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Old 10-02-2005, 02:21 PM   #1
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What does the oil separator do?

My wife and I had the pleasure of meeting Randall Neighbor today and having lunch with him and the question came up. I told Randall our Boxster has been relatively trouble free except for the recent ignition switch, coolant reservoir and oil separator. He asked "what does the oil separator do?" to which I said "I have no idea, but it took care of the smoking problem I had."

Sooooo.....what exactly does it do?

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Old 10-02-2005, 02:34 PM   #2
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Oil flow that's free of cavitation is critical to a high performance engine. This cavitation process happens when oil splahes against moving parts, like crankshaft, bearings and others. The Boxster engine uses a dedicated oil scavange pump to extract oil from each bank of cylinders, then sends it to a defoaming chamber before sending it back to the oil sump.

From there, the oil is pumped to the lubrication points, and the cycle begins again.

This also ensures consistent lubrication, even in more extreme high speed corners.
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Old 10-02-2005, 02:38 PM   #3
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Thanks bmussatti!

Do you know if this this helps with "dry sump" condition I've read about?
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Old 10-02-2005, 06:25 PM   #4
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Quote:
Originally Posted by deliriousga
Thanks bmussatti!

Do you know if this this helps with "dry sump" condition I've read about?
John,

There is no thing as a Dry Sump condition. Perhaps you're confusing Dry Sump with Oil Starvation.

Most cars have a Wet Sump Oiling System. In a Wet Sump Engine, the oil that you put into the engine is stored beneath the crankshaft in the oil pan. Because of the volume of Oil it must contain, it's fairly large and bulky. A single Oil Pump sucks oil from the bottom of the oil pan through the Pick-up tube, and then pumps it to the rest of the engine.

In a Dry Sump Engine, oil is stored in a Remote Tank outside the engine rather than in the Oil Pan. A Dry Sump System has at least two Oil Pumps. One pump pulls oil from the sump and sends it to the Remote Tank. Another pump sends Oil from the Remote Tank to lubricate the engine. With this arrangement, a minimum amount of oil remains in the engine.

Since a Dry Sump Engine does not have an Oil Pan, the Center of Mass of the Engine can be positioned lower in the vehicle. This helps lower the car's Center of Gravity, and allow better aerodynamics by accomodating a lower hoodline.

Also, there is no limit to the Oil capacity of a Dry Sump Engine - the Remote Tank can be as big as you want. And, this Remote Tank can be located anywhere on the car.

In a Wet Sump Engine, forces from Turning, Braking and Acceleration cause the Oil to pool on one side of the Oil Pan. This can cause Oil to raise over the Crankshaft and cause considerable power-robbing Drag, as much as 10-15 HP. Also, Oil can move away from the Pick-Up Tube, giving the Oil Pump nothing to pump for a few seconds. This causes a reduction to the Oil used for lubricating the parts and the Crankshaft or Big-End ConRod bearings can temoporarily cease to Float causing metal-to-metal contact. It takes very little time for this condition, at high RPMs to cause Engine Damage. This is known as Oil Starvation. Another cause of Oil Starvation, especially in V Engine configurations is that the Oil , again due to high Acceleration/Braking and Lateral Forces, can pool in the Head rather than return to the Oil Sump to be recirculated. When this happens, there can be an insufficient Oil Level in the Oil Pan for the Pick-Up Tube to reach and draw off again. Manufacturers and Aftermarket suppliers have introduced Baffling in the Oil Pan to help combat this problem. These baffles are essentially Sheet Metal Fences which block the Oil from sloshing around so much, but these are only so successful. Compromises must be made between blocking the migration of the Oil away from the Pick-Up Tube when driving to extremes, and allowing the Oil to drain back to the Pick-Up Tube in normal operation.

Dry Sump Systems do have some disadvantages. The system weighs more, and is more complex with additional plumbing to send and receive OIl to/from the Engine. Also, there is an additional pump, doubling the possibility of Pump failure.

But, in a high performance Engine, the advantages generally far outweigh the disadvantages. Some cars, like the Lotus Esprit were available with either a Dry or Wet Sump Engine. Hope this helps...

Happy Motoring!...Jim'99

Last edited by MNBoxster; 10-02-2005 at 08:12 PM.
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Old 10-02-2005, 06:45 PM   #5
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John, it sure was great to put a face with a screen name, and to drive your boxster! It really makes me feel better about my 2.5 when I had the chance to drive your 2.7... it felt a little stronger, a little smoother, but not terribly different.

Now I need to drive a 3.2!

I'm going to re-read this thread again when I'm not so wiped out from speaking and consulting all day today. I need to get my head around oil seperators and dry sumps on a fresh night's sleep!

Good reading material on the plane tomorrow...
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Old 10-02-2005, 07:45 PM   #6
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This is what bmussatti said.
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Old 10-02-2005, 08:43 PM   #7
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Quote:
Originally Posted by Tool Pants
This is what bmussatti said.

@ToolPants,

TP, your pic confirms what I have read in my Shop Manuals, namely that there are actually two (2) Air/Oil Separators, one for each bank of the Engine, which makes sense.

You always hear people refer to it in the singular indicating that there is just one.

I assume that when one refers to replacing the Air/Oil Separator, they actually mean swapping out both of them.

Happy Motoring!...Jim'99

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