Mileage would be the least of your worrys if you see mine on a lot when the lease is up. I don't drive it much but when I do, its typically destined to go off road before it goes back into the garage. If it's on the lot after the lease, its because I abused it more then I would want to own.

 

I have about 8k miles on mine now - 15+ in the city and 16+ on the highway. 33" tires.

 

I have never got less than 16.8 mpg. I do see 20 at steady highway driving. Last tank full just averaged 18 mpg with mixed city/highway. Using Mobil 1 synthetic might help me get another 1 mpg. I do drive non-aggressively in the H3 but make-up for it in the Z06. Ironically, the Z06 gets much better gas mileage at 17 around town and up to 28 on the highway if driven moderately sanely. What will hurt you the most is getting the 5000 lbs H3 to move fast off the line- that REALLY eats up fuel.

 

I drove back and forth all weekend to my son's tournament. I got 15.8 and 15.4 averaging 70-75MPH.

I will be adding K&N this week and will give feedback in a few weeks.

 

OK i'm back from taking the kids to Disney. i drove from Northern S.C to Orlando Fla. 538 miles one way.
in the foot hills w/ five people (680lbs) plus around 350lbs of luggage. i got 13mpg+ and in the flats of Ga and Fla
i got 15mpg. i was running around 70-80. i found the h3 doesn't like hills and to save gas don't use the cruise control!
and i do have 285-18's and no mods. i have nearly 5000 miles on it now. please tell me how some of you are getting
16-18+mpg. is hummer paying you to advertise or what? i mean i know it wasn't going to get the gas mileage of
my Z but i would like to avg 16-17mpg.

 

Your speed is probably the main killer of your economy. Speeds above 60 MPH are proven to kill your economy almost exponetially as you go faster. You can do your own test on that if you want real results. I would have to disagree with the cruise control though. The computer knows what the engine needs for the current load and can regulate the fuel flow better than you can. Also, some vehicles are programmed to provide more power with the cruise then when the throttle is being manully operated. I don't know if the H3 is one of these or not.

 

Another factor with big tires is wind resistance under the truck, the higher you raise it with tires the more air going under it and trying to slow it down.

Any one know how long it takes to install the K&N 63 system?

 

I have to agree with Linus (aka Romeo)

Cruise control should improve mileage, but at anything above 55 MPH you loose.

When I drove my H3 home, the trip on a brand new engine and drivetrain, I maintained 55 MPH for nearly 400 miles and my fuel mileage was averaging 19 MPG..Never has been as good, cuz now I cruise at 75-80 on city streets and...wait a minute..I mean on the freeways and 35 to 50 on city streets and I average 15 to 16 most the times.

 

Wow! I now feel pretty good about the milage I am getting. I am averaging 18.2 I'd say 70/30 highway - city. I just cleared 9k miles, following a roadtrip Albuquerque to San Diego. (stock tires).

I have to agree with the comments about speed, I notice a significant drop (on both my motorcycle and hummer) if I am cruising above 60 - that seems to be the breakpoint.

 

I'm only getting 13.4.[:@]