Compression test results - one cylinder low

[ukflyboy]

Hi all,

Been a bit late getting the car back on the road this summer and did a compression test. Five of the six cylinders (S3) were 11.5-12.5 bar (~167 - 180 PSI) apart from one which was sitting consistently at 10 bar (145 PSI). Is it worth taking it somewhere for a cylinder leakdown test?

[GreenV8S]

That difference is enough to indicate a problem, and if it's consistent then it needs further investigation IMO.

[Panamax]

T'internet suggests,

"If you find one or more cylinders are below the 10 percent range of the others, squirt a little oil down the cylinders and try again. If the pressure comes up significantly, the problem may be worn piston rings. If the pressure does not come up on retest, the issue may be with the valves or the head gaskets."

[NicBowman]

Hi, also might be worth checking valve clearances. Particularly on the low pressure cylinder.

Previous tip, to add oil, is first port of call though.

Personally I wouldn’t panic either way. If oil does increase the pressure, still ok to use the car. Will go for miles still, maybe look in the winter.


Nic

[ukflyboy]

Thanks all, I completed a wet compression test and the pressure went up from 10 to 11.7 bar, so may well be the rings. I'm finding that it is down a bit on power and perhaps hesitates a little under load (or maybe I'm just being neurotic?!). Likely to be connected?

[LLantrisant]

imo nothing realy to worry about.....i would only worry if it would be down to e.g. 6bar.

as long as the engine runs and doesnt consume too much oil or smoke.....leave it like it is.

what you could do: check valve clearance, but only if this type of V6 doesnt already have hydraulic lifters.

see it from a different view:

as long as a car runs well, why somebody would do a compression test?

i guess your car is running well, but your (un-necessary) test has now made you unnecessarly worry about.

Edited by LLantrisant on Saturday 25th June 08:29