1997 850 T5 Low Compressions

[MNCO1]

So I compression tested my car today. Didn't have any engine lights. The car seemed to run fine although I burn a little oil. It was about mid 60's F today and I live at 6200'. Not sure what influences the testing. Anyway, got 130 psi across the first 4 (from passenger side) and 120 something on the 5th. A little shocked as I had been babying this car. Never did a compression test before. I had the car since 2003 and it was then 84,000 miles. Its now 150,000. I expected something closer to 185 psi but certainly over 156 psi. I wet tested the second and third cylinder (from passenger side) and got 208 and 290 something. So I guess the rings aren't up to par?

I did wonder though if altitude has anything to do with compression testing? Any suggestions on my low performing cylinders?

[rspi]

It shouldn't. If you added to much oil it could cause the outrageous wet reading, or your gauge might be off.

Did you do it warm and at WOT?

Also, if you don't mind sharing, what type of oil do you use and how often do you change it?

[MNCO1]

I screwed up on the test. It was dead cold. Got below freezing last night. Too much oil on wet test too. Thanks. Anyway, I have been doing full synthetic 10w30 Quaker and changing it every 3000-4000. I over do it. Thanks

[erikv11]

Agreed, altitude will not affect compression testing.

Even if you screwed up the test, the tight grouping of your first set of readings looks encouraging. Give it another test sometime, the white blocks are super durable and with your short OCI I bet you will be pleasantly surprised by the compression readings.

[rspi]

Please redo it and post the good numbers. You can skip through to about 9 minutes.

1. Warm the car.
2. Disconnect the fuel supply.
3. Disconnect ignition.
4. Pull the plugs.
5. Finish the test.

[MNCO1]

Well,
The weather was nice and I wasn't sick with flu so I redid the test. Drove around alittle to warm the engine. It was just over 200 degrees F. I was surprised that my numbers didn't change. 130 psi first 4 cylinders,left to right and 126/127 psi on the right most cylinder. The grouping looks nice but the numbers are still low compared to what I was expecting. Could be a bad gauge I guess too but it duplicates the readings from before. Makes rethink whether I want to hang onto this car or what I would put into it from here on out. I haven't had any problems starting or running. No codes. Full synthetic oil. Do cylinders just lose their compression over time? 150,000 miles. Should I look around for a new or rebuilt engine? Its my daily driver, 20 miles each day. I don't take it across country. I guess it could keep running just fine for another 10 yrs.

[socompsp]

my motor in my 98 c70 has 185psi in each cyl. it has 211,000 miles. its all about who has taken what kind of care for it for how long. as far as keeping it, it depends on the reason you are getting these numbers. "new" used motors are not hard to come by and are almost considered cheap. so it depends on the condition of the rest of the car when i personally would choose to scrap it or not.

[MNCO1]

185. I was hoping for that. Don't know the history of my car for the first 84,000 miles, apparently it wasn't good enough. I am curious how I have had this car 10 yrs and have accepted how she drives. I am assuming she doesn't have quite the performance that it could have. The rest of car is in great shape.

[phils94850]

I ran into the same issue with a 97 850R I had, the car ran perfect but, I had it dyno'd and it really wasn't performing as it should, come to find out the compression was down on all cylinders similar to yours in the 130s or so. As said.. a new/used engine is easily to come by and youll have a beast again.

[rspi]

Thanks for redoing the test, sorry to see the numbers low.

Did you do a wet test? That will tell you if the gauge is bad or the cylinders are worn. If you jump from 130 to 185 like mine did in the video, you will know it is the cylinders.