MPG will get BETTER at altitude
 

While the thinner air may be less drag on the body, that thinner air is also registered by the motor and less fuel is delivered. I find my AT '92 300E 3.0 to be overpowered/overgeared at highway speeds at 600 feet above SL. With a bit more tuning still to be done, I just saw 22 MPG combined. EPA was 16/20 or so.

Can you guys list motor size, tranny type, altitude and if you are using 128 oz gallons or 154 US oz / 160 UK oz gallons when giving MPG numbers?

Also, what tranny and diff options do we have on the 3.0 M103 / W124?

Yes Jim. I figure there's probably some compensating factors that cancel out whatever "advantage" the smaller displacement has over the 3.0L, like lower gearing (3.27 vs. 3.07 rear end). Anyway, when compared with the EPA rating of 18/22, I'm satisfied with its performance at the moment, and that's with 207,000 miles on the car.

The mileage stats I reported in my first post above, were about two-thirds flatland freeway driving, and one-third hilly country, some of it up to 3,200 ft elevation. New tires, new O2 sensor, new distributor cap/rotor and new ignition wires during that time. Plugs replaced 12,000 miles (2 yrs) ago.

^^^^
Keeping the engine well maintained pays for itself in FE.

Here are my numbers from the GPS on one of my trips. I make this trip all the time (15-20 times a year) and routinely see numbers right around 30 - this is just one example where I tracked the heck out of it. I haven't crawled underneath the car and checked the diff stamping nor have I verified the transmission. My car is a theft recovery with the speedo/odo off so its very possible I have a weird funky gearing in there which translates to better mpgs.

207 miles, GPS tracked, not odometer
Average temp 72*F (started at 77, ended at 67)
Distance measured gas station to gas station, volume measured by when the gas comes up to the brim of the fiiller neck (visual)
Gas to fill up: 6.753 gallons
207 miles / 6.753 = 30.65 MPG.

More variables:
Average temp 72*F (started at 77, ended at 67)
Total ascent: 1,538 ft
Total descent: 1,546 ft
Average speed: 61.2 mph (really good since I hit a lot of construction)
Max speed: 78.2 mph
Total time: 3:22 and 36 seconds
Humidity 81% (hit fog on the way so this varied quite a bit)
No A/C, just econ mode on the low fan setting the whole way
lights on the whole time, fogs on most of the time
Fuel was 10% ethanol (noted this)

anyone try using fuelly to keep track of their mileage?

http://www.fuelly.com/driver/biking4jesus/300e

ive only just started keeping track of FE in the benz, as the ODO wasnt working (worm drive gear issue) and has since been repaired. i just changed the oil and thermostat so hopefully the next take i get better results. 80% city driving, which sucks here in san francisco.

The real issue is...
 

"What wheels are worth a 400 mile round trip?" :)

Pics, please.

Somebody been sneaking around at night and adding gas to your tank!!!

Years ago, we actually pulled that old trick on a friend who bragged so much about his V-Dub's gas mileage. We added a little bit to his tank for a couple weeks in a row; and he was really proud of the MPG. Then, we siphoned a little out for the next couple weeks - drove him crazy.
Wasn't college fun, so much time, so little to do.

My big ol' 300SE with the 3.45 diff will get about 18 MPG on the highway doing 70, and about 18 around town. And about 18 sitting in the garage, it seems. Sigh.

Average speed is crucial. I drove the 190e 2.6 manual from seattle to the bay area last friday. First tank average speed was 68mph, burned 12.7 gallons to go 397 miles, 31mpg. Second tank I had to use AC through california, average speed was 70mph, 28.8mpg. Both tanks involved some mountain driving over the Siskiyou pass. I always use 87 octane with the R16 resistor removed.

just took a 140 mile RT on saturday in the 300E. ended up getting about 26mpg, cruising at 70. i figure if i do a tune up (new plugs, wires and dist) it might help account for another 1-2mpg.

tire pressure also can play a factor, the tires were around 27psi to keep the ride plush, but bumped them up to 32 and it definitely rolls further/longer.

i also put in a bottle of techron w/ the last tank, so we'll see if anythign improves otherwise.

city driving yields 15-18mpg.