Purely from the point of view of the engine itself and not anything else to do with the car. My opinion would be OM616, followed closely by the OM617 NA.

Valve adjustements are not an issue if you are mildly handy with a wrench.

However. All of these engines are now over 40 years old and most have many hundreds of K on them. So inevitably the inherent reliabilty has started to diminish simply thru age and extreme distance.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

The engineering is decades old but some are fresh rebuilds and there are brand new om616 and 617 engines being manufactured even today.
Personally I think it’s still I viable engine. I may falsely conclude that modern diesels are higher performing and less reliable. I’m not an engineer but the market is performance driven and a business model over engineers a product for reliability, profits are in jeapordy. Perhaps evidence of that can even be observed in the 617/617 by considering the cam chain? Why use chains and sprockets? Wouldn’t geared timing be less prone to failure and increase service intervals? Regardless, we continue using them because they have value. Hoping for refinement is an exercise in futility.
Some value reliability over performance but they are far outnumbered by those who value, demand, and expect increased performance. The biggest complaint and target for ridicule the 200 series diesels are subject to is their lack of power. I think that’s ludicrous. It gets me where i’m going and I’ve never had trouble reaching any posted speed limit. I’ve never been on a race track and I personally don’t expect towing capacity from any sedan. I expect it to transport a small family while loaded with enough groceries to feed them for 2 weeks. I expect operating and maintenance costs to be reasonable. And lastly I don’t need or want to trade it in every 5 years for a new one. A 240D more than meets those needs and will do so for anyone who isn’t encumbered with the status quo. It is what it is and that’s more than enough for me. In truth, if these engines never required any maintenance I’d probably get something else because i enjoy the process.

My vote would be the OM606.910 w/ 4-valve head in the W124. Greatest chassis probably ever made or at least the last of the "overbuilt Mercedes". Got mine up to 110mph going to Colorado a few years ago. Add turbo and it will be way faster than I'm brave enough to drive.

I've only got 170,000 on mine, but my buddy has two that he bought for $500 each and has put 240K and over 315K on each separately.

I'm still hoping to make mine into a diesel W124 "Hammer" by adding a Swedish rebuilt fuel injector pump, upgraded injectors, a Finnish built turbo manifold and just bold on a pretty standard turbo off a Cummins and double the 134hp, and the 155 ft-lbs or torque to 268hp and 310 or more ft-lbs of torque with almost no other changes. Of course the N. Europeans are getting huge power out of their old Mercedes diesels by tweaking them for drags and ice racing, but I want reliable with good power. Like to plug the later 5-speed auto in if I can as well. Dream conversion.

Great style, chassis, reliability, economy and decent power even normally aspirated.

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JR

2008 Mercedes E320 BlueTec, 77,000
1995 Mercedes E300D OM606, 167,500
1996 Moto Guzzi Sport 1100 3,000
1994 Mercedes S350 TurboDiesel 113,000 (rebuilding engine)
1976 BMW 2002 (being rebuilt with 1975 interior)
1975 BMW 2002A 156,000 (donor for '76)

International Harvester's 6.9 and 7.3L IDI's were rock solid in the 80's.

The fact is, any real diesels made in those days were industrial tough, had few emission standards to worry about and ran without electronics or computers, so they were all pretty awesome.
The only car maker to somehow mess that up was GM - almost like it was on purpose.
Yep, General Motors was really ahead of their time.

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1985 300TD 1981 Scirocco 1.6D conv 1986 Golf 1.6D 2003 Golf TDI

The ford cast 6.9 blocks were prone to crack from one cylinder down through one of the main bearing webs. The international cast blocks interchanged with the fords but did not crack.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

so here I am again, I haven't seen the last answer, but I have too many doubts regarding the longevity of these engines... some people say the 616 is more reliable and lasts longer, some other people say that the number of cylinders doesn't matter (a om617 could last as long as a 616, if not even more)... I'm starting to think that it depends from personal experience

They're all the reliable enough, within margin.

What you need to concern yourself with is the maintenance and ownership of the humans involved with these 40 year old machines.

You need to buy from the right person above all else.

I agree with you the 603 with an update head is the best engine no electronics I own two 603’s my daily driver has 111,500 miles on a rebuilt 603 with a #22 head and after the rebuilt I have done nothing to the engine. And my second 603 has a #20 head I just replaced the head a few months ago and is running great. I’m working on my third 603 to is going to have a #17 head and is going into a W201 190D

It really depends on your usage. If you drive more than 12K miles a year, you probably don't want an OM61X motor. You need to change fluids every 4K miles and adjust the valves annually. Preventative maintenance and OE parts are key to their trouble free nature. I own a W115 240D and W123 300D, both in their most desirable spec (last year of production, EU spec cars etc.)

If you need a workhorse, get a newer car and run it into the ground. If you want something for recreational use, a post '82 NA 300D is your best bet.

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Why I will never do business with "DieselKraut" again

http://www.peachparts.com/shopforum/mercedes-benz-used-parts-sale-wanted/378935-why-i-will-never-do-business-dieselkraut-again.html

oh, shoot...still, I cannot understand which one should I buy; of course, I don't want any turbos; seems that the reliability and longevity of a 300d is the same as the 240d, since (at least in EU) that the 300d doesn't have all that doodad's and bull**** some of you guys talked about in other discussions; but, the fuel economy is something that could make most of the people choose the 240d over the 300ds, because, especially the pre-restyling ones, they needed about 10l/100km (thanks to the 4 speed trans, too)

Consider the fact that this 3.0L NA diesel was originally designed by Daimler as a TRACTOR engine.

It would be the perfect engine for any vehicle that never went above 100 km or 65 mph. Especially with an MT

Does that fit what you do?

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Strelnik
Invest in America: Buy a Congressman!

1950 170SD
1951 Citroen 11BN
1953 Citroen 11BNF limo
1953 220a project
1959 180D
1960 190D
1960 Borgward Isabella TS 2dr
1983 240D daily driver
1983 380SL
1990 350SDL daily driver alt
3 x Citroen DS21M, down from 5
3 x Citroen 2CV, down from 6

Ok, I'll be that guy....

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

My 300 na euro would go 100 mph in either fourth or fifth and cruise all day at 75. If it was originally built for a tractor who cares? The TR3 gas motor was tractor based too. TR even used a tractor or truck tranny in the TR3 too with the shifter blocked off the granny first gear and added OD to make it live happily on the road.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Yes, they're a great engine, I have two.
Just many out there say "it's an industrial engine put in a car" or "tractor engine". Yes they were used in industrial applications, but they were a development from a long line of 4 cylinder automotive engines. The turbo variants were the end of the line, although the Indians still make them with modern updates.

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD