Better fuel efficiency on a pickup truck - take the cap off? or leave it on?
 

I drive a 2001 Toyota Tundra which gets about 15/18 mpg city/highway. Not the greatest at all. But, back when gas was a $1.80/gallon, it wasn't a big deal. Now that it costs about 85 bucks to fill up the tank, it matters.

Any thoughts as to whether I can get better fuel efficiency by leaving a truck cap on (where it's more aerodynamic because wind doesn't get caught on tailgate)) or if I can get better fuel efficiency with the cap off (but the liftgate up) - the cap weighs a couple of hundred pounds I think.

Mythbusters did it. If I recall correctly the best mileage they got was cap-on-flap-closed.

I think Mythbusters just did the "tailgate up/tailgate down" thing. You get better gas mileage tailgate up, because you create a "bubble" of air in the bed/behind the cab that almost acts like a cap. I don't remember them doing the same thing with/without a cap, but they did do windows down vs. AC.

the difference will be negligible. unless you want to do some serious streamlining, in which case you might as well look at another car like a sports coupe, you can´t expect to make any decent improvements.

I think it was in a "viewer-requested follow-up" episode...

If you can find a camper top that tapers toward the back, you'd get better mileage than anything else. A teardrop with the back end cut off is most efficient because it eliminates much of the vortex-induced drag that other shapes have.

I don't recall the Mythbusters doing covered or uncovered, but they certainly showed that gate closed is most efficient because you don't get vortices so badly.

Seeing as the "dead zone" inside the truck came in part from the gate creating a baffle that locked in a mass of still air behind the cab, then capping the bed would just kill that dead area and add a lot of weight, so it could be a lose/lose.

I'd want to see results of 3 things - gate up, no cap; gate up plus cap; gate up plus tarp.

If you regularly do the same drive every day, fill the tank to the top, run the vehicle for a week, re-fill the tank to the top and run for a week with the cap on, and re-fill the tank and run for a week with a tarp on.

After three weeks, look at how much fuel you used each week, and you'll have your answer.

not sure about the Toyota ECU, but my wife left her gas cap too loose on her Acura TSX and it set off a CEL ...check engine light. When I tightened it, it went away after a few minutes. The fuel pump suction would be effected not sure what else pro or con it could do since the amount of fuel used is determined by engine load/conditions not tank pressure.

Dude, wrong kind of cap.

That's what's called an evap code. They're bad.

The mythbusters also did it on a short bed pickup. Effects would/could be different with a standard cab and full size bed, as well as with older trucks vs newer ones which have much better drag coefficients. Just experiment with it.

ooopps :eek:

Don't bother with what you "remember", here's the official results from Mythbusters:

Episode 43:
Myth: It is more fuel efficient to drive your pick-up truck with its tailgate down, rather than up.
Status: busted

Driving with the tailgate down actually increased drag on the pick-up and caused it to consume fuel faster than the identical truck driven with the tailgate up. It was later revealed that the closed tailgate creates a locked vortex flow that created a smoother flow of air over the truck. With the tailgate down the trapped vortex was dissipated and the drag increased.

Episode 64:
Myth: REVISITED: It is more fuel efficient to drive your pick-up truck with its tailgate down, rather than up.
Status: re-busted

Using a calibrated fuel flow gauge, Adam and Jamie first re-busted the tailgate up vs. down myth, then went on to test various other truck configurations (hard top, mesh tailgate, no tailgate).

Episode 64:
Myth: SPINOFF: A plastic mesh tailgate provides superior fuel efficiency compared to the standard metal tailgate.
Status: confirmed

Again using a calibrated fuel flow gauge, Adam and Jamie proved that the mesh was the most efficient way to configure a pickup truck.