Old Mercedes 300D


I’m looking at 75 mercedes 300D, 290k miles with a supplemental fuel system to burn vegetable oil from greasecar.com. Seller says he can demonstrate contiuous good maintenance. What sort of maintenance demand can you expect from such a beast, and how hard are the simple tasks like brakes, shocks, replacement alternators/starters, etc?

Oh, what’re they like to drive. I’ve driven volvo 240’s forever, so I’m used to something that’s a bit of a lead sled.


As good as the 300D is (or was) it’s a 30+ year old car with nearly 300K miles, and nothing lasts forever. The good side is; Mercedes is one of the few makes that you can count on being able to get parts for, as long as you’re willing to pay for them.

My guess is that, since it’s been modified, many mechanics will shy away from it. The standard mechanical stuff, brakes, alternators, etc., should not be any more difficult than on any other car. If the car does not come with a service manual, I suggest you purchase one (try Books4Cars.com), because you will need it if you are going to work on the car yourself.

I hope you’re not planning to pay much for this car, because, veggie burner or not, it just isn’t worth very much. Good luck, and if the current owner doesn’t have a thick stack of maintenance records, he can’t demonstrate anything.


It’s all about the car’s condition, although I personally wouldn’t buy one with a WVO conversion. They will run indefinitely provided they are well maintained and do not have significant rust issues. The '75 300D is a W115 chassis, which is very nice looking, but a little more prone to rust than the later W123 chassis. The WVO would scare me off, there is a potential of damaging the injection pump (about $1600 new, $900 rebuilt) if poor quality oil is used. I would look for one without the “conversion,” and have a good pre-purchase inspection performed by someone who really knows these cars.

I drive an '82 300D with almost 400K miles and also have an '83 240D with a little over 200K miles. One weak point is the automatic transmission, my 300D needed a transmission replacement at about 250K miles (plan on at least $3500). Plan on spending a few $100 to a couple $1000 per year for routine stuff, still much cheaper than a new one but more expensive than a ricer. Regarding the value, I have seen them sell from $1000 (junk) to $25,000 (show condition). A good driver might cost $5 - $10,000 on a car lot, or a little less in a private sale (a friend of mine just sold a pretty decent '84 300D (turbo) for $12K). I wouldn’t be surprised if you could find a pretty good W115 300D for $5000, or so.

These cars a pretty easy to work on, unless you need serious engine work. Things like alternators and starters are about the same difficulty as any other 70/80s car. Parts can be expensive, but they are widely available, plenty of after-market sources and the dealers can get anything you need (for a price). If you do need an engine rebuild, plan on spending $5000+ for a good quality job.


Yeah, my mechanic told me not to involve him based on the age Asking price is $2500 w/ WVO. Owner claims 5 years running w/ WVO, and some bubbling in the rear quarter panels.

I’ve been looking to get into WVO and what I’ve been able to find for pre / post conversion cars falls into two tiers that overlap in the middle- Old mercedes, (75-84)to the left of $6K and newer VW’s, (90’s-present)well to the right of $6K. Since a WVO system, which presumably could be stripped for reuse is $1K, it seems like a reasonable risk.

How hard is it to keep on top of rust? I live near Buffalo, and they put salt or Calcium chloride down, depending on where you drive.


“These cars a pretty easy to work on, unless you need serious engine work. Things like alternators and starters are about the same difficulty as any other 70/80s car.”

I must disagree with that statement. They are a pain in the A$$ to work on. At that mileage, it’s WELL past prime…Bubbling in the rear quarters?? The rust is already extensive. Lift the floor mats and look for daylight…


I agree with the rust concerns, I would not buy a rusty one. You really need to determine if it’s surface rust that can be repaired for a couple of $1000, or if it’s structural rust would cost too much to fix. If you don’t correct the rust it will eventually be fatal.

Why do you think they are difficult to work on, have you owned one? The turbo 300D is a little congested on the right side of the engine, but not too bad. The non-turbo 617 engine is a piece of cake, there is a ton of room around the engine, sorta like a 60/70s domestic. Just about anyone can change an alternator or starter on one of these, however removing the top starter bolt on the turbo 617 can be “challenging.” These are only “past their prime” if they’ve been neglected, my 400K engine is still a long way from needing a rebuild.


Just wondering why you are interested in running WVO, if you are just trying to save money buying a 30 year old car is not the best way to do it. Most folks that drive these consider them an (expensive) hobby, so folks just run them into the ground (but they aren’t around very long). Buying a late model VW will probably be considerably cheaper in the long run. Personally, I don’t think running WVO is a great idea. BTW, are you planning on running WVO in the winter in buffalo? If you are doing it for environmental/political reasons, why not just run commercial bio-diesel?

The original purchase price of $2500 will be irrelevant to the total cost of ownership, just fixing the rust/paint will probably cost more than the purchase price. Also, I wouldn’t drive a W115 in salt and expect it to last very long. If you just want to experiment on one, find a $1000 beater and don’t bother trying to preserve it.