HEllo,

I have an o5 S60 checking compression I come up with 140 ( 5 seconds of cranking) the first time and then once I check again it comes up with 160psi the second time 5 seconds of cranking , why is that, pressure is released after each test, all cylinders show the same compression and same results 2 different reading first and second time.

I had a low oil pressure light come on so wanted to check compression

 

Are all the spark plugs out when you're testing one cylinder??

I had to get 10 or 11 "cranks" in order to reach max compression of ~212 psi in my engine.

And I'm not sure what typical compression tester gauges (with rubber hoses) go up to, but I bought this fancy tester kit to make sure it could handle anything I threw at it....
I actually overtightened it in the second or third plug hole... and the "hose" came loose, but I somehow managed to get the hose to grip back and unscrew from the other part that was in the block, then used a spark plug socket to get the other part out. The threads on the block were slightly corroded since I'm guessing my engine hasn't seen fresh plugs in close to 10 years. Should have used some anti-seize. Anyway, I tried using my older compression tester with rubber hose and rusty threads... but I couldn't get that gauge to register above 140-150 or so. It also didn't even hold compression either, so I was forced to keep using the new Equus tester... just had to be way more careful when tightening it down. Might consider sending it back to get one with hose clamped on a bit tighter, but yea....

 

You likely did NOT do the test properly. Look over these proceedures and go from there. You should do it with a warm motor.

Compression Test - Volvo S70 GLT, 1998

 

Do you have the procedures for a 2007 s40?

 

its pretty much the same for all cars. The pain is with the newer cars you need to get the coils out of the way to remove the plugs.