My normal average is 26mpg city/highway. On a recent 525 mile trip to Cleveland and back cruising at about 75mph, I was approaching 28mpg but Brian is right above 70mph the mileage suffers. Car has 192,000 miles and only smokes a bit at start-up from cold and when I really boot the throttle.

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown

Best mileage, all highway, was 28MPG. Lowest, all city, was 22MPG. I usually see 23-25 MPG. I'm hoping for a slight improvement with my new air filter and disconnected EGR. I have not used any fuel additives.
Dave

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1986 300SDL

The W126 must be significantly less aerodynamic than the W124. I see *very* little change in MPG whether I'm cruising at 70mph or 90mph, it usually hangs around the 29-30 range. My 'peak' MPG (31-32) has been when I'm driving the car to work daily, 16 miles one way, several stop lights, and mostly 40-55mph plus one or two short freeway trips (~60 miles round trip) at 70-75mph on the same tank. My record so far is 515 miles before the reserve light triggers and fill up at 575 miles. Next year I'm shooting for 600! :p I'd love to see if the MPG drops with steady 100 or 110mph cruising but since Montana resurrected their speed limits a few years back, I can't really do that...

My poor beast comes in around 22-24 for my combined trip cycle. I have replaced the airfilter and "discovered" a blockage in the vacumm line to the EGR. Rest of tweaking will have to wait. Did fix the odometer the other night. We'll see if it quits again when it tries to turn the next 10k mark.
I up for a trip to NY. Little far, but it'll be a trip for someone no matter where it is held. Besides, I'm way behind on the run to 250k miles and I gotta catch up.
oh yeah: '86 300SDL 220,345 miles

If you think you are getting low milage, I would check the following things (in order)

Dragging brakes -- rear especially are very difficult to "feel" and will eat up fuel. By now, it's time to think of caliper rebuilds all round anyway, the rubber is getting pretty hard after 18 or so years.

Timing chain stretch/injection timing. The 603 starts pretty easy all the time, unlike the 61x engines, were late timing will make them impossible to start in the winter, but it will still kill the power and milage.

Font alignment. Poor alignment is good for at least a couple mpg, and eats tires, too.

Low boost on the turbo -- you spend more time with your foot down. Not so bad most of the time.

Miss-adjusted ALDA --too rich. My friend Hans bought a charity car, 84 300D, I think -- ALDA was set too rich, had tons of power but barely broke 20 mpg on the highway. Reset the ALDA leaner, power returned to normal (no more runaways on hills!) and milage jumped to around 26.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

86 SDL here. 152K miles. Synthetic oil. Only run it June through November. Average 23.7 MPG like clockwork. Worst about 21, best 27, haven't been able to replicate that. Don't know if my EGR is connected or not.
Like the idea of a get together in NY next spring. Let me know.

BTW, where in NY? I have family in Rochester and just north of NYC.

I would consider hosting a DC version of a get together sometime in the spring.

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Alan Hamm
'87 300SDL 277K Miles
'89 560 SL 68K Miles

Folks,

I'm averaging mid-20's. Down to 22 in the summer, AC all the time, and was in hi-way to stop and go. I just went to Charleston SC and back, 70-75 mph, no AC and got 28. Most of the time in my current short commute of 10 miles suburban driving I am getting 24-25. Just crossed 270K, original timing chain, ALDA, and head/valves/injectors.

Let me know about an "SDL" get together. I'm from Western NY, and DC is not far from NC.

Chuck

I was averaging 20 mpg with a bad head. Since then, I've replaced the entire top half of the engine, and adjusted the ALDA for performance. It is accelerating great with little smoke. I havn't run a new tank through, but I am hoping for mid 20s like many of you are getting. I plan on adjusting the ALDA to maximize performance and fuel economy. I would love to see high 20s like GSXR.

I have seen, I know I've posted this before unless I'm going mad, 32 mpg at best. This was the one tank I drove with a light foot and mostly rural roads at average speeds of 40 - 45 mph. Maybe 10 full stops in 15 mile distances. Last summer was worst on record. I averaged a lousy 27 mpg. Terrible fuel economy. It used to be that in winter, the worst I could EVER get was 26 mpg, no matter the temp or my driving style. FWIW the 350SD and 300SDL go hand in hand in regards to overall economical efficiency.

The W126 pre '86 was 0.36Cd. The W124 was super sleek with aerodynamics as low as 0.30Cd. I think the 126 post '85 is quite a bit more aerodynamic than the earlier versions(no square headlamps, encapsulation panels, lower side skirts, flat faced 15" wheels, just to name a few differences). But they still have those HUGE '70's polyurethane coated bumpers which may help reduce the cost of a collision, but also don't help with complementing wind resistance.

Per the 1987 sales brochure, the 300SDL has a CD of 0.37, same as the 420SEL. Oddly, the 500SEL is 0.36. The 560SEC coupe is 0.35. The 560SL roadster is an awful 0.43.

There you go, Dave. I suppose those mostrosities(bumpers) keep the Cd from being stellar. The 500SEL(did you mean 560SEL?) was more aerodynamic. However, that doesn't make sense as it has EXACTLY the same proportions as the 420 and 300.

You have the original sales brochure, Dave? Can you host it online so that I may see it? Sounds like there is a LOT of interesting information in that brochure. Thanks.

BTW, the Cd of the new SLR is the same as the SDL. 0.37. Interesting that even in today's world the ole' W126 is still as serodynamic as the exotic supercars of today.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

I believe the reason the 560SEL was more aerodynamic because it sat lower with the pneumatic suspension. Also if you read the spec's it also states the 560SEL wheelbase is 1" shorter. The body is the same, but the pneumatic suspension setup caused the 1" offset.

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Mercedes Fleet:
2004 CL600 Designo Espresso SPORT
2004 S600 Designo Espresso SPORT/Lorinser Pkg.
1999 S320
1988 300TE
1972 280SEL 4.5
Diesel Fleet:
2014 GL350 Blutec
1987 300SDL Blk/Blk 4 place seating #18 head
1987 300SDL Smk Slv/Burgangy #17 head
1986 300SDL Blk Pearl/Palomino #14 head w/ 280K
1984 Lincoln Mark VII Fact BMW Turbo Diesel

Since we resurrected this thread, I'll just let everybody know that the winter fuel has dropped my fuel economy from 29.5 to about 26.5. No changes to driving style or road conditions. The change was immediate and apparent in mid November. I found the same thing with the SD last year. I dropped from 27.5 down to about 24 for the all of the cold months.