I doubted that the 2009 e320 bluetec could get over 39 mph. I slowed down to 60 to 70 mph and got over 40 mpg, air conditioner turned off. Tires at 40 (f) and 44 (r), Mobil ESP 5W-30

 

That's only for a moment in time. My Bluetec mpg with low profile tires and some crazy daily highway driving is down to an average 27mpg. I know I can get 32-35mpg average if I drive normally but prefer to have fun with the car; I'm happy with my 26mpg.

 

Normal City driving is 24 mpg, combined 28-32 mpg, normal hwy 35-36 mpg (75 to 80 mph in one lane to keep up with the flow of traffic).

I would be a hazard on the road if I went 60 mph and would likely get rear ended.

I've not tested if Comfort or Sport mode on the 7G tranny makes a difference in mpg. There's a lag in highway acceleration in the C mode.

 

I have a 2005 CDI. There is no change in MPG while coasting along around 80mph. Both netted us 37mpg on 70 E to Baltimore on Friday around 6am.