Re: [Amel Yacht Owners] Re: The mistery slick
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The quickly oil resoaked air filter is also making me think that engine oil could be causing the oil spots on the water. A simple test to check to see if the engine oil is coming up from the tube that vents the crankcase is to decouple the tube from the intake, place it in a bucket and run the engine briefly and see if you have oil spatters in the bucket. If you have a lot of blow by from the crankcase you will also see what looks like exhaust coming from the tube, which hopefully will not be the case since that may mean that you have more serious problems. I am not familiar with the exact crankcase ventilation system on your engine but most systems also incorporate a drain back systemso that much of the oil blown into the engine intake from the crankcase ventilation system can drain back to the crankcase. If the drain back system is not not functioning properly, oil can pool in the intake system and be drawn into the engine.
It sounds like you have been pretty meticulous with your engine maintenance so hopefully this turns out to be something simple.
Best of luck,