I've got a beautiful 1975 230 Sedan -- W115 chassis, 4 cylinder gas. 64k original miles, near perfect shape, runs beautifully, I use it everyday and LOVE it -- except the gas mileage is HORRENDOUS! I'm lucky if I get 15 mpg on a tank, but with a lot of stop-n-go 'round town it's more like 12 I know it's a small, low-powered engine (93 hp) in a heavy car (3,000+ lbs), and it's not a diesel -- but surely I should get a bit better mileage than that? My questions:

1. Is this normal?
2. If not, any suggestions on how to improve matters?

It just recently had a tune-up.

Thanks!

If it starts and runs well and the spark plugs are light tan or light grey it probably is running correctly and that may well be all it will do. Is it an automatic?

If it were a stick I would expect it to get over 20 highway, but an automatic would do less. Have you checked to see that there are no brakes dragging?

Tom W

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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.

Hmm, if averaging 15 for entire tank and gettin an estimated 12 in town - then ye must be seein 18mpg or better on the highway sounds probly normal to me. By comparison my 4-spd 190c 4-cyl fintail (pitifully underpowered with 20% less displacement than yer 230) generally averaged 19mpg per tank or 23 at best on highway with lows somewhere at/near 15.

Quick trick that can help ye git better mileage is *over-inflate* the tires. If they recommend 32 lbs - try 38 instaed.



.

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'80 300SD/ w116
'79 240D 4-spd
'71 750cc Guzzi

previously owned:

'83 240D 4-spd
'77 280SEL 4-spd
'74 280/8
'72 250/8
'65 220Sb 4-spd
'63 220Sb 4-spd
'63 190c 4-spd
'61 220Sb 4-spd
'60 190b 4-spd

Assuming you've checked all the usual suspects - tire pressure, fuel leaks, dragging brakes, trunk full of junk, tranny performance - there are other things you need to look at.
Many years ago, I bought a '72 220, 4-cylinder with automatic. On my first highway trip it got 11 mpg! Turned out the mixture screw (combined with the idle fuel cut-off solenoid on the bottom of the side-draft Stromberg carburetor) was adjusted way too rich. Sometimes, mechanics will adjust these for max power, without a CO meter or regard for gas mileage. Leaning my adjustment slightly (a partial turn makes a big differnce on these Strombergs) upped my mileage to about 14-15 city and 20-23 highway. Don't lean it too far, as the mixture screw adusts the whole operating range not just the idle mixture. Another trick that can improve performance and fuel mileage on these old cars is to advance the ignition timing slighly. Up to 5 degrees is possible, but listen carefully for pinging, which will be more likely during hot weather. You may then have to back off timing a bit.
Happy Motoring, Mark

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DrDKW

...at the expense of ride comfort and decreased braking performance.

Here are some mileage specs of the most economical old gas benzes straight from the horse's mouth, converted to mpg: (it was a really slow day at work)

[w110-m121]
20.5mpg 80hp@5000 93.2mph 1.9L 85x83.6mm 1xSolex 2822lbs man "190" Apr 1961
18.8mpg 80hp@5000 90.1mph 1.9L 85x83.6mm 1xSolex 2910lbs auto "190" Apr 1961
18.8mpg 95hp@5200 100mph 2.0L 87x83.6mm 2xSolex 2888lbs man "200" Jul 1965
17.4mpg 95hp@5200 98.2mph 2.0L 87x83.6mm 2xSolex 2976lbs auto "200" Jul 1965

[w115-m115]
21.6mpg 156Nm@2800 95PS@4800 99.4mph 2.0L 87x83.6mm 9:1 1xStrombergCD 2921lbs "200" Jun 1970
21.2mpg 179Nm@2800 105PS@4800 104.4mph 2.2L 87x92.4mm 9:1 1xStrombergCD 2921lbs "220" Jun 1970
20.6mpg 186Nm@2500 110PS@4800 105.6mph 2.3L 93.8x72.8mm 9:1 1xStrombergCD 2976lbs "230.4" Jun 1973

[w114-m180]
21.0mpg 179Nm@3600 120PS@5400 108.7mph 2.3L 81.75x72.8mm 9:1 2xZenith 2987lbs "230.6" Nov 1972

[w114-m114]
20.1mpg 200Nm@3200 130PS@5400 111.9mph 2.5L 82x78.8mm 9:1 2xZenith 3031lbs "250" Jun 1970
20.1mpg 200Nm@3200 130PS@5400 111.9mph 2.5L 82x78.8mm 9:1 2xZenith 2998lbs "250C" Nov 1971
20.1mpg 216Nm@4500 150PS@5500 118.1mph 2.5L 82x78.8mm 9.5:1 D-jet 3042lbs "250CE" Nov 1971

[w111-m180/m127]
18.1mpg 120hp@4800 105.6mph 2.2L 80x72.8mm MFI man "220SEb cpe" Sep 1961
16.8mpg 95hp@4800 99.4mph 2.2L 80x72.8mm 2xSolex man "220b" Aug 1959

This is from M-B literature, but with no regards to highway vs city and so forth. I don't think there was such a concept back in the 60's when most of these were stated. Most likely they are best possible mpg measured under ideal conditions. Even still, yours sounds pretty low for that chassis/engine combo.

I put in top speed, but not accel. You can derive low end grunt from the torque spec, although I only have it for the later cars. If anybody has factory torque specs for the 60's cars I'd be interested in comparing them. The figures which seem the most suspect to me are the m114 mileage ones, I can't believe that they got that much more performance and didn't effect mileage at all with no increase in CR and rising weight/disp. I doubt they all got 20mpg, the others figures do seem to make sense though.

I have the bigger sixes and V8's too if anyone's interested, but they are pretty scary! (mostly in the 12's to 13's)

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1967 230S automatic
Boston, MA

My wife's '72 250C, manual trans, M115 dual Solex carbureted engine gets about 18 mpg in town with me driving and about 15 mpg with her driving. She has a lot more fun driving it than I do.

We both get about 20 mpg on the highway. She turns into a "grandma" once she hits the interstate. I start looking for flying goggles and a leather cap when I hit the open road.

Thanks to all who have provided feedback. My brakes are great, I don't have too much junk in the trunk, it starts and runs great -- so I must be right where I should be. So much for the gas saving qualities of the 4 cylinder engine! I know, it was the emission-strangled 70s and the car is made the way M-Bs used to be made -- carved from a steel block. And fuel economy wasn't even a consideration when I bought it. But I must say, as a daily driver getting 12 mpg and costing $60+ to fill up (premium is over $4 in Washington state) -- it's starting to sting. But man, these W114/115's are mighty sweet cars!

Thanks again!

I gladly stand corrected. In that case the w114-m114 combo seems to be a really good mileage/performance compromise. 20mpg hwy is pretty darn reasonable for an early 70's six!

I still think 12 is really low for a 4-cyl, regardless of city or hwy.

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1967 230S automatic
Boston, MA

My recently departed W114 M180 230.6 (see Otto thread above) returned 19-20mpg on my short work commute of 5miles each way, and upto 23mpg on a long run. It was the model with twin Zeniths. 15mpg from a 4pot does seem thirsty for sure!
edit- my W114 is a 4speed manual

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'82 W123 280E

I suspect 99% of the '75 230s all came with automatic trans. That plus the 2.65 gearing in the differential makes for relatively poor mileage.
I have a 220 with the '75 engine the same as yours but I installed a Weber carb. Its a stick shift and I replaced the diff with a 3.07 gearing and its barely able to get 20 MPG at 55 MPH. It will however cruise well at 70 which my 230.4 wouldn't without having the engine revved all the way up.
Basically the carbureted gas engines weren't designed for fuel efficiency.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

It is an automatic -- I don't think you could get a manual withe the gas engine in the states in 75. And at 70-75, it is revving up to high heaven -- like it should shift into a higher gear. It seems this is all normal behavior. I hate sounding so ignorant, but this is the first 4 cyl M-B I've had -- we had sixes and eights in the family while growing up, I had a 280C about 15 years ago, and more recently an 87 300TD.

Well, pretty soon it will be Summer in Seattle and I can start riding my Vespa to work (50-60 mpg).

Thank you!

Jeff

A stick swap and a higher rear end ratio would probably put you into the twenties highway. The parts should be fairly cheap if you can find them. The labor is not too difficult either.

Tom W

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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.

My '72 automatic 220 definitely got better than 12 mpg once I did the previously-mentioned carb and timing adjustments.
Note - After '71 these 4 cylinders had reduced compression to allow use of unleaded regular gas, so a '74 shouldn't normally require premium.
Also, when I replaced my '72 220 with a nearly-identical, similarly-tuned 6-cylinder '72 250, my gas-mileage only dropped by around 1 mpg.

Happy Motoring, Mark

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DrDKW

I have a '73 220 with a 115.951 motor out of a '74 230 in it. I run the 'mid grade' gas in it and it gets 16 mpg in stop/go 'in town' driving and it gets pretty much 25 mpg on freeway driving at 65-75 mph. This has been very consistent for years.

One thing I changed years back that definitely improved the fuel economy was to change the needle in the Stromberg carb (a 175 CDTS). I changed the needle because I was having problems getting it to pass smog (HC emissions). We had already squeaked the car thru smog testing with some strategically placed staple clips on some of the air diaphragm spring coils to change the spring constant and lean it out at speed, but I ordered the needle anyway.

When the needle came in, I swapped it out, removed the staple tweaks on the air diaphragm spring and we re-adjusted the mixture to 1.5% CO per the standard manual method, and VOILLA, the measured HC values dropped to one fifth of what they were before the needle swap!

In examining the old & new needles, the first thing I noted was that unlike the SU predecessor, the Stromberg has the needle cocked off to one side (off axis) by a spring. This causes the needle to rub on the needle seat on that one side. This caused abrasion wear on the needle, which thus changed the mixture profile vs airflow thru the venturri.

The other interesting thing about the needle is that the cross-sectional profile is NOT a linear taper, but a non-linear profile; it even appears to have a non-constant curvature, so there was definitely some painful empirical tuning to derive that profile.

If your needle hasn't been changed in a long long time, then I think you'll probably find the same condition and very small changes in that profile have a very large effect on mixture.