H3 3.7 07 adventure So my wife is going to be driving my h3 to bring the kids to school until we get a new lease. I honestly am getting 10 city and 13 hwy with a 3.7. I honestly don’t know why I am getting this bad of mpg search tons of forums looking for a answer. Got all my fluids changed. Tb cleaned MAF cleaned. Air doc added, pcm tune, changed o2 sensors. I didn’t buy the hummer for great mpg but I am not driving a alpha either. Any serious ideas that I can try.

 

Tire size, tire PSI, fuel being used (cheapest available vs top tier), have you inspected the brakes for caliper piston corrosion causing brake drag?

 

285/75r16, 38 psi, speedway 87 octane, No I haven’t inspected for caliper piston corrosion. I guess I can start there. I thought brake drag would be a issue if the vehicle didnt roll on a flat plain the h3 does.

 

@Doc Olds i went and checked just the rotors at lunch. The front has grooves like they are going bad the back is smooth. So looks like I will be replacing the front & back. Throw the money at it. Hopefully that is the issue that would be great.

 

May I suggest doing the fronts first, then see if there is any improvement. You may need to do the backs too, but maybe later? These trucks are getting older, age itself can deteriorate systems.

 

I got all the parts for front and back for about 174 from Detroit axle. So I am going to just do them both and knock it out of the park with a complete flush also. Then let’s say that isn’t my mpg issue any other suggestions? I mean I would be happy getting 14 around town

This is my mpg currently. The last was a highway trip about 150 miles.

 

Keep in mind H3s are heavy, and the I5s can move them pretty well, but your biggest fuel use is like 0-30 MPH. Start out slow and easy. Mashing the pedal to stay out front of traffic will kill the MPG in these things.

What speed do you drive in your highway trips? Once you break 70MPH, fuel efficiency plummets.

Back to your answer to my fuel question.... Speedway is cheap crap and is not helping anything in both the mpg or fuel injector cleanliness departments.

 

I been taking it easy. I try to stay below 2k rpms. This highway trip I was 70-75 mph. What gas company do you recommend? Also another interesting pic

07 hummer mpg avg on Fuelly

 

I use Marathon almost exclusively. USA brand and the largest refiner in SE MI.

All depends on what part of the country you are in. Look up Top Tier Gasoline and look at what brands are near you. "Top Tier" is a regional term, not really used in the upper Midwest, but it gives you the brands that use detergent additives recommended by vehicle manufacturers. Keeps things clean and first step in avoiding rough idle etc..... If you stick with good fuel, you never need BS magic gas tank additives to resolve poor fuel use problems over time.

 

i am in Michigan. I will start using marathon. Doing the brakes tomorrow and will give a update