Engine: Diesel                                                                                                 FAQ Home

 Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0
Purchasing Used Diesel

Diesel Information Tips and FAQ

Valve Adjustments and Injectors

Injector Rebuild

Diesel Compression Test

Turbo Diesel Vacuum Pump Noise

Diesel Parts

Purchasing 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.

Diesel 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.)

Valve 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: Dimitar]
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 mark)
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 again
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.

Injector 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.

Diesel 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 any two.
When new compression is 33 bar and low end (per manual and Volvo) is 24 bar.

Turbo 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 timing).
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 pump timing.
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) effortlessly.

Diesel Parts.   [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 dealer.

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