Actually they did on the revisit they did, 2nd gen Dakota.

MythBusters - Tailgate Up or Down 2

 

Good video. I would have thought the tonneau cover would have been the best. Interesting...

I wonder about if you have a full camper shell on there?

 

if the tonneau cover was lighter it would my campershell is really bad on my gas

 

the only thing that they didn't do is fill the tank before each test...because you'll get better gas mileage running less than half tank of gas

 

What's the logic in getting better mpg on half a tank as opposed to full?

 

the truck runs lighter. your not hauling around all the weight of the fuel then. the only down fall is it can ruin your fuel pump

 

they made each run 5 miles they used 3 gallons max in this whole test but my fuel mileage is about 10-12 max the way i punch it everywhere because i dont mind paying

 

Don't mean to argue, but gas weighs about 6 lbs. per gallon...so half a tank is only about 66 lbs. Probably not enough to affect mpg. My tailgate, bumpers, beer coolers weigh more than that and they don't affect my mileage.

 

intresting but then a full tank would be around 132lbs it would probably be around .4m/g change per gallon,hmm. your beer coolers might be compensating the weight if there full.
now you got me confused on this because i always run light, if i put 10g(and thats coming close to running out) in twice that gets me about 460miles and thats driving 26miles a day, if i fill the tank then it gets me about 350miles driving the same distance doing the only 5-6miles over the speed limit( I can't afford anymore tickets,lol). now i'm confused...

 

Hmmm...your figures add up to 23 mpg...460 divided by 20. That's excellent mpg bro...what kind of truck is yours? I know its a 93 LE like mine...but is it 4WD or 2WD? four, six or eight banger? Mines got the V-8 and is 4WD, auto tranny and I'm lucky if I can get 13 mpg in town...no hills, straightline flat terrain out here on the Plains.