Rotax 912UL oil overflowing. Why?
in 912 / 914 Technical Questions
12 years ago
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Re: Rotax 912UL oil overflowing. Why?
by Arthur Götz » 12 years ago
Thank you, Mark, your explanation clears up a lot of misunderstandings I had about the gurgling question. One more: If you gurgle you're emptying your oil suction side. Why would you want to do that? Surely the engine is lubricated quicker after start-up with the suction piping filled?
I replaced the oil, oil filter, fuel and fuel filter. I checked the pistons and sleeves as well as I could through the spark plug hole. Which wasn't really very good. There is a thin layer of deposits on the cylinders, but it looks like it is coming off, instead of being a result of the diesel. The spark plugs look brand new. After 27 hours I would have expected them to look worse. The test flight was perfect, with everything, including my confidence in the engine, in the green.
Blue skies
Arthur
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Re: Rotax 912UL oil overflowing. Why?
by MARK JACKSON » 12 years ago
Hi Arthur
When you gurgle you are pushing any oil that may have collected in the crankcase back into the oil tank. You are also pumping oil from the oil tank into the engine, so effectively you are filling the suction side oil hose and pressurising the oil system, although that is not the reason, its a good thing.
If your oil tank is above your engine, when you stop the engine, the oil can syphon back into the crankcase and possibly fill the cylinders with oil. If that oil gets past the rings then you will damage the engine if you tried to start it because of hydraulic locking of the piston.
Some times people have to remove the bottom spark plugs to turn the engine over and get the oil out. This only happens with badly designed oil systems though.
Mark
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Re: Rotax 912UL oil overflowing. Why?
by Geoff Bell » 4 years ago
Once again Roger has saved my bacon. So I have had diesel through the fuel and am surprised how dirty the oil became. It appears as though carbon deposits have been loosened and ended up in the oil tank. I haven't checked the oil filter as yet, but have changed oil and filter as recommended above albeit 7 years ago!
So question is, why does the diesel end up in the oil tank? I'm thinking it is because the cylinders are coated with unburnt diesel which goes around past the oil rings and then is scrapped off the side walls of cylinder into the crankcase then the oil tank. Is the appearance of the carbon in the oil tank a happy consequence as the engine is de-coked to a degree? I'm not recommending it as a yearly activity, more searching for a silver lining in a stupid error!
Thanks Roger and Mark!
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Re: Rotax 912UL oil overflowing. Why?
by Pasi Ilola » 4 years ago
Fuel goes into the oil because the choke stays on. Check it out. I have seen this once.
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