Please explained compression test readings

Joined
Jan 23, 2014
Messages
533
Location
Australia
I just performed a compression test on my 6G74 2003 Diamante. Readings:
  1. Cylinder 1, 151 psi dry, 162psi wet
  2. Cylinder 2, 151 psi dry, 179psi wet
  3. Cylinder 3, 150 psi dry, 174psi wet
  4. Cylinder 4, 150 psi dry, 181psi wet
  5. Cylinder 5, 151 psi dry, 190psi wet
  6. Cylinder 6, 150 psi dry, 180psi wet
Can someone tell me: 1. Is 150psi dry too low? 2. Dry tests are surprisingly even, but wet tests are surprisingly uneven, what does this mean?
 
Joined
Oct 7, 2012
Messages
3,004
Location
NYC
Did you use an even amount of "wet" for each cylinder? What'd you use? ATF? Thick engine oil? I'd be inclined to redo the wet test.
 

Spetz

Thread starter
Joined
Jan 23, 2014
Messages
533
Location
Australia
I just used my 5W40 oil (Shell Ultra) Fairly even oil added to each cylinder. I re-did the lowest cylinder thinking maybe I did not crank it long enough but it still came up at 162psi
 
Joined
Oct 21, 2011
Messages
2,021
Location
CA
Do a leak down test which is a better method. But those would be considered acceptable for warranty or defect purposes. Not that bad. Lowest is 85% of the highest and 90% of the mean. Are you burning oil? Was your test just curiosity or do you have a problem? How many miles/Km?
 
Last edited:
Joined
Dec 19, 2004
Messages
7,430
Location
beaver land EH?
you must keep the throttle wide open (as andyd said). you must consistently wet all 6 cylinders with the same amount of oil (e.g. squirt 2 oz or so (approx 60ml) you must crank (turn over) the engine the same amount of rotations on a 6 cylinders in order to get as consistent of a reading (across a 6 cyls) as possible. If your wet/dry reading deviates for more than 8~12psi per cylinder, that cylinder's piston ring (top and 2nd compression rings) are worn. While it may not be at the late stage that leads to oil burning (minimal), it's still a sign that the piston rings have seen quite some service life, and in need of replacement. also consider the sealing conditions of your intake/exhaust valves. If they are leaking, wet/dry compression reading remains almost the same but the cylinder compression remains low....this can also be verified (engine put in place) with one of those spark plug hole pressure line adapter (connect to your air compressor) while the valves are at TDC...listen to intake or exhaust manifold and see where the hissing sound coming from. Q.
 

Spetz

Thread starter
Joined
Jan 23, 2014
Messages
533
Location
Australia
Throttle was not open, but intake manifold was off. I poured about 7-9ml of oil per cylinder. 60ml seems like too much?? I used a 10ml syringe for this so oil amount was consistent. Engine has 122K miles I did the compression test as after some maintenance I was worried I had bent a valve. EDIT: Car was burning oil and I just changed the valve stem seals. Not sure if it burns oil currently, and this is why I was thinking I may have bent a valve
 
Last edited:

Spetz

Thread starter
Joined
Jan 23, 2014
Messages
533
Location
Australia
I warmed up the car for a bit before doing the test. The engine was warm, but not at full operating temperature of course
 
Joined
Dec 31, 2009
Messages
898
Location
Santa Cruz, Ca.
What is your symptom? If your engine runs fine, there is no problem. Those numbers don't look bad, but I'm not sure you did the test right if you didn't open the throttle.
 
Top