just posted my first mpg results!check it out!
 

1986 mercedes benz 300 sdl turbo diesel, 142,000 miles . drove 164 miles used 6.1 gallons. = 26.89 mpg! hope to improve and maybe reach 30 mpg.
check it out in the garage.:)

I have a 1986 300 SDL myself. It currently has Goodlear Assurance fuel Max 205/65R15 LRR tires on it. It got just a tiny bit over 30 mpg with freeway driving between 65-70 mph, and more than 40 mpg at a steady 50 mph. It gets less than 20 mpg in the city though.

I'm planning on turning it into a 45 mpg highway, 150+ mph top speed machine. This will entail a much taller rear end and/or wheel/tire size and lots of aerodynamic work. City mileage won't change much, but lots can be cheaply done to improve highway mileage.

Congratulations! :cool:

I'm always pumped up when I reach a new (for me) milestone when trying to acheive greater things. As you practice more of the concepts you pick up on these forums and from other folks success, I'm sure you'll reach that next milestone.

Can you estimate your extra mpg with these tires? Do you leave them at factory spec PSI since they are for fuel economy or did you still pump them up to/over side wall max?

Goodyear Assurance Fuel Max 205/65R15 tires on my 300 SDL has increased the fuel economy at a steady 70 mph from 28.5 mpg to 30.1 mpg. This was measured on a trip from Corpus Christi to Falfurrias and back; the previous tires used on that same trip were identical in size, and very old with little tread left on them(Warrior brand). I got 40 mpg at 50 mph with the old tires, and not the LRR ones.

Driving from Texas to Oklahoma, it got a bit over 30 mpg as well with speeds between 65-70 mph, and from Oklahoma to Missouri, got 26 mpg doing 85 most of the way with some sprints to more than 110 mph(with the turbo not dumping pressure into the engine any longer; see below).

However, I had no indication of wind speed and direction on the two identical trips, which could drown out measurable effects.

I'm intent on eventually going basjoos with this car and installing perhaps a 2.44 rear end from a similar Mercedes model, if it will fit(I know a 2.65 will fit for a fact, but the gain in top speed would be too small for my liking). I will also be sending off my injector pump to Myna out in Finland, so it can be upgraded with 7mm threads. I'm aiming to get a modest 220 horsepower/290 lb-ft of torque out of it, enough to have some fun, but not enough to break stuff. Parts for these cars are very expensive! 0-60 in 7 seconds, with 60-100 in 6 seconds, would be a reasonable goal with this car. Stock, with 0-60 mph being a tepid 11 seconds, it pulls like a car that does 0-60 mph in 7 seconds on the highway over 50 mph, at least when the turbo worked. A sensor that detects an overboost condition got clogged with soot, and it is in need of replacement; since the turbo stopped putting boost into the engine(it still spools), 0-60 mph has become a tepid 19-20 seconds, although on the highway its acceleration about matches a 2003 Cavalier.