I have the possibility of buying a 91 350sdl for 9k from a mercedes
dealership. They have all the books and records and have serviced it
from day 1. I am well aware of the problems with this engine from
my mechanic and info on mercedesshop.
Would it be insulting to have a compression test on this engine?
Would this tell me if the engine is faulty (i.e bent rods)?
I have owned a 85 300sd and 84 300d in the past


Thanks for input....

No.
Not necessarily. As I understand it, the only way to really really know for sure is to take the head off and measure.

__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

You probably will not be able to diagnose a bent connecting rod until significant damage has occurred to the block. The predominant indicator of a problem is excessive oil consumption.

So, can you get the dealership to warrant the level of oil consumption for the first 5K miles? Probably tell you to stuff it, but, if you state your concerns and you can get them to agree that it should burn less than 2.5 quarts of oil in 5K miles then you would be all set.

Unfortunately, I'm quite sure that they will believe that 1 quart per thousand is fine. This could already be well on its way into the "problem".

Without such a guarantee, you are rolling the dice to the tune of 6K.

tarom,

Not only is it not insulting to have a compression test done it is about your only real defense when buying any used car against the possibility of buying something with costly internal engine damage. A compressions test, if done in conjunction with a "wet" test and leak down tests, will detect cylinder wall damage and identify it as such. Any indication of a compression problem traceable to the cylider wall to piston ring condition is unsatisfactory. In fact, in my opinion any irregularities in the compression results are grounds to reconsider the deal. Always have a compression test done before buying a used car, from anyone. It is the only way to get past the external features of the car you like and see something about what kind of machine it is. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I think the 350sdl is the finest example of large mb diesels, with a good engine...

Mine now has a little over 100k and doesn't burn any oil between 4000 mile oil changes. The PO was extremely anal about this car, changed the oil every 2000 miles for the first 5 years. (he owned a diesel engine shop)

I guess that everything in life is a gamble, but if I got one of the good engines--after all only 900 of these sdls were imported in 1991. So, there are about 300 bad sdl's and 600 good sdls.

__________________
71 220D 169K wrecked
83 240D 118K sweet 4 speed
91 350SDL (one of the 60% good engines) 156K
84 300d (loaner to my sister) 189K
79 300SD (partswagen)
86 420SEL partswagen
70 220d (partswagen)
68 280s GASSER!!! under construction now
85 300sd 310K miles winter beater car retired
93 300d 2.5 turbo 168K wife's car
83 280SL euro 5 speed 155K
69 250S newest project 54K

If the rods are bent the pistons will be clanking in the cylinders and it will smoke -- this only takes a couple hundred miles at most to appear. Very nasty.

If it runs well, doesn't smoke, and has proper compression (get the compression test done!), buy it.

Nice car.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!