940 SE Turbo - oil consumption

Mine does use oil too at about 2 litres every 6000, so needs topping up half way through service interval.

I have several non Turbo B2xx engines before and inlet valve stem leakage is rare. I did do the head on my highest miler (200K miles) minor leakage at around 150K, but I did push the car hard. In comparison the Turbo drinks oil. If you think about it Turbos suck less on the seals so it should be less of a problem with air being pushed in.

The most obvious sign of inlet valve leakage is blue smoke on start up.

I think Turbo oil usage is quite common, by the sounds of it yours needs doing, mine probably not far behind.

-- Tony Stanley ++Always Learning++

Many thanks for most helpfull comments.

I should have said that tubo was replaced as a first option, but had no effect on oil consumption, however it was a second hand turbo so it could still be the cause. I still suspect the valve seals so will give it the test suggested.

Thanks

Regards Jeff

In article , snipped-for-privacy@virgin.net by Edward Milan dropped his wrench, scratched his head and mumbled,

Most turbo oil consumption is from crankcase pressure pushing oil up out of the oil separator and into the manifold. Once in the engine it is burned then the smoke cleaned by the convertor until the catalyst is coated. Make sure the PCV system is working correctly.

Bob

Been thinking about this for while now, but I can't understand the mechanism. Why should crank case pressure push oil out of the flame trap/oil seperator.

On my car crankcase pressure is sucked into vacuum by a connection to the Turbo inlet side, as otherwise the connections would have to be pressure sealed. There does seem to be some terminaled device at the inconnect point which I don't know the purpose. There is also a diaphram device connected to the exhaust and inlet manifold (by metal pipes), and driven by a vacuum line with another electrical device in the air circuit to the manifold (ie it could be a pressure switch or sensor which controls this EGR thing). Haynes manual seems to be no help atall.

All the pipes were oily but not dripping.

I'm familar with non-turbo simple cankcase ventilation on UK B200s (No EGR), but havn't grasped this turbo thing yet. What things go wrong with it, how is it likely to cause oil consumption? The non turbo just blocks up and blows out seals coating the engine bay with oil, or in some circumstance the small nipples block causing mixture problems as the air bypasses carbs and things.

-- Tony Stanley ++Always Learning++

Oil vapour and fine liquid droplets get into the air in the crankcase, mostly through agitation by the moving parts. Extra "air" gets into the crankcase from blowby, and of course the higher the cylinder pressure, the more extra "air". This extra "air" has to leave through the PCV system, so more "air" then moves faster through the oil trap, giving it less time to remove the oil. If the system is not clean, then it doesn't work as designed, and the crankcase pressure goes up, and less oil is condensed out. This extra pressure also inhibits oil return from the turbo drain pipe, allowing extra consumption through the turbo bearing. And of course the extra pressure can get relieved through oil seals, in the mechanism you're familiar with.

To minimize oil consumption, keep the PCV clean. You may have to put in a new oil separator if the old one is too gummed up, because of the labyrinth design it's pretty hard to clean. However, it's not uncommon for those motors to use a bit of oil even when the PCV is in perfect shape, but this will minimize it.