I ended my 400 mile trip yesterday with the trip computer showing an average of 27.1 mpg. This was after crusing at 80 mph most of the way.

That just seems unreal from a car with a fat engine. Is the computer gassing me or what?

Is yours a 55? I usually get 22mpg on highway in my cls55.

last year i did a trip to chicago and back and got an average of 23.5 mpg , most of the trip i was 80-85 mph and cruise only part way......

Mine's a 2000 E55. 27 mpg just seems unreal.

Upon a further 300 miles this weekend, I am consistently showing 23-25 mpg highway. Is this for real?

At one point when my car was screwed up the trip computer was telling me 21mpg-in the city! Insane. It's a much better 14 now.

According to some tests, you should be at 16/23 mpg. You can try the old method and fill the tank reset odometer. When you refill the divide miles with the gas you put in. (sorry if you already know that).

Yes, the trip computer is wrong. I did the old fashioned mileage count divided by gallons filled between 2 identical fill ups yesterday and only got 22.xx while the trip computer was showing 25.2.

This is still heartening because I was caning it. I briefly hit 130 mph when I was playing cat and mouse with a BMW 540i on the highway. With that much abuse, 22.xx for a big V8 is decent.