[Brucelee]

2.4 Dry Sump
PAG claims that the Boxster engine has an "integrated" dry sump, yet there is only one drain plug and no oil reservoir as on 911's. The instrument panel gauge and the dipstick read from the same source. There is an oil pump in each of the camshaft housings for oil return. The biggest difference from the 993 dry sump is the sump is located within the engine block on the Boxster rather than beneath it as in the 993. The sump, by definition, is the bottom of the crankcase where the oil flows to and collects after being pumped over whatever surfaces it was intended to lubricate/cool. The 993, and every 911 before it, uses a scavenge pump to pull out the oil as it flows into the sump and pump it into a holding tank under the right rear fender on all but a couple of early model years. Hence the term "dry sump;" oil is not allowed to sit in the bottom of the crankcase and so the sump remains (conceptually) dry. The main oil pump takes oil from the bottom of this holding tank and pumps it back into the engine's system of oil passages. The advantage of this system is that it prevents oil starvation during hard cornering. With a conventional wet sump system, high cornering loads can cause the pool of oil sitting in the sump to slosh away from the oil pump feed tube. With the dry sump's large vertical storage tank, you'd have to turn the car upside down to keep oil away from the pickup point. In the Boxster and 996, the tank is integrated into the engine block below the crankcase.

There are two techniques for oil to get from the crankcase to the tank below it:

1.A hole in the wall between the crankcase and the tank lets gravity flow the oil from the sump to the tank. If that's the case, then this is really just a conventional wet sump arrangement with an extremely large and well designed sump. Baffles and walls are designed into the sump to prevent the oil from sloshing out during cornering and the high capacity should ensure that plenty of oil is always available at the pick up point.
2.A solid wall between the sump and the tank prevents oil from flowing between the two. A scavenge pump moves oil from the sump to the tank when the engine is operating.
Both techniques are used in the Boxster. There are two oil pumps that take oil from the cylinder heads to the main oil pump. This oil is fed into swirl pots to be centrifuged and defoamed. There are oil collection channels cast into the crankcase to return oil to the oil pump.