How to improve MPG in '02 6.6L duramax???

[PJvH]

Thank you all for your helpful replies!

I am running full sythetics throughout, Michelin 265-75R-16 LTX/MS (recalibrated to non-stock tire size by SuperChips) w/ 55psi front and rear, just aligned, with empty bed. I start slow and look ahead to minimize using brakes by easing up on throttle when distant light is amber or red. I occassionally use Tow Haul to slow the vehicle - it increases rpm but at no cost to fuel consumption (I think) Camper shell or open bed I get the same mpg. I guess the most useful thing is to drive slower! - but in Atlanta area you get run over under 70!

Thanks again friends!

[akrockhound]

My '03 numbers are 20 hwy and 17 city, summer, #2 fuel at 65MPH hwy.

I agree that your not doing all that bad at 75mph.

[nlp]

I have the same truck (mine has 72K). I get the same mileage as you. I get 16.5-17 city/18.5-19.5 hwy depending on speed. At 75 mph, I'll get 18.5 at 65 mph it's 19.5.
I have Michelin MTX 265's and run them at 55 psi front/50 psi rear when unloaded. Other than running synthetics, there isn't anything else you can do. Mileage has everything to do with weight, coefficient of drag, but mostly speed.
Not much you can do about weight and coefficient of drag. Reducing speed helps but I'm unwilling to drive 55mph...
A bed cover helps a little with drag. Driving with your tailgate down INCREASES drag and hurts mileage, it goes against convention, but it's been proven in tests.

[More Power]

I run more air pressure in my Mich 265's, 65-70 front and 55-60 rear when unloaded. The truck handles better with a little more pressure and the tire "squat" looks correct. More pressure should decrease rolling resistance.

Jim

[kburati]

I saw a recent study that actually proved that two identical trucks tested, one with a bed cover and one without, under identical driving conditions at the same time revealed that the truck without the bed cover actually got better mpg. The bed, with tailgate up, create a circular wind pattern so the majority of air coming over the cab actually is redirected by the air circulating in the box. Conversely, the bed cover acts as a higher resistence to the air coming over the cab creating more drag. I think a cab high cap might be more fuel efficient but I no longer believe a bed cover is.

Sounds weird but I've accidently left trash bags in my bed and driving down the road they don't immediately fly out rather start going around in this circular pattern until it catches enough of the over the cab wind to pull it out of this airflow. The tailgate down causes the same effect, actually worse since you've created a longer flat level for resistance, as the bed cover.

[beeler]

My '02 makes slightly less mpg than some here (17-18.5 at 75) but maybe for reasons that have been mentioned. I live in central MT where the wind always blows. I have my tire pressure at 50 front and 45 rear. I drive alot of rough gravel roads that would shake the rig to pieces at higher psi. I tend to have a heavy foot when it comes to passing on 2 lanes. When there is a break in traffic I use all available power to make a save pass. Tonneau on or off I can't tell any difference in mpg. I also see a big difference in fuel. One station I fill at when on the road has premium fuel that adds 1 to 2 mpg most every time I fill there.

As to using the pyro as per MP's idea I have played with this for years and it doesn't always stay consistant. Imade a run to Missoula yesterday. Most of the trip at 75 mph the pyro ran at 675-700. From Great Falls to home it was raining and cooler. Pyro ran at 600-625 at same speed and similar wind. I know my mialge didn't go up when temps went down. I've checked it many times. I do believe there is a corolation but like others I can't drive 55. Heck some days keeping it under 90 is tough.