I recently got my 420SEL running well, and am starting to understand why you guys are so enthusiastic about M-Bs. Manischewitz, that engine has a lot of power, and it's so smooth! Also, I'm not used to a large car that handles so well.

But I still have a couple of questions about the M116 motor. If I am not mistaken, this engine was produced from 1979 to about 1990 or so. Was it introduced with an iron block, and then later switched over to light alloy sometime during its production run? (Of course I know that my car has the M116.965 alloy block.) If so, when did that occur, and what are the differences between the two versions? Were any other significant changes made to the M116's specifications during its production run?

I'd appreciate it if somebody might know of a link that might cover this.

The M116 engine came out in 1970.
Was cast iron 3.5L until 1981 here in USA.

There were 3 different sizes 3.5L, 3.8L, & 4.2L. The 420SEL was discontinued in 1991.

The engine went thru 3 different fuel systems & many other emission changes.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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Thanks very much for the information. I think we may have gotten lucky with our $500 Mercedes. (Of course, our total investment is now about $2,000, but it is running rather well at the moment.)

The 4.2 and especially 3.8 M116 are somewhat slower by today's standards, but they are very easy to work on and will run forever with very low maintenance costs. Just make sure you do your guides every 100K and keep an eye on the plastic oil tube connectors, and you'll be good to go.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

my 420sel is pretty slow by todays standard for sure, but I do say it feels faster than it is. It can hang with some of those japanese imports though.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual