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Mercedes 300D? Yes or No?

My wife wants a 1984 Mercedes 300D. She’s been checking craigslist and the papers daily. My problem is that I have no experience with Mercedes or diesels so before she finds that perfect one does anyone have any advice for me?

Should I talk her out of it? (like I should have done when she fell in love with and bought an old VW van- she still to this day gets on my case because I didn’t stop her!)

We do have a good Mercedes mechanic in town but I’m worried that the car would be spending more time with him than with my wife.

If you can find one that has been taken care of, sure. Definitely take it by your Mercedes mechanic and get it checked out before buying. It seems like every 300 diesel that I see has a black streak up the back and a perpetual cloud floating behind it. I have to assume things like injection pumps and things of that ilk are spendy spendy on these cars, so it would be well worth it to bring it in before you buy. If you’re thinking of going the eBay route, I would NOT buy one sight-unseen.

If her intent is to be economical, then buying a Mercedes diesel is a plan to save money no matter what it costs to do so. Compared to a modern mid size car, the fuel mileage is not anything to get happy about. Other than that, a diesel car is unique which may be a positive attribute to some.

You really need to know what you are buying. I have a couple of benz diesels, my daily driver is an '82 300D with over 400K miles. They are great cars if they are properly maintained, if you buy one that has been neglected you will spend a lot of cash getting it into good shape. Have the car checked out by a good benz shop and get an estimate to fix everything that is wrong with it before making an offer. Even a good one may need a couple of $1000 of attention to make it perfect. I don’t know how many miles this car has, but you need to start paying attention to the automatic transmission in the 200-300K mile range (I replaced mine at about 275K miles, about $3-4K for a good rebuilt), be aware of any “flaring” between shifts. Also, verify that the car has no rust, do not buy a rusty car for any price. Do not believe that the AC “just needs a charge,” that usually means about $1500 worth of work. I would also avoid any AC system that has been “converted” to R-134a, it will be expensive to change it back to the correct R-12 coolant an get good performance (I made that mistake). Plan on spending about $500 if the cruise control isn’t working correctly. Also, be aware that they require valve adjustments every 15K miles (about $150 each).

Expect to spend in the $5-10K range for a good driver (not a show car), and don’t be surprised if it costs you about $1000 per year for the usual “old car nits.” You may find a good one for less money, but have it checked very carefully. Also, the realistic fuel mileage is in the mid-20s, these are not economy cars (they weigh about 4000 pounds loaded). Don’t let me discourage you, these are very cool cars, IMHO they are the last of the high quality benz sedans. However, do not buy one if you are trying to save money. They are less expensive to own/operate than a new benz, but there are many late model cars available that are much cheaper to own.

" We do have a good Mercedes mechanic in town but I’m worried that the car would be spending more time with him than with my wife."

You would be correct…

Nonsense, I drive mine about 40K per year with very minor issues. I routinely drive across country (800-1000 miles per day at 70-80 mph). A 20-year old (well maintained) 617 engine is at least as reliable as any of the current rolling video games.

No, under normal conditions they are very reliable even at that age and miles. They do take some care, but they were one of the most reliable cars made at that time.

All the above advice is good. Glad to have some MB owners relate their experience. A VW van is probably the worst van ever made for sale in the US. It takes a complete masochist to keep owning one. I’m curious as to why your wife ever wanted such a car.

As to the Mercedes:

If she is environmentally conscious, this car both pollutes more and uses more fuel than a good compact car of today.

If she’s worried about safety, modern cars have many more safety features.

If she wants to minimize operating costs, a 4 year old small car would be your best bet. As other posters pointed out, the fuel mileage is not great and the maintenance upkeep will wipe out whatever other savings you have.

If she wants reliability, even a Toyota Echo is more reliable than a Mercedes.

It would seem that the only reason for wanting something this old is to be different. The only people I know who successfully drive these old MBs are very knowledgeable car guys or Germans trying to cope with homesickness. Both are prepared to learn a lot about their vehicles and treat it as a dear pet. The Mercedes will certainly be more reliable than the VW van, but is will be a project car for you to look after.

I agree with much of what you’re said, but a couple of very good reasons to drive one of these is to avoid the “safety features” of modern cars and to avoid driving a “good compact car of today.” I will take a 4000 pound car made of real steel, with real brakes (no ABS), over any “modern car” in an accident. Check out this video and tell me which car you would want to be sitting in (the W126 in the video is a little bigger than a 300D, but the construction is nearly identical):

I agree that you can save a lot of money by working on these yourself (they are actually pretty easy to work on), but you can preserve one very nicely with a good independent shop. Realistically, I spend about $.30 per mile to operate/maintain mine, compared to about $.50-.60 for a new benz (and the new ones are no fun to work on). These are a bit of a hobby, but IMHO they are much cooler than anything available today.

Thanks for the reply. If mass and safety were the issue my old 1988 Caprice was very safe indeed. I reluctantly parted with it after 19 years of faithful service. A guy down the road has a late 50s British Humber Super Snipe, which looks like a shrunken 56 Buick Super. It’s nearly impossible to find parts for this car, and he only drives it in the summer. It’s a really cooool car! If I wanted something cool and different, and had a 3 car garage, it would be a late 80s MB 300 Turbodiesel. But strictly as a hobby car.

“it would be a late 80s MB 300 Turbodiesel. But strictly as a hobby car.”

Personally, I’m not a big fan of the late 80s 300D (W124), but there are plenty of folks driving them. If you ever buy one, be very careful not to let it overheat ( the aluminum head really doesn’t like it). There are tons of older cars I would like to own, all it takes is time, space, and money. The best part of the old benz is that parts are not an issue, the dealer can get you just about anything back to the 50s, and there is a very strong after-market. Your '88 caprice was probably pretty safe compared to current cars.

The Mercedes 123 chassis is considered by many to be one of the best cars ever made. It is certainly one of the best cars Mercedes ever made. The 300D turbo diesel is, in my opinion, the pinnacle of the 123 line.
At it’s core is it’s basic engineering and it’s simplicity. These cars do not have all the whiz bang technology of the later models. Just a rock solid body and engine combination that can easily last a half million miles with basic maintenance.

The real killer on these cars is rust. Start with a vehicle that has a rust free body and under carriage.
Next, run a compression test on all five cylinders. Good compression is paramount on a diesel engine.
These cars use vacuum extensively. The vacuum lines become old and brittle with age and can cause all sorts of gremlins from door locks to engine shut off. Fortunately the vacuum system is (relatively) easy to diagnose and repair. Vacuum lines, elbows and T’s are easy to replace. Even if the vacuum pump is worn out, it’s not a bad repair.

The valves need to be adjusted every 15k miles. This is critical for cold weather starts and smooth running. If you can’t document the last time it was done this should be performed right off. Expect to pay about 2.5 hours of labor if done at a shop, but it can be a DIY job with the right wrenches.

There is an upgrade for the glow plug relay that makes for much better starts. The light on the dash can tell you a lot about the condition of the glow plugs themselves. If bad, I like to replace all five.

The air cleaner bracket seems to fail on all these cars at some point and should be checked out. New parts are readily available and easy to install.

The engine should run smooth and (relatively) smoke free if everything is in spec. The injection pump is rock solid and rarely fails, but it is the first place most non-Mercedes mechanics point to during diagnoses. A good clean fuel system is a must. There are three filters for the fuel system. The in-line and spin on filters are under the hood and are easy to change. I’d recommend twice a year. The third filter is often overlooked. It’s the strainer filter located in the fuel tank. If algae is growing in the tank it will clog this filter and cause all sorts of problems. You can chemically kill the bugs, but the dead bugs will clog the strainer. The best bet is to remove the tank and have it cleaned, and then replace the strainer. Then buy only the best fuel from a busy station where the fuel doesn’t sit for long periods.

All in all, these are very good cars and can last a very very long time. They’re not hard to work on and any part on the car is readily available. Get the car up to speed on all maintenance and then keep it that way and you’ll have a very enjoyable Mercedes experience.


“There is an upgrade for the glow plug relay that makes for much better starts.”

Good point, that was probably the best/cheapest investment I ever made on mine. It makes a world of difference in cold weather.

Thanks for all the advice. I talked to the Mercedes mechanic in town today and he prefers the 240D over the 300D. He mentioned that the air conditioning system has fewer problems and it’s easier to work on. He actually recommends Toyota for the most reliable car but my wife just loves the look of the 123 body and is interested in using biodiesel. We’ll see what comes along.

I have one of each, a '82 300D and a '83 240D, and they are completely different beasts. The 300D has about twice the power of the 240D, but the 240D is much simpler. The 240D is a great “around town” car but it isn’t really suitable for current highway speeds, they were sold when the U.S. speed limit was 55 mph and they are not really happy above about 70. The 300D will cruise all day long at 80+ mph without a problem, but it feels a little heavier around town. The 300D has a little higher level trim and an automatic climate control system (very nice once you get it sorted out, but a little expensive when the electronic brain decides to die), the 240D has manual heat/AC controls which never break down. The AC systems are both R-12 and do not perform very well when converted to R-134a, so be prepared to pay about $60/pound for R-12 if it develops a leak. Also, some parts are getting expensive, I recently paid over $500 for a “dealer only” AC hose for the 240D.

Also, benz only recommends bio-diesel up to B5, although lots of folks are using B100. There are some issues with fuel lines when using straight bio-diesel, and you can only use it in warmer weather. If your really interested in benz diesels, check out this forum (serious geeks, including myself):

BTW, try buying parts for a 25 year old toyota sometime.

Just replacing the power steering pump belt is an all-day, $150 job…

BTW, try buying parts for a 25 year old toyota sometime.

A valid point.

Does anyone know if I could pull a light weight trailor (light load) with a 300D? The wife’s on a mission!

“Just replacing the power steering pump belt is an all-day, $150 job.”

Have you ever opened the hood on one of these cars? I can literally replace the PS pump belt in under 10 minutes (3 bolts and an adjuster), including the time to take out the tools and wash my hands when I’m done. Last year I replaced all four belts in a parking lot in about 30 minutes (after the inner belt broke in the middle of VT).

AFAIK, the factory does not give them a tow rating, but I’ve seen a few of them with hitches. I wouldn’t try to tow anything heavy, maybe a small 500-750 pound trailer with very little hitch weight?