I would appreciate your input on my high mileage (225K) DD. I was thinking about putting some money into getting the AC working but first decided to have the compression checked. My usual mechanic measured at 95-110 psi accord the 4 cylinder.

According (no pun intended) to Haynes the factory spec is 178 with a minimum of 135. Does this mean my engine is on its last legs? I don't notice any major runnability issues. Can it continue to run at the low levels for a good while? Will compression usually just gradually taper off over time as the rings/seals wear and I should just not worry about it? AC or no AC?

They checked each cylinder twice and this is a reputable shop so I assume the readings are accurate.

Thanks
Matt

Time for some: http://www.auto-rx.com/

You can read about it on: http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=postlist&Board=5&page=1

Or it maybe easier(also cheaper) to use or top off with some Mobil 1 High Mileage oil. These are good stop gap measures prior to tearing the engine apart.

Actual readings are not important as long as all cylinders are within 15% as yours are. The readings can vary depending on many factors such as warm vs cold engine, throttle open or closed, type of compression gage, number of compression strokes during the test, etc. You just need to be sure to test each cylinder the same way. I would say your engine compression is fine based on the results.

I agree it is most important that the readings between cylinders are very close, (within 10% of each other is ideal).

Typically, if all cylinders are well below normal, it would indicate wear either in the cylinder walls, or the rings (or both). If you have a lot of wear causing low compression, you should be noticing an odor of gas in your engine oil when you change it, or when you check it. A good way to check and see if there really is a significant amount of wear is to do the compression test, then squirt a bit of motor oil down the spark plug hole, and test again. A significant increase (more than just a few PSI) in the second compression test would indicate that there is a good bit of wear, and the motor oil helped to seal the rings up for the second test.

In a high mileage engine, you should expect some amount of wear on the cylinder walls, and rings, it is normal. As long as the readings are within 10% between cylinders, it is normal wear, and you can continue to drive it. It might not make quite as much power as it did when it was new, but there isn't anything drastically wrong with it.

Thanks SS,nh & TQ for your quick responses. The low the compression is definitely very consistent so that makes me feel better about the results. The car drives fine so we'll keep on rollin'. Looking forward to spending some more time on DA. Matt