Yes there have been a lot of discussions on this already. However, there are still 2 things I'd like to understand.

*I'm talking about these engines in the W126s 1981 - 1987 (OM 617 D 30 A & OM 603 D 30 A )

1. How do the engines compare noise & vibration wise? I haven't found much useful info on that

2. How bad are the issues with the OM603.96x?

Wikipedia: Even without the heat from the trap oxidizers, the original #14 mold cylinder heads were weak and if overheated could crack as with any overheated engine. In general, the later model #18 or #22 mold cylinder heads are considered to be the definitive cure for cracked heads. - TRUE?

I would assume virtually all of these engines still alive today should have had the particle filter removed by MB and other parts damaged should have been replaced in the last 30 years. Isn't that right? Still looking for a conclusion about the engines reliability...

87 was the best year for the 603. So the 603 had a head issue. Catch the problem before it progresses and you're fine. Who cares about noise? If the car is properly tuned there shouldn't be any to little vibration at ALL.

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97 W202

For a 5-cylinder engine the 617 is remarkably smooth. Don't let vibration concerns keep you away from a nice 300D or 300SD with a 617 engine. I was quite happy with my '85 300D-T.

The 603 head problems have been overblown. Any engine with an alloy head can have problems if overheated. Folks would have a cooling problem and instead of immediately stopping they would try to "make it home" and crack the head. The earliest (#14) head also has some risk associated with insufficient space between oil and water passages. If you buy a car with a 603 engine, try to get one with a #17 or newer head. However I never had problems with my #14 head.

In terms of basic maintenance the only difference I remember is that the 617 engine needs regular valve adjustments while the 603 has hydraulic lifters that are self-adjusting.

In general, the 1987 300D Turbo with the OM603 engine in the W124 chassis is a far more modern car than the 1982-85 300D-T with the OM617 engine in the W123 chassis. The 124 has a driver airbag, ABS, much better suspension, and is a little quieter and smoother than the older car. By comparison, the 123 is much more the "classic" Mercedes, probably the last of which one can say that. It also drives like a tractor (said my wife).

No matter which one you buy, try for the best one you can afford. A cheap Mercedes is no bargain and you'll have many chances to regret it. The 124, a later model with more sophistication and more goodies, has more things that can break. If you can do your own work this is not such a big deal but a Mercedes is an expensive beast to have others work on for money. This is true of any Mercedes -- the money you save on the purchase price will come back to haunt you many times over. Look for a car with a complete set of service records.

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

Jeremy - please tell me more about the "The earliest (#14) head also has some risk associated with insufficient space between oil and water passages." statement. I have done a lot of reading on here, but hadn't seen that particular mention before. I have an '87 that's got some oil traces showing in the coolant but none of the other cooling system issues. Yes, it's a 14 head...

noise, the 603 wins hands down. I have NEVER gotten any drive through problems with the 603. I nearly always have to shut off the car in a drive through with the 617.
vibration? in perfect tune, they are very similar vibration wise. if the car has vibration in a 617, it needs something. either valves adjusted (which the 603 never needs) or injector problems *(fuel filters can cause vibration as well as motor mounts)

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My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
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Its critical to note the 603 REPLACED the 617. Mercedes isn't stupid, they wouldn't have spent millions in development, R&D, testing, etc to build a motor less modern than the last.

Do you know what is smoother than a 603? A 606.

Do you know what is smoother than a 606? an E320CDI.

Do you know what is smoother than a CDI? a new V6 Bluetec Car.

Its progress. The motors get more complicated which is probably where they get a bad rap as certain things are harder to do in your garage, but the fact of the mater is the 603 is a more technologically advanced motor than the 617.

I did all the filters on a 617, ran injector cleaner in it, verified the timing, and we had the dealer adjust the valves, the 617 can be very smooth.

And with leaking delivery valves a 60X can be hilariously rough.

Either motor, if its a healthy motor and you are up to date on maintenance it'll be a nice car. But that's true of most cars.

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I've seen pictures in this forum showing broken head gaskets or internal leaks at the front of the block where the clearances are to tight on the #14 head but I don't have copies of those pictures -- you'll have to hunt for them. I replaced my #14 head with a #20 but didn't have problems with the #14. I was fixing an external oil leak that was related to a poorly-installed gasket and the switch to the #20 head was just because it was available. I'm sure there are others here who can give you the detailed information you are seeking. Try a search of Diesel Discussion with "#14 head" as the search term.

Jeremy

__________________

"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 good post and very accurate. I've owned many 617s and I love them, but a good OM603 is a much more refined engine with more power and torque. I had a 1987 SDL for a time with an excellent engine and transmission, (it also had a later #22 head), it was very sweet car that I miss.

I've also owned OM617 powered cars in great condition, (both w123 and w126), they are fantastic but technology marches on and the jump from the 617 to the 603 was one of the biggest jumps forward in diesel refinement for MB. The problem, as stated before, is that no engine with an aluminum head takes overheating very well. The OM617 is a cruder power plant and has a cast iron head that is very tough. I've seen plenty of people kill an OM617 as well, usually from lack of lubrication from oil leaks and not checking oil, (or running SVO and ruining engine), but they will survive the occasional overheating that the later engines will not.

Any of these engines in good condition that has been maintained and not overheated will be great. The problem is that as the cars get older, they fall into the hands of less affluent owners who either can't afford to service them properly or don't care about the car anymore. An OM617 will take a hell of a lot more abuse and deferred maintenance than an OM603. If you can find a good OM603 car, they're awesome and can run forever with proper maintenance.