Wasn't there a Mythbusters about this?

 

IIRC ( the second time they did this) it was tail gate up got the best mpg and tail gate off lost some and then tail gate down got the lowest fuel mileage. I had a 87 F150 and it got better mpg with it off then if I had it up so I say it all depends but can see with it down it can lower your mileage.

 

yes, yes there was. twice in fact.

it was a retest issue a couple years ago.

they found aminute increase with the tail gate net (not sure of exact name - has claim of better mpg on it) had an oh so slightly better result over tailgate up (1 mpg or so).

tailgate down and no tail agte had least favorable results.
this is after they installed:
- in line fuel pressure gauge
-in line fuel flow meter

then tested two exactly matching trucks from San Franciso to out towards Tracy, Ca (from the looks of the raods they showed) and ran em till they went dry.

 

yes. tailgate was was more efficient vs tailgate down or no tailgate.
there is an air net for the tail that performed a smidgen of a hair better than tailgate up.

 

one thing you have to remember about mythbusters is that they were using a different truck then the one you own the aerodynamics are different on the fords, chevys, and dodges... long beds short beds standerd cab crew cab and everything in between...... the best way is to do your own mythbusting and drive one week with it down and one week with it up then compare

 

What happens if you add a tonneau cover to the mix?
Did they test that?

 

I have a tonneau on there and I think it helps by about .5 to .75 mpg... before the washington trip a couple of months back I had the cover off and it seemed like the mileage dropped some. when we did the trip we were able to leave the cover on... on the way back got 18.2 mpg over 350 miles. mostly flat and did the speed limits 55-65.

I think though if you were to get a lighter cover than what I have, you might see even better #'s... mine must weigh 100~110 lbs (it's a brick wall)... this cover
http://www.checkerpro.com/hardcovers.html
I found after I bought mine... the pluses are that it's light and fits between the top of the bed rails and it's light, downside is you have to lock it from the inside and access is thru the tailgate.

the biggest grip I have is mine is so damn heavy, takes 2 of us to remove it. ON my 2000, it was a little lighter and if I had to I could get it off myself.

 

I've got the hard shell type, that thing weighs a TON !!

 

I got mine from XTang. It's a soft tonneau cover, but it tilts up like a fiberglass cover does. It sets in a frame,, no drilling whatsoever. Infact, I can go outside and remove the entire thing and there wont be a scratch. It cost like $350, and it looks real good. It doesn't lock, but it keeps everything dry.

 

from an old post:
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Mythbusters has had two episodes on this,
the 1st time they did a long highway test with two identical Ford F150s
running in convoy on an interstate, one with the tailgate up and one with
tailgate down, until one truck ran out of gas. The tailgate up got the better
MPG, but by less than 1.

The 2nd time they tested it was with a motor boat fuel flow gauge (Flowscan
company) retro-fitted to a Dodge Dakota regular cab. Adam claimed he had
spent considerable time 'calibrating' the Flowscan gauge.

The 2nd tests were short on a crowded California highway at 25 and 55 mph, and
they tried to read the Flowscan meter by eye to find the MPG, even though the
Flowscan will only read to a tenth so that the best they could do was notice
differences of about 2% (0.1/5.1 gallons per hour). They did travel up and
back that stretch of highway to try to cancel out head and tail winds, but
could not cancel out side wind effects. These results with the Dakota &
Flowscan meter by Mythbusters reported that tonneau cover and tailgate up were
better than either tailgate down or tailgate off. Adam's most controversial
finding with his Dakota in this 2nd set of tests was that a plastic net with
about 1 inch holes in place of the tailgate seemed to be best of all....but
only slightly.

After reporting these results, the Mythbusters said they were
'totally sick of doing MPG tests with pickups'
and did not want to get any more emails or letters on the subject.

You can watch any of the Mythbusters past episodes by downloading files at:

http://www2.digitaldistractions.org:....php?showid=mb