Maintenance FAQ for 7xx/9xx/90 Cars
Used Diesel. [Advice: Steve MacSween] A diesel with a blown head
gasket is a large, difficult-to-move paperweight. You cannot negotiate
on purchasing a diesel without a thorough inspection by a qualified diesel
mechanic. In most areas of North America (except possibly the midwest US)
as a general rule that means NOT a Volvo mechanic, from what I have heard.
They simply don't know enough about diesels. Go to a VW diesel specialist,
or find a heavy truck shop willing to work on diesel cars.
A thorough inspection must include at minimum
a compression test, and that is a bare minimum. You should ideally have
a cylinder leakdown test (CLT) done as well. Diesels run at around 20:1
compression -- compression loss means they become difficult or impossible
to start in cold weather. A compression test or CLT is pointless,
with the head gasket blown. If the head gasket is blown, there is
an excellent chance the head is warped and will need to be machined before
the new gasket is installed.
You will also need to have a mechanic assess
if the diesel injection pump is functioning properly. If it isn't, the
general cost to rebuild is in the area of $800-1500. Proceed
with caution when looking at a used diesel. Only buy a car with a favourable
(read: frequent oil changes), documented maintenance history available.
Diesel operating principles may seem (relatively speaking) simple. Repairing
them is neither simple, nor inexpensive.
Buying a Used 760T Diesel.
[Tips from Andre Lam] The problem with the I-6 D24 (and worse on the D24T)
is that the oil from the pump enters the head at one end of the engine,
and has to cascade down to the other end. This causes severe engine wear
during short runs. Ones the oil is hot and flowing freely, this becomes
pretty much a non-issue. If VW had re-designed the engine to put the oil
to both the front AND the rear of the engine then we might not have so
many unhappy previous Volvo diesel engine owners. Heck, I got better life
from the proven POS '81 Olds Delta 88 than either of the engines in my
'84 760TD. It seems that the VS and Audi engines were not as problematic
since they were 4 or 5 cylinders, and therefore the oil delivery was sufficient.
The other issue is the turbo charger in the 7x0 and 9x0 series diesels,
this further added stress to the engine. In their favor, the D24T was an
absolute dream to drive on the highway. The engine pulled strongly, and
was much more pleasant than a base B23 in a car that size and weight. Off
the line with the slush box things were a bit hairy at intersections. The
car seemed to wait a second or three for the turbo to spool, then pow...
the car started to pull briskly. This car had true turbo lag. Without the
turbo... its a dog, with the turbo... very brisk. Noise was very well subdued
as well. The engine ran very smoothly. I really liked the car (if only
the engine would last). If driven all day long, then the car will last
and last. If you drive it shorter distances, be prepared for an early engine
death experience. The cold start was an other item that needed to be checked
on regularly. If it was not functioning right, it could also contribute
significantly to an early death. The "wonderful" change over in Diesel
fuel a few years ago was also a real joy as upwards of %25 of all diesel
cars on the road had their pump die shortly after the cutover. Since the
pump IS the whole fuel system (pump and timing device) it is a complex
beast that costs about $700 to have overhauled, re-installed and adjusted.
They normally last about 100,000 miles, so that is not bad, but thanks
to the fuel, lots of people got "burned."
Would I purchase an other diesel car in
the USA. No way. For the last decade regular gas was CHEAPER than diesel,
and sometimes I could get premium fuel for less than diesel fuel.
Mileage was only so-so. My '84 760TD (w/ 4 speed automatic) got about 17
MPG around town and about 28 highway. I can easily beat that with either
my mom's 95 850 (4 speed automatic), and definitely better in my '93 850
(5 speed stick). Here in the USA it is also hard to find good diesel mechanics.
I took mine to the VW dealer hoping that at least they would have experience
ha! They declared the car in perfect health. Two weeks later my engine
is toast with below par compression. Rebuilds are possible, but here again
a good mechanic shop is hard to come by. In Europe where diesel is sort
of reasonably priced, gasoline is 4 times the USA cost, gas stations are
much more likely to also have diesel fuel, then my arguments can easily
be beaten with simple economics. The NEW direct injection diesel engines
from VW in the 850 are supposed to be really excellent. They run quieter
(not really a problem in the 7x0/9x0, but certainly so in the 2x0), don't
suffer from turbo lag, and get far superior mielage, and don't smoke up
the neighborhood when you take off.
Information Tips and FAQ. See the Volkswagen Diesel maintenance
FAQ site at http://www.bright.net/~vwdiesel/
for good information on the VW diesel (a variant of which is used in Volvos.)
Adjustments and Injectors. [Question:] How often do the valves need
to be adjusted on the D24? Should the injectors just be replaced at some
point or just run them until they fail? [Answer:] According to the book
you are supposed to check the valve clearance every 15k mi (25km.) Injectors
should go at least 75kmiles before nozzle rebuild. They don't usually fail
catastrophically. Usually you start getting smoke or excessive knocking.
adding a bottle of Techron to the tank will often clean out some of the
nozzle deposits and cut smoking and knock for a while. Bosch rebuilt injectors
are a relatively inexpensive swap.
D24 Diesel Valve Clearance Procedure.
[Query:] How do I set the valve clearance on the D24? [Response:
cool engine down completely.
1) rotate engine that 1st cylinder is
on T.D.C. (both cams are up 1st cyl. and mark on bellhouse aligned to flywheel
2) measure valve clearance for that cylinder
3) if too small obtain thinner plate and
exchange the old one with that one.
4) do it until clearance is 0.20 +- 0.05
mm cold for in and 0.40+-0.05mm for out valve.
5) rotate crankshaft for next firing cylinder
adjustment (1,5,3,6,2,4 order).
6) repeat procedure
7) rotate engine twice and check everything
8) do it every 20,000 km or so.
9) replace with new one valve cover gasket.
Be sure to point down plate side with number
on it. You will need pliers for valve plate and valve lifter tool.
It is the same tools and same procedure as for VW or any Audi diesel.
Rebuild. [Query:] I am looking for a source to either rebuild
my injectors or to purchase
rebuilt ones. Does anyone have a
source that offers good prices? [Response: Dimitar] I would suggest you
ask at a VW dealer or preferably Bosch. It is the same injector (or
nozzle for rebuild) as in VW Golf or any other VW/ Audi diesel car. For
D24 T opening pressure should be adjusted to 155 bar. Bosch part
no. of the nozzle is 0 sd 293.
Compression Test. [Query:] I am interested in getting a compression
guage to test the
compression. Unlike a gas engine
I'm quite sure that the guage would have to come with a fitting to thread
it into the injector holes since I doubt that you could hold it in place
with the high compression pressures of a diesel. [Response: Dimitar]
You are correct. For good engine performance it is rather important that
all 6 cylinders has close compression results, 6-8 bar difference between
When new compression is 33 bar and low
end (per manual and Volvo) is 24 bar.
Diesel Vacuum Pump Noise. [Query:] Anybody out there know how
to cure a knocking vacuum pump, it's like a noisy tappet but comes and
goes without any pattern. I have renewed the rod between the camshaft and
the pump without success. [Response:] We don't have 940 turbodiesels
in calif, but we used to overhaul the vacuum pump with a kit from volvo.
Occasionally, the big internal spring breaks, which can cause the noise
you're describing. you could try a new or rebuilt/junkyard pump from
somewhere, if you don't want to overhaul yours. keep in mind that
VW built that engine originally, and a pump may be available through a
VW parts outlet. [Response 2:] A new pump is around$550 and an overhaul
kit comes to $350. Also finding one in a junkyard is nigh impossible.
VW outlets have similar prices.
Oil Pump Gasket Replacement.
[Tips from Dimitar Vlahov] I will try to give a list of neccessary
work to change oil pump gasket on VW/Volvo diesel so that can be compared
with gas cousin.
First remove: valve cover, electric harness
big connector on firewall, front timing belt cover, front timing belt,
rear timing belt, injection pump turn away in bracket, PS pump, A/C compressor
and complete cooler and fan system. Anti freeze must be poured down
as to change front timing belt it is neccessary to move (and open) water
pump- water pump tensions timing belt-. Then, left and right engine
mounts are going off in order to pull engine out of bay for about 20-30
cm up. That is needed because to reach oil pump pipe bolts oil sump must
be off (and that is not possible with engine in place). Then alternator
and fan goes out, together with crankcase dumper which is 2 piece part
(and 400Nm or around 350lbs-ft torqued). When engine is almost bare
enough only then you can first unbolt carefully oil sump follwed by oil
feeding pipe inside. Only after all of that oil pump can be taken from
crankshaft and crankcase, remove paper gasket and inspect everything.
In process it is necessary to use some
special tools and it is GOOD to have factory green manual at least.
Assembly is obvious following the manual
(it is easy to say but not so easy to not forget some part or assembly
After everything is back on then you must
do proper engine timing of front and rear timing belts, injection pump,
cold start device. There is no marks on crankcase or crank dampener but
there is alignment point on flywheel. Also there is no any marks on timing
belts. When doing timing belts there also must be redone initial injection
I think that on D24 it is very complicated
to work for everyone who is accustomed to the Bxxx series Volvo engine.
It is completely different way of thinking from bottom to top of engine.
And prices for engine work seem to be higher then for any other diesel
engine around here. And yes, you can drive gas Volvo with slight
engine defect but diesel Volvo will not forgive any lack of precise and
in time service procedure. It is fragile to bolt overtension in alu head,
to head gasket at full temperature in summer, to cold winter starting,
to oil supply system, to cold start device. But if everything is
in original specification it has almost flat torque and is vibration free.
It is only 82 hp but still you can pull trailer with 1.500kg (3.300 lbs)
[Parts Source Tip from Kevin Rhodes ] Try the VW suppliers - Rapid Parts
and Wolfsports are two good ones - it's just a VW 4 with two more cylinders.
Used in VW trucks in Europe. Most parts are interchangable - there are
just more of them. The specs are pretty much the same too. My roommate
had a 740TD, always bought from Rapid Parts for FAR less than the Volvo
FAQ for 7xx/9xx/90 Cars
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