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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,274
There are 2 seperate oil circuts in a 911 motor, and a third small one for the turbo sump in a 930.

The main oil pump in the crankcase is actually 2 seperate pumps together, a scavange pump and the main oil pressure pump.

Starting with the scavange pump oil in the crankcase, all the oil in the crankcase is pumped out of the engine to the external oil thermostat next to the torsion bar cover in the right rear fender well.
This pump is not high pressure because it is not pumping oil through small oil clearances in shell bearings so there is not much restriction to flow but it moves alot of oil.

If the oil is cold or just warm it is diverted from the external thermostat back to the oil tank where it is pushed through the spin on oil filter and then it settles into the baffled oil tank.

If the oil is hot like up around 170 degrees, (I don't know the exact opening temperature) then the external thermostat diverts the oil forward to the external oil cooler in the right front wheel well. From there the oil flows back through the oil line to the external thermostat and on to the oil tank where it goes through the oil filter and then settles into the oil tank.
Thats the scavange oil circut.

The other half of the crankcase oil pump is the main pressure pump.
It sucks oil from the bottom of the oil tank through the large S shaped hose into the engine's oil pump.
From there the pressurized oil goes to an internal thermostat in the top of the engine case next to the oil pressure switch and crankcase breather.

If the oil is cold or just warm that thermostat diverts the oil around the engine mounted oil cooler and sends it to the oil galley where it branches off to the crankshaft main bearings and on to the rod bearings and at the end of the oil galley it branches off to the cam towers through external oil lines to lube and cool the cams, rocker arms, and valve guides.

If the oil is hot the internal thermostat in the engine diverts the oil through the engine mounted oil cooler and after that it goes to the oil galley, etc.

On a 930 there is one more small external oil pump on the end of the driver side camshaft that sucks oil from the turbo sump and pumps it directly to the oil tank unfiltered.

hope that helps...
Old 11-15-2009, 10:46 AM
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