mmm these are all different readings in mpg, I am a conservative driver and i get about 18mpg, maybe it's the area where we all live in

 

I as well am a conservative driver. Literally, I run even with tractor trailers when I get up to speed. Often times them passing me. I'm a granny until I hit the trails.

 

I was getting around 15-17 when I first got the truck. The single best thing that has made a dfference in improving my mileage is switching to full synthetic oil. I use amsoil 5w-30 in the crank, the low-viscosity fuel efficient ATF in the tranny which is a direct sub for GM's DEXRON VI and just drained/refilled the differentials with the syn. Of course the intake is no longer stock and the tranny coller has been rerouted to it's own radiator which saves the motor from having to let out the fan clutch as much as it used to. My ScanGuage tells me I'm getting 22mpg on the highway. Usually goes down a bit in the colder weather/with extra weight/towing. She's still a pig when doing local though but then again, any car is not going to be efficient local unless its a hybrid in which case there is a $3k-4k premium on those so you're really not saving money anyways.
My cousins 07 Jeep Grand Cherokee with the V6 was doing about 16hwy on a good day and that truck weiged about 1200#'s less than the H3. My dad's 2010 M Class has a 6cyl. with a 7-speed auto trans and that is only getting 18hwy. So all in all the H3 isn't that bad for it's power-weight ratio and also taking into consideration it only has 4 speeds to work with.

 

I'm pretty sure when our low fuel light comes on we have 1.5 gallons left


I have an all base 3.7 with a 5speed:

Few hundred pounds packed up and going between 75 and 80, I averaged 17.4 mpg

Emptied out and sticking to a strict cruise at 65, I averaged 23.0 mpg

pretty good I thought

 

that describes me exactly as well

I used to be the guy flying by everyone doing 85 or 90, now I enjoy the drive, listen to something enjoyable on the radio, and make my fuel last longer

funny thing is is I'm probably getting better gas mileage now in my H3 on the highway than I was in a 2.8 v6 Fiero GT flying down the interstate

 

Wow so you got all that mileage by simply upgrading to synthetic fluids and an intake? Airdoc intake I'm assuming? Thats pretty awesome. I've been planning on making the move to synthetics as well I'm just waiting for the right time to do it.

More than that.. when my low gas light comes on, I can usually get a good additional 40miles before I fill up. Which is at LEAST 2 gallons.. probably closer to 3 gallons.

Hell ya. My wife and buddies always yell at how slow I go, so I speed up and go 80-90 with the flow of traffic. But then I also slam on my brakes and go 50mph when they all hit the brakes. So I had to prove to them that grannying it and setting cruise control for 6-7mph over the limit will get you there just as fast as hauling *** and then slamming on your brakes every 2 minutes.

 

It wouldn't say it was all b/c of just the syn. oil, but switching over made the biggest difference out of the other mods I've done to the drivetrain/chassis... at least from what I've noticed. All the stuff I've done to my truck has been in dribs and drabs, not all at once. Also forgot to mention I don't have the stock exhaust. Put a Magnaflow on so I'm sure that helps a wee bit as well.
If you are thinking of switching oils, I would def. suggest doing it. Not only does it provide less friction/resistance on the drivetrain than dino oil, but you also have the piece of mind knowing it won't breakdown nearly as fast as dino oil. So if you go over mileage on a scheduled oil change, you needn't worry too much. Amsoil claims its service interval can be 12,000-15,000 miles depending upon what grade you buy. If memory serves me correctly they have one coming out that may have a 25,000 mile service interval but don't quote me on that. I change mine every 6k anyways. The only dowside to syn: Once you switch over to syn, you should never switch back. With dino oil, the gaskets and seals expand within the engine. This does not happen with syn. The gaskets and seals contract to their original dimensions so if you were to switch back from syn. to dino oil, you risk cracking some seals/gaskets. This could cause seeping or even leaking of oil in spots. Some of the newer materials used in gaskets/seals/flanges/etc. in new vehicles are immune to this. This mostly effects older vehicles. But b/c we can't catagorize and know all the compunds in each little seal, flange, or gasket in the drivetrain, I would still never switch back once syn. is put in. Better safe than sorry. I learned this the hard way a cpl. of years ago when I used to be a motorcycle mechanic and was working on a BMW R90 flat twin. One of those things they never taught you in school back in the day when syn. wasn't anywhere near mainstream.
You're right too about the reserve. When the low fuel light goes on it has to be at least 2 gallons. I've been in situations where I had to drive it until it was on fumes and put around 21 gallons and change in. She can only take about 18-19 gal. when filling up right after the low fuel goes on. I think the total tank size is 23 or 23.5 gal. if memory serves me correctly?

 

Well just as a warning, f5stop (the HUMMER engineer from the forums) has said GM has found that using synthetics in the HUMMER transmissions will deteriorate them over time. The immediate results are good, but over time they fail prematurely. Just as an fyi.

But I had some free oil changes to put thru the HUMMER and they didn't cover synthetic. But next time it gets an oil change, I'm def. going synthetic. I'm def doing synthetics in the diffs/tc as well. I've used them in other cars to great results.

I'm pretty sure our tanks are 23gal tanks. I've def. taken my truck down to needing 22.5 gallons lol. THAT was a close one. In the middle of friggen nowhere VA or WV and no gas stations for milessss.

 

well i drove to springdale, ar today in the H3 and slowed it down to 71-72 and averaged about 18mpg. so the ticket is slowing down.

 

Where in AR are you from. I'm in the SW corner in Magnolia.