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SBK930 SBK930 is offline
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Join Date: Jul 2016
Location: Australia / Straya
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Quote:
Originally Posted by Jim2 View Post
Too light of oil weight could flow excess through turbo then overwhelm gears in scavenge pump. 15-50 is fine.

Old used oil goes thin, causes same issue I mention above.

Idle speed, remember scavenge pump is run from a cam, therefore half crank speed. If idle is too slow yet idle oil pressure is high when oil is warm and thin, scavenge pump can be overwhelmed. 800 idle rpm increased to 1000 rpm is a 25% increase, with an equivalent increase in scavenge pumping capacity.

Alan, turbo seals are by no means positive. They rely 100% on gravity to drain oil, along with a bit of slinger affect. 2 psi crank case pressure would probable be an issue. In fact my 993 had about half the breather vent area of a 930, pushed oil out both compressor and turbine ring seals until I improved the crankcase ventilation to match that of a 930.

I'm no expert, just throwing out ideas in order try and narrow the issue down.
Hi Jim,
Thanks,
Crank case oil pressure is around 40 psi at cold start, and then when at operating temp is around 15 psi. This is at idle. The turbo has run at these pressures fine for years. The oil that runs through the turbo is efficiently being circulated by the scavenge pump, as the pump more than keeps up with the oil flow when cold and keeps pace when oil is hot but is more efficient under load when hot. I still have the original drip tank that is vented to the air cleaner box. Which is leaving me struggling to understand where the excessive pressure could come from to force oil past the rings.
This turbo has got to be ...............well POO!
Old 06-04-2017, 09:14 PM
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