My 300SD has just over 300,000 miles on it...I've owned it for 1 year, and its been running great; however, recently, I cant get over 55 mph on uphill interstate driving...engine runs great around town and side streets but seems to be starved for fuel at highway speeds. The transmission shifts fine (but a liitle hard) through all the gears. I am guessing it needs both fuel filters changed, but i read the procedure in the manual, and was a little hesitant to change the filters because it says something about "manually pumping" to bleed the lines. Do my symptoms point to a fuel filter problem, and if so, is this an easy job?

Sounds very much like clogged filters. Change them, unscrew the little white primer pump, pump it a few dozen times, screw it back down, and crank till it starts. Easy.

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Yes, your SD's symptoms match exactly what my '83 300SD would do when it needed a new main fuel filter.

The bleeding is easy. Unscrew the white colored knob after changing the filter, and pump it until it stops, then screw it back in.

*NOTE:
BACKFILL THE FUEL FILTER WITH DIESEL FUEL, WHEN REPLACING.

thanks for the info...sounds easy...haven't seen a white colored lever, where is it?

Never had to bother with priming the system after changing large secondary filter myself. Load the cannister with diesel fuel - then engine oughta prime itself.

And if your repair manual says you MUST pump prime the system but mentions nothing of pre-loading the filter with diesel fuel - then discard the book as providing bad advice. Many of us here wonder why MB bothered with manual priming pumps at all, understanding it makes more sense to open an injector line instead.

The primer pump handle, "white colored lever", is located between the IP and drivers fender, follow the fuel line. It needs to be unscrewed and pumped, screwed back in when done.

Yes DD, filling up the secondary filter with fuel will result in not having to prime, that's what I do. I imagine MB installed it for if you were to run completely out of fuel, for whatever reason, and did not have access to fuel to fill up the filter. Less wear on your starter and battery also.

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83 SD

84 CD

DO NOT use fuel out of the old filter to fill the new one. Discard the old filter and everything in it.

I always thought the pump was pretty handy.

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.