Hello,

I have an '86 300SDL and am experiencing lower fuel economy than others (I think).

I get approximately 21mpg in combined city/highway driving. Just completed a trip of 480 miles (all highway) and got 24.9mpg.

I'm driving between 75-85mph on the highway and the A/C was on but it was only 75 degrees outside (so the A/C shouldn't have been too much of a load).

How come everyone else is getting 30mpg and I have even heard of 35mpg when driven all highway?

Is there something I can check to figure out why I'm getting 10mpg less than everyone else with the same car?

Here's some vital info:
-Both fuel filters changed yearly (about every 18-20,000 miles)
-Car is in proper operating condition
-ALDA adjustment screw was loosened, but only 1/4 turn. Didn't affect fuel economy at all when I did it.
-Filling tank each time to same point -- fill until pump shuts off, then top off slowly until the filler neck is completely full.
-Brakes have been replaced multiple times since I have owned the car, parking brake has been checked to make sure it isn't dragging. No effects on fuel economy before or after brake jobs
-Tires inflated to MB specified pressures as marked on fuel door.
-Using Michelin MXV4+ tires in summer, Pirelli Snowsport 210 in winter (stock size for both sets). No noticeable change in fuel economy between winter/summer tires.

Thanks for any help you can give me!

Neal

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'83 300SD 335,000km (207k) mi SOLD
'87 560SL 163,000km (101k mi) SOLD
'86 300SDL 356,000km (220k mi) SOLD
'92 500SEL 250,000km (155k mi) SOLD
'90 300SL 140,000km (87k mi) SOLD
'01 S430 260,000km (161k mi) SOLD
'03 SL500 167,000km (104k mi) SOLD
'07 S550 4MATIC 235,000km (146k mi) SOLD
'07 GL320 CDI 4MATIC 348,000km (215k mi)
'13 GL350 BlueTec 4MATIC 170,000km (105k mi)
'14 SL550 72,000km (43k mi)

Highway speeds with A/C on a good day will touch 29 mpg. Combined intra-city and highway 27 mpg on an 86SDL with 220K.
BUT....driving style seems to dictate my biggest drops in mpg. If I am keeping the toenails in the firewall, flooring it, etc - it will set down in the low 20's easily.

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