Turbo Oil "tank"...what was Porsche thinking?

[Tilikum Turbo]

With the whole oil system capacity roughly 12-14 quarts, what was Porsche thinking when they placed a very small oil reservoir(with allen head to drain) that only has roughly a half-cup capacity of oil.

Porsche engineers typically do not design or implement superfluous mechanical items on the cars/engines, and I was wondering if this small amount of oil is actually a 'slag' that results from the turbo operation itself? Just curious if anyone else knows some details or history about this.

Thanks!

[RarlyL8]

The turbo drip tank is part of a circulation sub-system. Look behind the passenger's side rear wheel and you'll find the rest of your oil.

[Tilikum Turbo]

Originally Posted by RarlyL8

The turbo drip tank is part of a circulation sub-system. Look behind the passenger's side rear wheel and you'll find the rest of your oil.

I know the lines that are forward of the thermostat leading to the oil cooler up front and back don't get drained with a normal oil change, so why intergrate this tiny drain system to bleed off what would be maybe 1-2% capacity of oil, when 10-12% is left in those lines running back and forth up front?

In other words, is this critical to drain this along with the dry-sump tank and engine, since it amounts to so little oil in the big-picture?

[Noah930]

For clarification, you're asking: while already draining the oil tank and crank case during an oil change, is it worthwhile to also drain the little catch tank?

I don't.

[mppickett]

Originally Posted by Tilikum Turbo

I know the lines that are forward of the thermostat leading to the oil cooler up front and back don't get drained with a normal oil change, so why intergrate this tiny drain system to bleed off what would be maybe 1-2% capacity of oil, when 10-12% is left in those lines running back and forth up front?

In other words, is this critical to drain this along with the dry-sump tank and engine, since it amounts to so little oil in the big-picture?

No. You do not usually drain the turbo drain tank. Actually, if you hold the throttle around 2000 rpm for 15-20 seconds before you turn off the engine, the turbo drain pump (attached to the back of the left bank camshaft) should mostly drain the turbo drain tank for you and pump it into the large oil tank beside the rear passenger wheel mentioned by Rarlyl8. This usually eliminates the characteristic puff of blue smoke on start up (if you hold your mouth just right).

[JFairman]

Originally Posted by mppickett

No. You do not usually drain the turbo drain tank. Actually, if you hold the throttle around 2000 rpm for 15-20 seconds before you turn off the engine, the turbo drain pump (attached to the back of the left bank camshaft) should mostly drain the turbo drain tank for you and pump it into the large oil tank beside the rear passenger wheel mentioned by Rarlyl8. This usually eliminates the characteristic puff of blue smoke on start up (if you hold your mouth just right).

When I worked at a german car street shop it was normal procedure to drain the factory turbo sump tank along with the main oil tank and engine case.

We would also disconnect one end of the large S hose at the bottom of the oil tank and let it drain out and also the oil line coming back to the tank from the external thermostat.
It takes a little extra time to do that but it gets more dirty used oil out and thats a good thing.
Porsche oil changes took longer so the labor charge was higher than most other cars anyway.

[RarlyL8]

I always drain the turbo sump tank into a sepparate container for inspection. That is a potential problem area when it comes to contaminated the oil. If your turbo is failing or coking you may see signs of it on the sump tank plug in the form of sludge or particles.

[175mph951]

if you question was why is this there, then the answer is because of the amount of oil fed to the turbo. it helps to empty the turbo faster..the oil comes into the turbo at high pressure and volume. 60-80+ psi. if only had a drain line running out of the turbo to the scavange pump, it wouldnt drain fast enough. the oil would build up in the turbocharger and it would either leak past or completely blow out the internal seals resulting in smoke from the exhaust. it basically just stores the oil until the scavange pump can pump it away without letting it get backed up. this is different then most other cars in that the turbo is usually higher then the crankcase and returns directly in to the oil pan as in a 944t. on the 944t you can notice how much bigger the oil reurn line is then the oil feed. i also agree with what was said before this should be drained with a normal oil change.