There is no way a M103 will do 20MPG routinely in a W126. No way no way. My W124 with a M103 averaged 16-17Mpg doing mostly city miles, and that was a lighter, more aerodynamic car. And that was when the engine WAS running well, which it often was not....when not it was more like 12-14mpg. My 420 averages about 18-19 city if driven gently, 15 or so driven like a maniac, and about 23 highway on cruise at 75mph with no A/C....about 21-22mpg with A/C.

It seems like the Ignition and CIS on the M102/M103 is much more finicky than on the M116/M117 engines too.

The small old gassers aren't worth the trouble, not enough power and bad fuel economy. The V8's and diesels are much more fun. The only smaller gasser I am a fan of so far is the M112 V6...its a beast. Mine has 132k on it and is bone dry and runs beautifully. Far superior to the M102/M103.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I get 21 mpg in my 300e and I kiss the redline every day. Road trips have netted me nearly 26mpg. My 300te 4matic runs like pure crap and I still get 14 mpg.

I won't deny that v8's are much more fun.

When I owned my 300se I averaged 20 mpg, seeing as high as 22, and low of about 17. You should bring your m103 over sometime so I can get it to run right for you.

__________________
Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

These numbers sound right to me. The 3L m103 in my 190E was getting me 24-25 mpg on the turnpike doing 70-75.

The 420SEL does 20mpg at 70-75mph.

I drove the 560SEL home from NYC and it averaged about 21-22 on the freeway.

__________________
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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

I have a '91 300SE with 97K miles on it and I love it. It has been 100% reliable. I bought it from a friend 4 years ago who had it since 30K miles, and it was 100% reliable for him too.

I do my own maintenance and recently (at 90K) did a full tune up and it was a true pleasure to work on. Other experiences vary, apparently, but my M103 runs perfectly. I have a pretty good knowledge of CIS engines and did have to tweak the base fuel mixture a couple years ago to get it running smoothly again. So you may have to know a little about CIS engines, or know somebody who does, to have it run smoothly. But there are a bazillion M103's out there with good forum posts on diagnosing and repairing every aspect.

Power is not too bad, and I have owned a 560SEL and so can compare directly the W126 6's with the 8's. I agree it isn't the greatest on the highway, it really needs and overdrive! But around town, where I do most of my driving, it's actually just about perfect with it's short gearing and rear end ratio. You just need to have a slightly different philosophy when driving it and not expect too much. I just sort of "ease" around town, and the engine is buttery smooth and quiet. As long as you don't ask too much of it, or think it should drive like a sports car, then it will give you a great around town driving experience.

The short wheel base make a surprisingly BIG difference in the way the car handles even around town. The short wheel base W126 isn't exactly a sports car, far from it, but it isn't bad. Decent turning radius, and the whole car feels simple and robust. The long wheel base "L"'s are just huge boats in comparison. Don't know why it makes such a big perceived difference, but it does. I like the 300SE a LOT and the short wheel base has a lot to do with it.

Overall, I think the M103-powered W126 300SE is a great car, especially around town, not so much on the highway. It's the mating of two classic Mercedes designs: the W126 with the M103.

Oh, and I get 17-18 mpg in town and 21-22 on the highway.

__________________
1972 280SE 4.5
1984 300SD, 250K
1991 300SE, 89K
1992 300D (330K miles when KIA'd by mother-in-law 8/10/09 - still sitting in my barn)
1994 E320, 109K
1995 E420, 60K
Proud Member of the Mercedes Benz Club of America - Idaho Chapter

^^^

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

The 240D is a 3.69. I think the M103 is a 3.46, same as the 300D NA.

__________________
"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Yeah that's way too high, 4k rpm at 70ish mph on the freeway is ridiculous. It would work much better if the transmission had been a 5 speed or had overdrive.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)