge in the dusty box with the dwell meter and the timing light and go drive the car.

**ShelbyGT500** · 11-17-2017, 08:24 AM

Thanks a bunch guys. The engine was cooling. I started the test about 1.5 hours after shutting the car off. This is just for a baseline to provide some insight on the condition of the motor. There were no maintenance records when I bought the car. Just doing routine work like replacing fuel filter, brakes & rotors, oil change, spark plugs, etc.