740 TurboDiesel - oil leak on high pressure side of turbo

Hi,

I have just bought a 740 turbo diesel from a garage.

A couple of days later I opened the bonnet and the whole turbo side of the
engine bay was black with oil.

I established that oil was leaking from the join where the metal pipe on
the high pressure side of the turbo goes into the metal box at the top of
the engine.

I took it back, and they changed some seals and said that they had checked
and everything else was fine.

A few days later and the leak is starting to come back; not nearly as bad
as before but no doubt it will get worse.

So there are a couple of issues:

(1) If oil is leaking from the tube I must be losing at least a little
boost pressure as well. However this may not be significant.

(2) Where is this oil coming from? The turbo has oil leads in and out ( to
cool the turbo) and I think there is also a scavenger pipe which comes
from the rocker cover area to feed any oil fumes back through the engine
(as with most petrol cars as well).
If there is enough oil in the inlet area to blow out under pressure then
this must be coming from somewhere, and also the rest must be going
through the inlet, the engine, and the exhaust.
It is almost as if oil is collecting in the bottom of the box on top of
the engine (presumably a reservoir for high pressure air by the inlet)
then being forced out of the join.
To coat the engine bay there must be quite a bit of oil leaking out, which
suggests that even more may be going through the engine.
Conversely it may (as above) just be collecting in the bottom of the box,
which could mean a lot less oil being lost.

I know that remote diagnosis is always difficult, but does this sound like
a worn out turbo which will never be cured, or did they just not do a very
good job when they changed the seals?

They also told me they had to wait a while for some silicone sealant to
cure before road testing the car.
Does this sound like a reasonable thing to be doing, or is silicone
sealant a 'bodge'?

TIA
Dave R

 

It's been a while since I've seen under the hood of one of these, are you
saying the oil is leaking from the pipe that connects the boosted air into
the intake manifold? If that's the case there shouldn't be a significant
amount of oil there to begin with unless the seals within the turbo itself
are shot. First thing I'd try is to scrub the engine real well so you can
see what's going on, then assuming it's an automatic (every 760TD I've seen
was anyway) have someone plant their foot firmly on the brake, put it in
drive, and press the accelerator enough to create some boost while you stand
to the *side* watching under the hood for leakage. Don't do this for very
long without allowing the transmission fluid to cool but a short period of
time won't hurt anything.

 

(1) Yes, I am sure. It is the vertical pipe that goes up from the turbo to
the intake manifold. The leak is at the top of this pipe, where it goes
into the manifold (or at least the box before the manifold).

(2) No it is not automatic; in the UK there are quite a few 740s with
manual gearboxes.

(3) I have already cleaned it off and test driven it; that is how I know
where the oil is coming from.

(4) The garage did the same clean, drive, check and confirmed where the
oil was coming from before they tried to fix it.

(5) You have actually answered my main question with "there shouldn't be a
significant amount of oil there to begin with unless the seals within the
turbo itself are shot".

So; new questions.

Is there anything apart from having 'shot' seals in the turbo which would
put oil into the intake?

Are shot seals easy to fix (the garage would be doing the fixing) or is
this a sign of general wear in the turbo which means a new (or newer)
turbo?

They claim to have changed some seals already; which seals would these be
if not in the turbo?

TIA
Dave R

 

You need to make sure that there is no oil in the air intake filter box. If
that is OK and dry then make sure that the airway to the compressor is fine
with no oil contamination. Then remove the tube to the inlet manifold (the
long square cross-section box is a plenum chamber to even out the air flow
to each cylinder. It is possible that your 740TD may have Exhaust Gas
Recirculation fitted. If it has, the plenum chamber has probably become
clogged with carbon/oil mix. If possible get rid of the EGR gear. Ensure
that the plenum chamber is free of contamination. Do a compression check on
all cylinders and check injectors for leaking seals. Check glowplugs and
relay for correct operation and that the thermostat is working how it
should. Too cool a diesel engine gives coking up which can contaminate the
airways and reduce performance. Was the garage a Volvo dealer or just a run
of the mill garage? If they get stumped then take your car to a VW/Audi
commercial dealer whose mechanics should be well capable of restoring your
engine's good manners and general cleanliness. With these earlier diesels
the tappetts must be checked/adjusted every 20,000 miles, cambelt and pump
drive belt changed every 80,000 miles and take care when adjusting the
cambelt tension. The adjustment is carried out using the water pump as a
tensioner so most people change the water pump and gasket when changing the
cambelt to avoid coolant leaks. Your engine should be pushing out 109 bhp. A
great improvement can be had by retrofitting it with the intercooler from
the 760 GLE Turbodiesel (needs different inlet manifold, turning the turbo
outlet through 180 degrees, and fitting extra air hosing and different
brackets for the alternator). This is what a friend has done and has gained
a bhp increase to 122 bhp. They can be reliably tuned to produce 180 plus
bhp with a corresponding increase in torque. Whilst one of the causes could
be what James suggests it is not the first thing to plump for. The best way
to sort out turbos is first to determine if there is too much play on the
compressor end of the shaft. If you find too much then a core replacement is
cheaper than a complete turbo and sorts out the seal problem at the same
time (Turbotechnics are the guys to ask).

Best of luck and please keep us informed of your progress. There are quite a
few diesel nuts who like these quite impressive cars and can be found on the
Volvo Owners Club Forums. (http://www.volvoclub.org.uk)

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

I don't know how this applies to TDs, but in the "fuel" version crankcase
pressure is a culprit in forcing oil out of the turbo. The oil (in the
gassers) normally is not under any real pressure as it is introduced into
the turbo and the crankcase pressure is a significant force to cause oil to
spill into the chambers. My 230ft smoked badly at idle not long ago but not
at cruise. When I got the entire crankcase ventilation system clean it
stopped (whew!)

As I say, I have no experience with Volvo TDs. The only commercial TDs I've
been near (one tour boat, one bus) lost extraordinary amounts of oil -
several gallons per hour - when they apparently had seal failure.

Mike

 

I had a 'phew' moment with my 2.3l petrol 760 Turbo (previous Volvo) when
the breather pipe from the rocker cover (?) to the air cleaner box became
blocked - the wire filter thingie at the end was really gunged up!

The car suddenly started laying down a trail of blue smoke.

I thought the turbo was on the way out.

Once the Volvo dealers cleaned it all up it was fine - a lesson in going to
non-Volvo garages who are not familiar with all the servicing requirements.

I was hoping this would all be checked because the people who sold me the
car are Volvo specialists and enthusiasts - although not a Volvo dealership.

To recap:

car bought
leak discovered (Yike! - oil everywhere in the engine compartment on the
driver's (turbo) side)
car returned to vendors for repair.
fixed with 'new seals' and 'silicone sealant' (reported)
soon after, leaking again

I am now about to return the vehicle for the second time, but need to know
what the implications of this oil leak are.

If the turbo is completely knackered then it is new turbo or return the
vehicle as 'not of merchantable quality'.

If it is a minor thing they didn't fix properly then they can get it right
this time

I am in a quandry; the leak is nearly cured (I will clean it up tomorrow and
see how much it leaks now) but there still seems to be some leakage. Do I
return the vehicle while I still can, or is this a minor teething trouble at
the start of a good relationship?

As an aside, the oil scavenging seems to be very simple - there is a plastic
'hat' on top of the rocker cover and a rubber tube leading down to the inlet
just before the turbo. Far simpler than the 760 turbo. If the problem is
crank case pressure where (apart from valve stem oil seals or knackered
rings) is this likely to come from?

TIA

Dave R

 

Some diesels develop a leaky head gasket through not having had the head
bolts retightened 1,000 miles after a head removal. This problem went away
after 1993 due to redesign of parts of the engine and a different head
gasket type which did not require the head bolts to be retightened 1,000
miles after head replacement work. Inlet manifold gasket(s) can also cause
leaks of oil when they are loose.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

I would say the most likely cause is oil being blown in through the PCV
system. Disconnect the PCV hose between the air filter and turbo. Plug
the inlet to the air intake, and see what blows out the PCV hose. This
could indicate as cheap as a general PCV system cleaning or as expensive
as an engine rebuild if there's simply too much blow by.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Just a brief update (I enclose the original posting because some
newsreaders will have dumped the thread by now).

The fault is still not cured despite yet another attempt by the garage to
fix it; this seemed to be even more silicone.

There is also now a major electrical fault which drains the battery but
doesn't show any warning lights.

I can tell you it is very spooky watching your on-board electrical
systems shutting down one by one for no apparent reason.

Picture the scene - rainy day on the dual carriageway, cruising around 70
mph.

The windscreen wipers seem to be getting slower.
I notice that the speedometer is now reading around 50 mph but I am sure
(rev counter and relative speed of the other traffic, engine note etc.)
that I am still doing around 70.
I come out of overdrive as I merge down a ramp onto the motorway.
Overdrive will not re-engage.
Suddenly the radio cuts out.
Wipers still working, a quick check and the electric window seems to move.
Speedometer still reading low, although the rev counter seems fine. The
fuel gauge starts to move towards zero.
I notice the running lights seem to have gone out; I can't see the glow
from the high level brake light when I brake.
Turn indicators stop working.
Soon I am left with just the rev. counter and the temperature gauge.
Thankfully it has stopped raining, but before I can get to a sensible
intermediate point the rev. counter starts to drop away, then the engine
stops.
RAC come out, but can't get the car to jump start; can't even get it to
start using their battery with mine disconnected.
Conclusion; major electrical fault to earth.
Some kind of earth fault near the battery.
I was betting new alternator.

One thing to note - in the absence of a speedometer a GPS seems to be an
acceptable substitute.

Bad news - garage hasn't managed to fix the electrical fault and the car
is now immobile again (fortunately on my drive this time). The oil leak is
also not fixed.

Time to invoke the Sale of Goods act and reject the car as not suitable.
Sad, because if it was working it would be exactly what I wanted.

Cheers
Dave R

 

That's too bad...

An electrical fault that severe should be very easy to track down
though, my first suspect would be one of the battery cables or the
ground strap to the engine.