No, 50Mpg is not remotely possible in a 2.2 NA 190d, if you really try you can get upper 30's.
The W201 is way better than the W123. Its smaller, but handing, ride, climate controls, accessories, seats...all of it is better.
With the 2.2 601 engine its also super easy to work on.
With the auto trans, om601 in tip top condition, and 2.85 differential, I get about 26-29mpg city, and up to 35ish on the highway.
With the auto and tall differential its SLOW however. 0-60 on flat ground and good conditions is MAYBE 19 seconds or so...I'm sure my 420SEL can top 100mph before the 190 can hit 45
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