2006 S60R Misfiring, poor compression, oil/carbon on pistons

[IVIUSTANG]

Hey all!

I am the designated mechanic on my friends 2006 S60R(with 180,000 miles) and am a little bit stumped, here goes!

For the past couple months it has been misfiring in cylinders 3 and 4. I have replaced all plugs and coils; no big change. He has also had some goofy issues with coolant, as the car heats up it seems to disappear out of the reservoir, if the coolant cap is taken off the coolant magic returns. If the cap is left off for long enough the coolant "permanently" never returns. Also, most of his misfires seems to happen on first start of the day and tend to taper off as the car warms up. I have done combustion gas tests and coolant system pressure testing on the car with no problems found.

Tonight I did a compression test on all the cylinders and 120 PSI in cylinder 1(A known non-misfiring cylinder) 100 in cyl 3(A known misfiring cylinder, and 120 PSI in cyl 4(A known misfiring cylinder) I know these readings are 30-40 PSI below the minimum of a healthy engine.

Cylinders 3 and 4 are caked in carbon and maybe even a little oil, and I found cylinder 4 had ZERO plug gap for some reason; I regapped this plug. Cylinder 3 gap was perfect.

I did the PCV system on this car last year and the intake valves were spotless. I also have cleaned and reinitialized the ETM within the past few months and reininstalled with a new gasket.

I am wondering if it's possible the headgasket or exhaust valves could be an issue on this car; it doesn't consume any oil or coolant(if the cap is taken off periodically) I am stumped, and am wondering if an S60R is even worth taking the head off with such low systemic compression?

Any advice would be appreciated!

Thanks,
Jesse

[abscate]

All the signs of bad head are there...bad compression, coolant usage, carbon caking.

You could have multiple issues of course. My guess is valve seats failed, which stressed cylinders, warping head, carbon deposited, coolant leaks..in order of progression.

But that's a guess..time to get the head off!! Full valve job probably.

Make sure you add oil to the cylinders and retest compression to evaluate ring performance before you take the head off

[IVIUSTANG]

Two days of driving later since regapping the plug and no more misfires, just a long term fuel trim code that came back after everything was cleared, checked for intake leaks and also looked at physical condition of front O2 sensor; both appear ok. Give it more time, or any other suggestions?

When I did the compression test he said the engine was hot... but it had actually been sitting for 4 hours and was only warm; so that could be part of the low compression readings.

Jesse

[abscate]

Retake the compression readings warmed up and then again with oil in the cylinders.

No sense throwing parts at an engine with bad compression, you won't move forward.