3.0 TURBO OIL DRAIN BACK QUERY.

[1975turbo]

My '75 turbo has developed the rather un-nerving tendency to smoke excessively on start-up and continue to do so until 15 miles or so and then it is fine. I think intermittent use is not helping. The car had a good run 4 days ago and I checked the tank today and it is not registering anything on the dipstick (it measured 3/4 full on the dipstick after the run 4 days ago). Is it normal for the tank to drain all its contents into the sump after such a short time? I would think the engine would manage to re-fill the tank pretty quickly after start-up, so I'm puzzled at the distance needed before it runs correctly without bellowing out smoke.

I know you shouldn't fill the oil tank to the top of the dipstick, but is even 3/4 full too much and causing the problem? Is there a valve in the system that is faulty and allowing such a fast drain into the sump?

Any thoughts / opinions welcome.
Thanks,
Chris.

 

[JamesCookson]

Hi Chris - good to hear from you - I trust you are well.

My 930 (1975) had exactly the same problem - lots of white smoke on first start up, that went away once the engine was up to temperature. It was diagnosed as oil getting over the turbo seals and pushing out into the exhaust side of the system, this then vaporized to produce embarrassing volumes of white smoke.

The issue was cold oil not draining from the catch tank under the turbo, which was caused by wear on the scavenge pump running off the front of the left hand cam. The worn scavenge pump was unable to pump against the much larger oil pump from the engine so oil from the turbo was not being drained back into the system, result it flowed out through the point of lowest resistance - the turbo seals on the cold engine.

I changed the scavenge pump and the problem was solved - but be careful - Porsche UK provided a replacement scavenge pump but the seating length was slightly longer than original, as a result once up to temperature it expanded and seized solid with the cam - fortunately sorted by Porsche under warranty, but please do check the shaft length against the 1975 pump - the difference was probably less than 2mm and not easily visible.

Once changed I had no more issues with white smoke on start up

Good luck - great to hear you've still got the 930

James

 

[1975turbo]

Hi James, great to hear from you too!
Many thanks indeed for that wonderful explanation of the problem and the solution, together with the warning on the replacement part. I had a similar problem with fuel pumps, where (expensive) replacements failed. In the end Porsche had the pumps re-engineered and were able to supply one that is fine (fingers still crossed though!).
Do you still have your 3.0? If not what did you replace it with?
Kind regards,
Chris.
Tel:01432 371775
ps that's twice you have "saved my bacon" - I think I owe you a pint!