HI, Im new on this forum and definivily new at mercedes diesel, I did some reserch and found how incredible a diesel engine can be, I in the market for a mercedes diesel, I have some experince as a mechanic mostly vw and audi engines since I worked 2 years on a mechanic shop (perfomed all my maitenance), but never worked on a mercedes diesel (only vw tdi) . I would like your opinion about what mercedes would be the most reliable of these diesels:

1987 300sdl k98 Excellent
1979 300sd k87 Excellent
1985 300cd k71 Excellent
1984 300d k290 Excellent exept for (the dash board)

Anything with a OM617 engine will likely be more dependable.

Reliability in a used car is often a function of how well previous owners have kept up with routine service like oil changes, etc. Accordingly, one recommendation is to buy the car with the best set of service records and the fewest previous owners.

The first two in your list are S-class cars, a little bigger, more power goodies to break, etc. The six-cylinder 603 engine in the SDL is very nice, smoother and more powerful than the older five-cylinder 617 engines. Just don't overheat it and try to "make it home," you'll risk damaging the head.

The second two are E-class "ancestors" (the E-class didn't exist as a name until later) that are very popular on this forum. The coupe is less common (fewer built); mechanical parts are mostly the same as the sedan but there will be some unique body and interior parts that may be harder to get. Put a cover over the cracks in the dash and ignore them or get a junkyard replacement. The '84 is one of the best years for that model.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

This is a 2nd generation w126 with a 603 engine. One of the most reliable choices, provided it's been cared for decently. This, of course, is true for any engine.

Particular quirks of this one: as previously mentioned, head likes to crack when overheated, far more easily than other models.

Particular benefits: far roomier than any of the other choices, arguably the most horsepower.

This one's a w116. One of the most durable engines (the OM617 that everybody talks about so much) but perhaps (if it is a non-turbo) lacking in power compared to a turbo model. Somebody else has to help here, I can't remember if all or just some w116 longbodies got a turbo.

Since these have been around the longest off your list, checking for rust therefore becomes that many more years of a potential problem.


These two have the same venerable 617 turbo engine, again arguably the most reliable of the MB diesels. I'd recommend either of them. They're both w123 though, which could be small for your taste if the SDL appeals to you.


Food for thought: Your list completely skips one of the most popular cars on the forum, the 81-85 617-powered 300SD. It's the predecessor to the 300SDL, and in every way its equal. What it lacks in horsepower by comparison to the second generation, it regains in arguable durability. Take a look at some before you finalize your list.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

thank you all your feed back is great and very important to me

get a 81-85 300d or 300SD. These cars both have the 617 turbodiesel. They're both great but the w123 is built better , heavier, a little smaller, better exterior lines and incredible interior. It is a more classic looking car and was designed earlier in the 70's than the w126.


W126 has a different feel to driving it. It is bigger, gets 1 or so mpg better, has power seats which usually don't break, bigger trunk, more space under the hood (unless you need to get to anything heater related). The w126 has a more "ship" feel to it on the freeway that the w123 can't match. The w126 can also take a turn better than the w123 from my experiences.



The 78-79 300SD used a different body style. They had a 617 turbodiesel engine ( the first production turbodiesel car ever, i think). I haven't been around many w116's but from what Ive seen and felt its just a bigger, heavier car that looks like a longer w123. It has more chrome on it and has a great build quality. Interior is extremely easy to work on (mainly because tabs don't break off of everything you remove) and the exterior door handles are even solid chromed metal. The major buzzkill on these is the climate control system. The interior is good but still not as nice as the w123.

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1981 300SD 512k OM603

The '81-'85 W126 diesels (300SD) are very tough and durable, and easy to work on, perhaps the best of all the big W126 cars because of that diesel engine.

But with all of the old Mercedes diesels, you have to watch out for the dreaded tinworm (rust).

Depending on how bad it is, on a W123, W116, or a W126 it could be a surefire deal killer

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)

At this point condition is everything, so whichever one has a thick service book full of records and a caring owner(s). Its worth paying more for a better car.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

The 1998-1999 e300 turbodiesel is also worth looking at if you have you sights set on something "newer". The electronics and body may not last quite as long as the w116, 123, 126 are known for, but for the most part, the power plant is just as reliable.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL