I have a 1991 350SD Turbo that I recently put back on the road. The vehicle has 190k miles and sat for a period of about 2 years. I know the horror storied about this powerplant, however, the prior owner replaced all the rods - which I have for proof! He got fed up with the little things that were going wrong with the vehicle. With a little TLC, some major annoyances turned out to be minor repairs. The vehicle burns little to no oil and is a good runner.

I took the vehicle on a 600mile highway trip from Denver to KC. The vehicle averaged 17 to 20 mpg. I need to get the average back to where it should be for an easy highway trip.

I had the vehicle aligned before leaving, however, did not do it at a MB shop. In KC, I had an MB shop align the vehicle after replacing tie-rods that were worn. Alignment is much better, mileage a little improved.

When I got the vehicle the remaining fuel in the tank was pitch black and the vehicle smoked excessively. I drove the tank off, replaced all fuel filters and air filter and filled up with fresh diesel. That worked miracles and the smoke levels went down and idle smoothed right out. The engine timing was verified my a good friend at the MB shop.. He is the service manager there and doesn't charge me for those types of things.

Where i think I have a problem is actually figuring the mileage. The fuel tank does not consistently fill. For example, I can fill her up and drive 60miles. Upon returning to the station, I can only get 1/2 a gallon of diesel in her. I can then drive for 80 miles and bring her back and fill it with 6 or 7 gallons. Also, when I open the fuel cap, I hear a vacuum sound that I do not hear on my other diesel vehicles (300SD and E300D).

I am a long way from home and can't get under the vehicle. Is there anything that I should suggest that a mechanic do.

I figure I need to take care of this problem before I try to fix a mileage problem that may be nothing more than a weird tank. what else can I do to help mileage? I have new tires and brakes as well.

I am used to my '78 300SD which can easily achieve 27mpg at 75 - 85 mph. I'm not asking for the world but would like to get to the mid 20's consistently. Does it just need more driving because of all the time it sat?

Please help.

Richard