Just did a compression test

[geoff c.]

I have a 1994 Mazda B2300 and I noticed last week that I have been using about a quart of oil every 250-300 miles so I decided to do a compression test to see if it was my valve seals or rings.
Well here are the results:
Cylinder 1: 150PSI

Cylinder 2: 140PSI

Cylinder 3: 120PSI Dry/ 150PSI Wet

Cylinder 4: 145PSI

Looks like my rings are shot in cylinder 3, that also explains my rough idle.
Also about a month ago my engine knocked on start up but it only happened for about 10 seconds on one day. Then a week ago my engine started knocking again and did so for about 2 minutes but it hasn't come back. I sea foamed the engine Monday also.

 

[scotts90ranger]

Compression should be closer to the 180psi range... looks like #3 might have some issues though.

 

[RonD]

Yes, the dry and wet PSI tells the story.

How many miles on the motor?

 

[PetesPonies]

First of all, that does not tell you that you have bad rings. It only shows you have lower compression in that cylinder. I would bet it more of a valve sealing condition than ring problem, but that is just an educated guess. You want compression to be within 10% in all cylinders. That means you should be between 135-150 . . . not 180. If they all were within that, you would be fine. I know your compression came up some with oil, but that's normal. Did you add oil to other cylinders and take a reading? The slight compression loss you seem to have is not responsible for a quart of oil in 250 miles.

 

[geoff c.]

Yeah I know the compression should be within 10% of each other for it to run smoothly. It may have been 180 when it was new but not now. I only did a wet compression in the one cylinder that was way lower than the others. The motor has 177,000 miles on it. I can't afford to do anything about it right now because I'm getting married in a couple of months and have other expenses so I guess I'm driving it like this for a while.