http://www.mpgfacts.com/?r=g&make=Mercedes-Benz&year=1984

Heres some research Ive done with this site .
Comparing a Mercedes 1984 190d 2.2 5spd to the current market of High Effciency cars available on this site .
1st place Toyota Prius 50 MPG combined Hwy & City
2nd place Honda Civic Hybrid 42 MPG comb
3rd place Ford Fusion 39 MPG comb
and tied for fourth is the Smart and the 190d at 36 MPG combined

Ill be attempting to hurtle the 50 combined mpg hurtle hopefully with some tuneup tricks and a lighter load to carry .Im currently waiting on an injector socket to fix the leaking IP and I have a fresh set of tires on a set of 240 aluminium rims.If I compare the 190d to a non hybrid car then the ford is the one to beat . Ill give some new updates soon.

Without trying at all(and low compression) I got 45 mpg out of my old '85 vw golf diesel 5 spd, wow a mouth full. But it was like 48 or 58 hp. I know it has nothing to do with the OPs question but i thought I would share that high mileage can be done with an old diesel.

My old '85 190d 5 spd parts car got very good mileage but the odometer didn't work... but you could really tell it did well in the mpg department. My '85 TD get's 22 mpg on the highway with a/c on and alda removed.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

The numbers for the 300D look about right. Notice that the W201 was a "subcompact" and the W123 was a "compact." The W126 was "midsize."

and the 617 turbo got the same in the 123 and the 126 bodies.

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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.

And where is the current Golf TDi in your mix? 45mpg all day in a Golf/Jetta TDi. You'll never see a Prius or a Civic in our driveway !

I am very interested in your pursuit of higher mpg in a benz. Keep in mind that getting more cool air INTO the motor and getting the HOT exhaust OUT as efficiently as possible are also important.

Consider water/methanol injection (very simple), and modified exhaust to achieve both. Turbo charged motors are always more efficient than non-turbos. The civic and prius would get better mileage with forced induction.

Keep us updated.

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.

If we are looking at high MPG vehicles, do not forget the 2000 - 2006 Honda Insight hybrid. I belive this is still the highest rated MPG production car in the USA. My 2000 Insight with 90000mi has a liftime average of 63.4 MPG.
My 190D with 251000mi is not even close but I am sure will last longer.

I love the uncompromising design of those old insights.

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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.

On the site ,if you want to see and compare all compacts you just click the word "compact".
I bought the 2 190s last month from a man who drove a tdi ,we took a spin after he helped me get the cars home ,thats a real nice driving car with plenty of power.
Its Intersting that the 5spd makes the automatic car feel like a slug and will get the most driving no doubt .Ill make an effort to bring both cars into this contest.

New updates ,Im now driving the 5 spd and its performing well .Put some euro lights on and shes looking like a new car.Ill be driving it for a week to see what the city mileage comes out to ,then its on to the highway for a day .Ill make some mods then try for some new numbers the week AFTER.I really like this little MB.

Heres the updates ,33 city and 45 hwy ,thats better numbers than the 30 city they report but less on the hwy side by 1 mpg .I stayed around 65 mph and had a nice level stretch of hwy.Im going to do more post thru the month of sept and have some pics of the car here soon.

I'm guessing if I drove my old Honda Accord into the mid 80s they would say it is a μcompact car

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-Typos courtesy of my mobile phone.

It might be doing it the hard way but way back in the 70s Automakers they said that if they eliminated 400 pounds of weight from a car there was a 1 mpg increase in the milage. But, this was concerning Gasoline vehicles.

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84 300D, 82 Volvo 244Gl Diesel

Weight will effect things when stopping and starting is involved. On the highway it has little effect....possibly increasing steady speed driving by lowing the car for better aero!

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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.