It has been suggested that the oil in my turbos could be caused by blowby.

I am assuming blowby is escaping gas from the combustion process, into the sump? If so, then does this affect the oil return from the turbos, and in worse case scenario, push the oil through the turbo oil seals?

Apologies if they sound like naive questions, but I have good even compression on all faces (~7 bar), so would there be enough blowby gas to actually cause enough pressure build up to cause the oil to back out of the turbos?

In addition, I have run the car without the oil filler neck cap in place - I am making the assumption that any pressure in the sump would then be releaved - I am guessing the sump is not sealed off from the oil filler neck?

Cheers!

 

an easy way to check for this:

hold a piece of paper behind your exhaust gasses. if the paper flaps evenly going away from your exhaust, then you are good. if the paper flaps towards your exhaust at any point (IE: being sucked in), then you have blowby and you need a rebuild.

 

There is a return line from the oil filler neck which routes the blowby gas to the turbo intake. The purpose is emission control, to cause such gas to be burned in the engine.

Under sustained high lateral accelerations, oil - rather than just blowby gas - can enter such return line and foul everything, turbos, IC, solenoid valves, and instrument sensor along the path to the intake.

If you insist on driving your turns hard... you should install an oil catch can.

Also, never overfill when changing oil and keep the oil level preferably on the low side.

You can find more information on how and why at http://www.fd3s.net/oil.html in the Oil Catch Can section.

- Sandro

 

Thanks for the reply. I have actually looked at this and put a catch tank into this line. Absolutely dry. So 100% sure no oil is getting to the turbo pack via this route.

 

Interesting - and this really works? (Why would it suck the paper towards the exhaust? Presumably you don't mean sucked towards the exhaust, just that there is less gas expelled since some of it lost via blowby and so the paper will flap unevenly?)

 

from the intake stroke of the rotor and a bad seal, it would suck in from the exhaust and intake.

 

In my experience and from what I'm told, that test is a myth.

Also, I don't have a very good oil flow diagram, but it doesn't seem possible for combustion gasses to pressurize the turbo oil system.

 

what kind of nonsense is that!?!?

 

Just like so many things, no one seems to know definitively what is real or not. I have been told by several people of sump pressurisation and this affecting oil return from the turbos. That said, I'd have thought it would need to be a pretty high pressure to cause back up to the oil flow. And with ~7bar on all faces, I can't see I am loosing much combustion pressure anyway - but maybe I have that worng to!