Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Overheated diesel engine replacement

A couple of weeks ago the diesel engine in my 1981 300D Mercedes overheated. It was checked out by a local Mercedes Dealer service shop and I was told that the engine was running dry, without coolant and that the engine would probably need to be replaced. I had the car towed home and I am leaning towards repairing or replacing the engine. The condition of the car is good and clean condition. My question is should I consider a used engine, a rebuilt engine or a factory re-manufactured engine. And should I consider a local auto repair shop, an antique car restoration specialist or a Mercedes Dealer service shop?

I would check around and see what’s available. A used engine is probably scarce. A rebuilt may be possible as well as a factory rebuilt. I don’t think you need a antique car restorer because of the relatively young age of the Mercedes in vehicle years. A Mercedes dealer shop is out of the question in my mind. I would check on the possibility of rebuilding your engine but it may be in bad shape internally. The only way to tell for sure would be to tear it down and inspect it.

A 1981 Mercedes diesel engine is going to be rare to find. In this case, start with a car restorer. If anyone has one, a restorer will know where it is.


Ahhh, what do they know? Your old oil motor bears very little resemblence to anything sold by Mercedes in this country for a very long time. Ideally, you should see if there’s an independent Benz specialist or at very least import specialist somewhere in town you can take it to.

Did the engine quit running because of the overheating? Or did it just overheat, you shut it off and had it towed in?

I doubt momentarilly overheating will kill one of these incredibly stout engines, even if all the coolant leaked out. Unless the engine is honest-to-goodness siezed up and won’t turn at all, I would definitely insist on a compression test before you even consider discussing a new engine. Who knows if a modern Mercedes dealer even do a diesel compression test?

If it is really shot, definitely try to find a used engine-- they’re actually not as scarce as you might think because the transmissions typically don’t last as long (granted you might get an engine with 300k on it, but that really doesn’t matter on these cars). I priced out an aftermarket rebuild kit for my old '80 240D a few years back and it was a lot more than I paid for the car-- I don’t dare imagine what a factory rebuilt engine will cost!

I found several sites for used 300d engines. One offers a 3 year warranty and free shipping for about $2200. Just google for more sources. Here is the website:

I have heard of this site but have never purchased anything there. Let the buyer beware!

Those are pretty tough old motors…Have you tried to get it running? Are you SURE it’s shot??

If so, in a 27 year old car, a used engine is the only thing that makes any sense, or walk away…

One thing you learn in the automotive repair business is, you never purchase a major replacement component unless you look, feel, hear that component. And on the internet, you have to pay the shipping back if that component takes a crap.


Time to do a Ford 5.0 SEFI conversion… :slight_smile:

Seriously, if you’re planning on keeping the car I’d go with a rebuilt or reman engine from someone local and preferably from someone who services Benz cars.
It’s been my experience from dealing with used components (engines, transmissions, rear axles, etc.) that about 20-25% of them have issues ranging from minor to scrap iron.

I’m still seething over a “guaranteed good” rear axle that was “partially diassembled and thoroughly inspected” from a local yard that has been in business for 50 years and with whom I’ve dealt with a number of times.
That axle was scrap from one hub to the other and to make it even worse; when returned they presented me with another rear axle that had been “tested”. It was only half junk so there was some improvement.
They lost a 20+ year relationship with me over that one.

Thank you for your response. The engine quit because of overheating. I did not shut the engine off since it shut off on its own. The Mercedes-Benz service shop where the car was towed told me that the engine was blown, that the radiator and coolant system was dry and that the car must have been running dry for too long. I had very little warning of any problem. I was traveling north on I-476 about 55-60 miles per hour when first I felt the engine slow, I smelled burning metal, smoke came from the hood, smoke came from the back (exhaust?) and the temperature guage, as usual showed a hot engine. All in about 40 seconds before the car stopped. Back in Philadelphia my mechanic of ten years had told me in January after the annual inspection that all fluids were checked, including the coolant system. I have not heard of a “diesel compression test” but with what I’ve just written does that still seem necessary?

Thank you for your response. I have recently put the ignition key in and tried to start the car; I hear the electric system but the engine does not turn over or even respond.

A compression test just measures how much pressure the pistons are exerting on the compression stroke. It’s basically a way to test the internal condition of the engine-- if the rings are worn or there’s damage in the valve train the pistons don’t seal well and don’t exert as much pressure. If the compression is low, it can also hint at what the problem is. Since diesels have much higher compression ratios, the testers you use for a gasoline engine usually don’t work so you need someone that has a diesel one, so a regular mechanic (and possibly even a modern-day Mercedes dealer) might not have one.

Like I said above, if the engine is really siezed up, as in in won’t turn at all (the mechanic should try to turn the engine with a hand tool), it’s junk. But if you can even get it to spin, it would definitely be worth doing a compression test and, depending on the results, possibly a leak-down test (this is another test that can tell you about the internal condition of the engine). Even if there really are serious engine problems, depending on what they are it might make more sense to repair what you’ve got in there than to replace the whole engine.

try filling it with fresh oil and new ainti freeze and she if she runs…my 300 gets hot. do not buy a re-con engine, buy a second hand or new if funds allow, mine as done 400,000 miles and is sweet as…

EBay has an engine as of now for $1300 with 126K miles. I would want to go see it run and if OK, haul it home on a trailer or with a pickup.

The dealer said it was running dry and would probably need to be replaced, but what does that mean? Does the engine still run? Does it have normal acceleration and no mechanical noise? (other than normal for a diesel) Why is it ‘dry’? Is it just a leak?