Is there some sort of difference between the 92/93 300SD and the 94/95 S350 that would cause a higher MPG rating? The 300SD is rated at 22 highway and the S350 is 26. Do the later cars have a different rear end gearing ratio?

Unsure about the Diff ratio, but I Believe in 1995, the 5spd auto replaced the old 4spd unit

The 95 diesel still used the 4 speed.

I'm not aware of the W140 603.971 cars having different differential ratios. I think it's even the same as the W126 350SD/L.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

What year did the w140 get the om606? I’m sure that has an effect.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

The 140 never got the 140 in the US