# How to interpret slightly varying compression between cylinders?

I have a 99 Toyota Corolla with 255k miles. According to the service manual, cylinder compression should be 145-218 psi, with no more than 15 psi variation between cylinders. I tested mine and read 30 psi variation before adding oil for a wet test. After adding oil, compression was a bit high. The compression slowly built up after 5-10 engine strokes.

``````|Cyl.| Dry | Wet |
------------------
| 1  | 190 | 210 |
| 2  | 180 | 210 |
| 3  | 200 | 230 |
| 4  | 210 | 220 |
``````

From what I've read, the slow pressure build-up, plus the higher pressure after adding oil, indicate worn piston rings. As I don't have low compression, I don't see evidence of a bad head gasket.

What do these numbers tell me about the engine condition and/or expected time until rebuild?

Note: The car has been burning oil for a few years, and has smoky exhaust. I assume oil slipping by the piston rings is a contributing factor. Also, oil has been collecting in one of the spark plug wells.

Thanks!

• I'm inclined to think these type of specs are what you should have for a newly rebuilt engine. If that is out of spec, either you did something wrong building it or you overlooked some worn components. But they don't mean an "old" engine is going to die tomorrow if it is out side the limits. – alephzero Jul 22 '19 at 18:09
• I'm not seeing much of anything wrong with those compression numbers, either in their total pressures or in the difference between cylinders ... they look fairly normal. It surprising the manual gives an actual PSI difference. The way I'm used to seeing it almost universally is by percentage. 15psi difference at 200psi total pressure is only 7.5% difference ... I'd be okay with 20% difference between cylinders for a regular street car ... race car? Now there's something different. – Pᴀᴜʟsᴛᴇʀ2 Jul 22 '19 at 19:52