I'd drive slower but I've got things to see and people to do.

We had a thread about this in one of the other car forums (can't recall which) awhile back.

Contrary as it may seem to some people, some cars get optimum highway mileage at higher speeds. My LS460 is like that, and so were my BMW's - 540i's and 740i. It's all a function of the balance between coefficient of drag, engine rpms, ECU "tuning", gearing, etc., but it is true.

On a recent 3500-mile trip in the LS, I was getting 29-30 at 80 on the interstate, but when we went to a secondary highway across 400 miles of Nevada at an average of 60-65 mph, my mileage dropped to about 27. Back on the interstate, it went back to the high 20's and low-30's. It wasn't a matter of hills or traffic (hey, this was the Nevada desert!), so I can only assume the car is just optimized for more speed.

I had the same kind of experience with my Beemers, too. The best mileage I ever saw in the 740i was blasting across Montana back when there was no posted speed limit. Ran 90+ across there, and my autobahn runner turned in the 28's. Sweet.

I suspect the higher revs and sporty nature of the M work against it in high-speed running, because my M45 was like that, too.

Mike

At 90-100 steady I get about 15-16MPG

I guess that's one of the few good things about florida.. you can get relatively balanced gas mileage on the interstate if you try. 95% of the state is completely flat. Really, really flat. Flat. Did I mention it's flat?

PS.. you have an M35.. the gas mileage isnt THAT bad in that!

12mpg?!

Are you pulling a trailer? I think I get about 14-16 city, but again.. extreme flatness. Are you somewhere hilly/mountainous (is that a word?)

Wenatchee isn't totally flat-there are some hills, but its not mountainous (it is a word!). Yeah, 12mpg on a good day. Tell me about it. Hell, I don't complain-I didn't buy it for the mpg. An M45 would have been overkill. I've driven 4 and 6 bangers all my life. Back in the '70's I drove an 80hp Saab 99E and had more fun in it than you can imagine. Of course I was also 30 odd years younger, and a lot more limber...

Stopping and starting every block and running up and down the hills here in San Francisco, I get 14.5 consistently.
Coincidentally when I drove down to LA and average 90+ I got the same fuel economy.