[DGR-Z246-98]

Hi All,

Need the teams input here again thanks to the suspect mechanics in Dubai!!

Since the re-build last year, I've noticed a light layer of oil behind the bench seat in the engine compartment after running WOT.

Certainly no major leak, but I was pretty sure that it was hitting the belt somewhere and causing the film on the bulkhead.

I asked the shop to look at it last time she was in for a service and they told me that they had replaced a couple of hoses that were worn and saturated and that it was fixed, however once back on the water no change.

I've started to get a build-up of oil in the bilge and have had to give her a top-up ever so often, so decided to give the shop another go (VERY limited choice out here!).

This time they told me they had fixed a problem around the oil filter assembly, seemed plausible for oil hitting the belt, but a test run resulted in some oil around the starboard engine mount and in the bilge, so back to the shop.

So here's my problem, when I called them yesterday to check on progress they told me that they had found that under load the engine was forcing oil out of the dipstick, and that according to their mercruiser manuals this meant that there was a problem with the piston rings and that the engine needed an overhaul.

Aside from the fact that i'm less than a year into the rebuild (re-bored, new rings and piston heads - so should be good) the actual diagnosis didn't seem to make any sense to me. I can understand that by fixing the other leaks they have increased the pressure somewhere else, but how could a problem with the rings create more pressure?

Have not been able to find anything similar on the threads or interweb, any ideas anyone?

Steve.

[WetWilly]

Hi Steve,

Oil being forced out of the engine via the dip-stick tube would indicate an extreme amount of internal pressure inside of the motor. This would have to come from either blow-by from the piston rings or from worn valve guides. The funny thing is, your motor should have a vent hose on the top of the vale covers to vent this "blow-by" back into the carb or throttle body. If you have a carb, check your Spark Arrester for signs of excessive oil from the vent hose and if your Injected, check the hoses and the intake where they attach for oil.

Before opening up the motor, I would check the piston rings by doing a "Dry" compression and bleed down test on all 8 cylinders and recording the readings, then perform the same tests "Wet" (adding about 30cc of oil to each cylinder via the spark plug hole). This will give you a good indication of how well the rings are working.

I would clean the motor to remove any oil on the outside, then wrap and secure a rag around the dipstick/tube and run the motor under load again. Now if you find oil again, try to trace it back to the source and the rag will tell you if it's really coming out from the dipstick.

Good luck,
WetWilly

[DGR-Z246-98]

Many thanks WetWilly, I have suspicions around the vents and the PCV being hooked up correctly from the rebuild so will check that, just trying to see if I can get anyone to do a compression test.

Will update the forum with what I find,

Cheers,

Steve.

[dwmax]

Wetwilly is correct, I had this same problem on a car I had and it turned out to be a clogged breather hose on the valve cover, it was causing to much pressure inside the motor and the only escape was out the dipstick. So I replaced the hose and cleaned the valve cover internally and replaced the pcv valve and it never did it again good luck and hope this helps. lets hope that is all it is and not bad rings or valves.

[DGR-Z246-98]

Thanks Darrell, helps back up my theory as everything else was new last year, keeping my fingers crossed!

Cheers,

Steve.

[DGR-Z246-98]

Had the mechanic down for the compression tests today and he found oil in each of the cylinders. Guess that means it's the rings then.

Strange that she's running so well at the moment, would have though there would be some sort of performance drop, smoke, high oil usage etc... ?

Just waiting for the quotes

[Dredd]

Yeah, seems like you would be seeing smoke... but maybe not if you don't have through hull exhaust.

FWIW... I've always noticed that all my toys seem to run best right before they break. I keep everything in great running shape but I will admit that when something seems to be running a little extra awesome, I usually start getting nervous.