300D Mileage

-->> T.G. Lambach sanely.

By those numbers I have no reason to complain; I average 26 in typical real estate driving and 30 on a highway trip. I've heard that 30/35 is more the norm.

JD

I'm always amazed when I hear people saying 35mpg. My '79 300TD non-turbo gets 21mpg or so on non-highway driving with petrodiesel, and

-tom!

I routinely got 26mpg with my 1980 300SD on long highway trips at 70. I used to make trips up to Boston, and remember that with the tank capacity of 21 gallons, there was just enough for a complete roundtrip, though I never did it, because I would run additional miles while in Boston. Around town here, which still doesn't have too many lights or traffic backups, it was a little less, probably because the lower speeds traded off with the occasional stops.

In the last six months, it dropped to about 21-22. I'm planning on replacing the injectors this Spring to see if that is the cause.

Check the fuel priming pump. I was suddenly getting worse than normal mileage on my '81 300SD. That pump was leaking hardly enough to be visible but enough to knock a few miles off the mileage. Fixed it then did a round trip from NY to FL and got 30+ mpg. Doing 20-22 around town now.

Thanks for the tip, but been there, done that. :)

In addition to the lower mileage, last Fall I started to have harder starting and rough idling problems. In the process of changing the fuel filters, after using the priming pump, that developed a leak, so I replaced it.

The fuel filter problem was the strangest thing I've seen. The only symptoms were harder than normal starting and then rough idling. It got to the point that it was shaking and almost stalling when stopped at a light, yet would do 70 down the highway with no problems. I can only guess that somehow with a clogged filter the fuel pump at ideal may not have been capable of delivering fuel, but at higher RPM it could? I could also rule out the leaking primer pump as the cause, because it wasn't leaking that badly so I was able to drive it with the new filters with the old primer pump and the idle problem was totally gone.

Anyway, pretty sure now there are no fuel leaks. No spots on the garage floor, no diesel smell. Also, the usual suspect fuel line return hoses are not leaking either.

I was going to take a look at an area in the driveway during the next light rain with the car running too, just as a final check. But, I'm probably going to replace the injectors, as that would seem to be the next logical step. The car has 125K with the originals.

I got 37mpg on my C280, with doubled horse power. I can beat e420 or higher easily. No kidding.