940 SE Turbo - oil consumption

Hello

10 year old - 157000 miles - goes like a bomb but using oil at 5 ltrs
per 6000miles.(semi synthetic) Smoke from exhaust when under heavy
acceleration in 3rd.

No evidence of leaks, is it possible the valve stem seals are shot?
and is there any way to check? I cannot think that it is the bores,
performance is too good,

Any suggestions would be most appreciated.

Regards Jeff

 

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.

940 SE Turbo 2.3L, 1995, 110,000miles

 

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

 

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.

 

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.