Hi all, I've noticed that the 94 S350 has been getting pretty bad mpg. I've been averaging 16. Now this is in the city with fairly aggressive driving if you can call it that. But still that seems like S500 mpg territory not diesel. The engine was rebuilt 20k miles ago and it currently has 80k miles.

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1985 500SEL 124k miles
2001 Honda Civic EX

First thing to check is for a busted injector overflow line. If broken, a considerable amount of the excess fuel delivered by the lift pump will go one the ground instead, and this can be more than half the fuel used!

You should notice fuel on the ground, or at least a strong diesel fuel odor under the hood. Normally, you won't smell diesel at all on that car.

I would also check for a broken injector line (they fail at the injector end, spraying fuel everywhere).

The return line to the tank can also leak with age, same symptoms except for location. Ditto for a bad pressure line from lift pump (on the side of the injection pump) to the fuel filter and from filter to feed side of the IP (in front).

From there, you will need to check for badly dragging brakes (most likely rears), very late injection timing, or slipping tranny. Late timing will give you lots of smoke, which would not be normal on that car.

Also check the odometer -- if it isn't correct, you may in fact have decent milage but are not recording it!

16 mpg is very low for a 350 -- I'd expect more like 26.

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!

26 in town aggressively driving? i dont think so. and if you think that you will get 16 driving that way with a s500 i dont think so either. 10 to 12 is more like it. i dont think 16 for aggressive city driving is too bad.

of course check the fuel lines as mentioned above, but really i am not convinced that your mileage is too bad.

i have a 90 350sdl. i have gotten 26 on the highway only once. usually more like 24, running mostly 75.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

If doing city driving or lots of idling and sitting in traffic it'd be safe to assume that MOST of the fuel would end up on the ground....and a huge amount regardless.....if a return line blows, it'd be safe to say it would probably drain the whole tank within 20 mins with the engine running....the amount of fuel coming back out of the return hose is a good indicator....its at least a gallon a minute....so from a full tank I'd guess 15-20 mins. It would depend which line blew however, if it was one by cylinder 5 it'd probably be a much slower loss, but if it was one of the first couple it'd be spraying all over the place.....as you'd be getting the return from all the injectors instead of just one....

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I do smell some diesel under the hood after I turn the engine off. But there's no diesel dripping on the ground or anything like that.

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1985 500SEL 124k miles
2001 Honda Civic EX