I've always been enthused about Mercedes diesels. Though I've owned nearly 40 vehicles in my 32 years, I've never had one. I recently accepted a position which requires a 40 mile commute, and my 11MPG Land Cruiser is costing me over $12 per day. I'm looking for a daily driver, and I'm thinking an OM617-equipped W126 300SD might fit the bill.

I've owned many BMW's, I'm no stranger to European cars. I realize if you take the time and spend the money to keep them maintained, you're often rewarded with a reliable car and an enjoyable driving experience. From what I understand, the OM617 engine is one of the most reliable engines ever made. How about the rest of the vehicle? What are the main shortcomings of this model? I do almost all of my own work.

I understand I could spend $2000 on a Honda or Toyota and get 40mpg, but as a car guy, I enjoy owning and driving vehicles I find interesting. Is it unrealistic to expect high 20's for highway mileage, providing maintenance is current? Are quality parts available at a reasonable price?

Lastly, car guys love to tinker, and I'm no different. I've heard these OM617 cars are notoriously slow. Is there anything that can be done, for a reasonable amount of money, aside from maintenance to return to factory output, to increase power and/or fuel mileage?

Thanks for the advice!

 

The W126 300SD will probably get mid-20's MPG, not high 20's, but under ideal conditions they should be capable of upper 20's. The 126 chassis is DIY'able and almost anything you'd ever need to do has already been covered in one of the various MB forums. You need to know where to buy parts online to get decent prices, and more importantly what brands of parts to NEVER use (i.e., Uro, APA, FEQ are all verboten; there are many others to avoid as well). The OM617 is not powerful nor fast but it can be modified to increase power, but not for a reasonable amount of money... the custom pump mods needed would probably cost more than you'd pay for the entire car.

Unless you are a large person and need a large car, I'd consider stepping down to the mid-size body (300D), or even the small (190D). And if you are willing to move up to a newer engine (OM602/603, or even OM606) the fuel economy and refinement all increase dramatically. Something like the 1987 or 1990-1993 300D, or 1995 E300 (W124 chassis). All are capable of MPG in the low 30's and are faster than the W126 diesels, and yes they are still easy DIY repairable. The 190D can get mid-30's and even low 40's with a manual tranny and the smaller 4-cyl engine, but they are slow, and it's difficult to find one that isn't beat to death.

The W210 diesels (1996-1999) will increase power & MPG a bit over the W124, but they are slightly more difficult for the DIY'er, you will need a digital scanner and know how to use it. And the W210 is more of a fancy Toyota than a Mercedes. If you want a newer S-class, be careful... the 1990-1995 350SD, 300D, and S350 all have the infamous 3.5L "rodbender" engine. if there is no documentation showing a rebuilt engine has been installed, and/or the owner mumbles something about having to add oil periodically, run away. The 92-up will be the W140 chassis and is also a bit more complicated for the DIY'er, similar to the W210... but the W140 is a rolling bank vault. Amazing car, too big for my tastes, I own a long wheelbase W140 and plan to sell it.