Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

pressure regulator that sticks shut with pressure on the vacuum line from the intake manifold,
increasing the pressure to the injectors to full pump pressure, which is near 100 psi. To
determine if the pressure regulator is malfunctioning, monitor fuel pressure under boost.
[Another Response:] Check the hoses and fittings to and around the turbo to be sure none are
loose or have leaks, including the turbo compressor inlet hose. This can cause poor
acceleration or running rich. The breather box on the intake side of the engine which is hard to
get at, if clogged can cause the turbo to blow oil through its seals. If the turbo has lots of miles
on it you may have a bad turbo which is blowing oil also. Don't drive with the turbo blowing oil as
it will clog the cat converter! When the engine is cold you can take the rubber hose off the intake
side of the turbo and see if the shaft has excessive play, or is frozen.
Turbo Blows Smoke: Overfill Oil. I have received several messages from Volvo neophytes
relating the same or similar stories: "I went to the quickie lube, where they proceeded to overfill
my Turbo-engine oil by [1-2-3] quarts. Just after I started up and drove out, thick clouds of blue/
black smoke came out the tailpipe. Now my mechanic says I need a new turbo. What gives?"
I am not exactly sure how to diagnose this, but let me throw out a couple of hypotheses for
comment:
1. It would appear that anything restricting the turbo oil drain would cause the unit to overfill and
blow oil into the exhaust pipe. If the car were seriously overfilled with oil, this may have an effect
on crankcase ventilation, probably starting at the oil breather box drain. So overfilling might clog
the breather box, interfere with crankcase ventilation, stop the oil drainage from the turbo, cause
the turbo to overfill, and allow this extra oil to be forced out past the turbo seals.
2. Similar hypothesis but the unrelieved blowby increases the oil pumped to the turbo and not
drained, causing excess oil in the turbo, increasing crankcase pressure, and forcing this oil out
the exhaust.
If either of these are correct, then fixing the problem merely means draining the oil, replacing
with the correct amount, and cleaning the crankcase breather system. Oil burning should then
stop at once. Why would the turbo unit be damaged? If indeed it was damaged at all (another
dealer boat payment due?) Thoughts?
[Response: Abe Crombie] The seals used in turbos are a single piston ring type seal and a
labytrinth seal system. The labyrinth deal is simply slinger washers in a cavity through which the
oil would have to travel against centrifugal force to leak out. If you overfill engine the oil is
restricted in draining back to the hole in side of block because the hole is now covered by oil
being splashed up into the drain tube. With no easy path to drain the oil out of the piston ring
seal area the oil can be passed through both the intake housing seal and the exhaust housing
seal. The flame trap/crankcase breather system being plugged has similar results. [Response:
Jim Stephenson] I believe this is the answer. My turbo was overfilled and would blow clouds of
smoke. The oil was being burped up through the breather box and would run in to the turbo.
Under heavy boost it would drag the turbo impeller down and shortly after that a BIG cloud of
white smoke would billow out the back. After I changed the oil no more problems. But what a
mess!!! [Response: Rob Bareiss] This experience shouldn't result in a damaged turbo.
Mechanical parts don't usually fail due to TOO MUCH oil... The turbo might not pump oil very
efficiently, and it could conceivably do something strange if a lot of oil hit the vanes as it was
spinning at a high speed, but they're pretty tough little units. I could see damage to a catalytic
converter resulting from this. [Contrary Opinion: John O] I've rebuilt my original turbo using IPD's