eddieo45

I have the 3.5l six in both cars. we just took the E350 away on vacation, and on the way back, 60 traffic-free highway miles, I think I got about 23 MPG. I just took my CLK350 down to the cape, a round trip of mostly traffic-free highway driving and got 29.6 MPG over 140 miles, and I was seeing 30.0 before hitting the little bit of traffic, then the standstill that is my home town. Same engine, very different economy.

werewolf34

I think the 4matic accounts for some of the difference

eddieo45

big difference though.

Vik888

If those were truly highway miles, that is very low.

I've done quite a bit of highway only driving in my 08 E550 and I can hit 27mpg avging around 65mph.

Xander Crews

How fast were you going during each of the two runs? If much over 65 MPH, you're going to see a quick drop off in MPG. A friend gets around 25 MPG at ~65 MPH in their E350 4Matic.

eddieo45

That might be it. I think I was closer to 75-80 with the E (in a hurry on a vaca day) and more like 65 in the CLK (no hurry on a blow off work day).

Xander Crews

Yup. My diesel, which should get 34+ MPG on the highway, only gets ~32 MPG at 75-80 MPH.

dynomite05

They say 60-65 mph is optimal driving. Driving down to FL a couple months ago confirmed this. Whenever I would speed up to 70-75 the mpg would go down. They also say using your AC at this speed (60-65) wastes less gas than having the windows open.

brwnskin2789

at speeds over 60 mph fuel economy drops 33%

lkchris

Aero drag increases with the square of speed.

LaicepsYdobon

Also don't forget the weight difference between the two cars.

gaazmon

it's the 4matic