What should I typically expect from a compression test on a Suburban with 265,000+ miles?

Question

Basically, I just did a compression test and all but 1 of my cylinders falls between 150-165. The #6 cylinder is at 145psi. What would a brand new model of this engine run at, and what should a typical engine of this model run at with my type of mileage. I'm just trying to guage the market and see if the engine in my burb is doing better or worse than other burbs of the same year/mileage.

Answer 1

The way to use compression test information is more to diagnose problems than motor condition. The rule of thumb is to say the motor is good if all of the values of each cylinder are within 10 psi of each other. That stated though does not mean that the #6 cylinder is bad. What a compression test does is eliminate severe mechanical problems inside the motor to determine why a motor is running rough or missing. Generally speaking, motors will give a reading of around 150 psi for each cylinder when the motor is in good shape. At this high of a mileage, I would say the info from your compression test tells you the motor is in good shape although there might be a lot of carbon build up inside the cylinders.

Answer 2

I'm impressed that the motor is still running that strong without being rebuilt. Not sure what the tolerances are, especially since you didn't say what motor it is. I'd have to say that it's doing better than most vehicles with mileage that high. If you did a rebuild I bet it would last another 265k miles... Of course the rest of the vehicle might not be up to the task, but that's for you to decide.

Answer 3

WOW! Has your engine been rebuilt before? With that many miles I would expect at least 2 cylinders to be well below 95 lb. I would have to believe that your engine has lots of life in it...RUN IT!

Answer 4

You will want to get readings between 140 and 160 as the highest.... you are doing great.... keep changing the oil and keep it clean..... you should get 400K out of that engine.