Hi all, I'm new to the site, thinking of moving to a V-8 H3 from my 02 2500HD 6.0 Chevy. My 02 6.0 gets 11/14.5 MPG weighs 6200 LBS. My concern is why do the V-8's only get 13/16 MPG, when the chevy 4WD silverado with the 5.3 is rated at 15/20 MPG? Is it because of the AWD?Does the H3 have theDOD engine and usethe same trans as the 1500 pickup the 4L60E I believe?Why wouldn't GM use the same powertrain package with the 5.3 as the trucks for a little better mileage? Seems likethe H3 hassome steep gearing in them. Does anyone know how many revs at 70 MPH they turn? Sorry for all questions. Great site. Thanks Dave

 

Box vs somewhatof astreamlined truck

The square box shape does nothing to enhance your mileage. Also, AWD will play some MPG tax too... so will larger wheels, etc.

 

My first tank of fuel put my mileage at 15.8mpg's in the Alpha.

 

Wow... I'd love to be able to track MPG more accurately in the truck. 15.8 average actually sounds great. I monitor my fuel economy on a spreadsheet and my average over 24000 miles is right at 16 mpg with the 5 cylinder.

As for what affects fuel economy, I read somewhere that the LED tailights in Toyota hybrids are projected to save 0.1 to 0.2 mpg alone over conventional bulbs. So, basically, every little thing impacts fuel economy - obviously, though, the bigs ones are still gearing, aerodynamics, tires, AWD.

 

You have to look at more than engine size for MPG. The final gear in the H3 Alpha is somewhere around 4:1, I would imagine most pickup trucks have between 3.50:1 to 3.75:1 ratios depending what options come with the truck such as trailer packages. When your rear gear is that low you have plenty of grunt but you pay for it at the pump.

 

Notice that the Silverado's HP and torque are higher than the H3's too. I'm guessing here but they probably had a harder time fitting the 5.3L V8 into the H3 engine compartment and there could be compromises on the intake and exhaust that don't allow the engine to breathe as freely or operate as efficiently. They also may have changed over to some less expensive internal components that yield less power/mpg vs. the Silverado. As was said earlier, the 4WD operates in 2WD most of the time, especially during MPG tests and the H3 is full time AWD/4WD.

From Carlist.com http://www.carlist.com/autoglossary/...ossary_41.html
This is the ratio of the gearset (usually the differential) that is farthest from the engine. A ratio of 3-54:1 means the driveshaft turns 3.54 times for every one turn of the wheels. Generally speaking, the higher the number, the better the vehicle's initial acceleration and pulling power. The lower the number, the better the vehicle's fuel economy.
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http://www.scangauge.com/
The best purchase I ever made because it tells you how to manage your gas mileage

 

One more thing is that the 2008 EPA MPG estimates are lower than the previous ratings, so be sure you are comparing the 2008 H3 Alpha figures to the 2008 Silverado figures. They changed the testing procedures to more accurately reflect modern driving since the previous standards came from the 50's.

My 2007 manual H3 initially was getting 15 mpg but now after 7300 miles its hovering around 17 mpg. I drive like a grandma when accelerting from a stop (shifting at 2K-2.5K rpm) and try to keep it under 75 on the highway in flat Florida and the best I've gotten so far was 17.6 mpg. BTW - I just changed the oil to Mobil 1 5-30W and there was no difference in gas mileage over the same routes with non-synthetic oil.

Jeff

 

Wow Hummer Mike, my first tank was 10.2 mpg. Getting better up to 12.2 mpg today. Slowly breaking it in.

 

That's so strange, I can get around 20mpg on the freeways provided I stay at or below 70. I've had arond 400 miles on a tank and just be a tad under a 1/4 tank with all highway miles.

I haven't really looked at my city driving carefully, I don't do a lot of that as I'm usually driving my company ride. I know it's better than 15mpg avg. though.