I6. When we get the new I6, our mpg should go up too, but that's not for at least another year.

Has anyone tested out what the optimal speed is in top gear for the best mileage? Is it around the 55mph mark or the 90mph mark for example? I suppose this could be done by setting the cruise at various speeds on a nice, long, straight highway with little traffic and resetting the MPG calculation at various speeds. Sounds like a fun task. I'll try it some time when I get a chance, but if anyone would like to beat me to it, it would make for an interesting read...

And one more note, when you're stopped and idling, why does the MPG gauge on the dash read max MPG when it should read min MPG? If you're not going anywhere with the engine running, you are getting 0 miles to the gallon. I'm assuming it's because the gauge runs off engine vacuum and it's just not that sophisticated...

Physics tells you that to move X amount of weight to Y velocity requires Z amount of work. The 6 and 8 will use the same amount of energy to propel the vehicle (assume same weight) to the same speeds.
I believe the fuel savings on the v8 might be from the 6th speed gear ratio, it probably runs at a lower RPM at an equivalent speed than that of the 6 while in 5th gear.

For me, I never use the cruise. I feather the peddle lightly going down hill to pick up speed, then ease off the pedal going up hill which brings me back to my original speed. I cruise at about 75mph. Thats the best for my car.

The 4.4 is a newer design than the 3.0 which incorporate new, more efficient technologies, like valvetronic. The 3.0 is a much older design which is being replaced(new 3 and 5 have it) but not on the x5 yet. And by the way, the 3.0 is not a V6 but an inline 6.

I have a 4.4 and you will pay dearly for the gas!

it will be if Rita hits the Texas coast..

I have a 2005 4.4, and I don't care what you drive...if you have a heavy foot around town you will pay!

I usually pull off around 16 MPG in town, but this thing is great on the highway. I am getting 26 MPG by driving steady around 60 mph...and this thing isn't even broken in yet.

I once read that the optimal speed for gas mileage in cars was 47.something... I imagine that it would vary depending on several factors (C of Drag, mass, etc.) but it's probably in that neighborhood for all vehicles. :confused:

Assuming that instantaneous fuel economy gauge on the cluster is relatively accurate, you should be able to figure it out fairly quickly. Start at 40 mph on a flat stretch (cruise control on), and increase in 5 mph increments while checking approximate fuel economy. You'll probably find a sweet spot...I'm going to try next time.

My 2001 4.4i averaged .5 mpg better than my 2001 3.0i. I suspect that my 4.6is will not do better...because it will be way too much fun to drive at full throttle.