Actually, that tailgate tip is not true, according to some engineers. It goes against intuition, but leaving the tailgate on and up on a pickup is better. See here for an explanation on the Car Talk site. According to Ray, aerodynamics is a very complicated science, and air doesn't always move in predictable ways.
All the wind tunnel tests and expert analysis apparently doesn't refer at all to my 52 Chevy going down the freeway....
Here are my actual real-world daily driver gas mileage experiences, which can easily be repeated to proof they are 100% correct.
Putting the tailgate down, hanging on the chains,
will give a clear measurable
improvement in gas mileage, the longer the distance driven at high rpm/mph and high wind drag.
In fact, the faster you go and the longer the distance, the better the gas mileage.
Here are the numbers:
Once a month I do a business trip of about 200 miles of pure freeway driving at 2500-3000 rpm and 65-75 mph. I am using 91 octane gas (highest you can get in CA). See engine specs below...
With closed tailgate I get about 17 miles/gallon, but with open tailgate on the chains, I get a little over 20 miles/gallon.
That's a measurable
increase of 20 % in gas mileage for prolonged freeway driving.
These numbers are with an unloaded bed.
But check this out - when I hauled a fully loaded bed up to the rear window with a two inch drop on the rear tires going the same route and distance, I also got 17 mpg just like driving unloaded with closed tailgate !!
So the engine works just as hard with a fully loaded truck as unloaded with tailgate up.
Unbelievable how huge the wind drag works against the engine on the freeway and high speed.
City driving has considerable less wind drag and the tailgate makes little to no difference if up or down.
Driving, maintaining and understanding old trucks is not rocket science, after all.
Wind tunnels are not the same as actually freeway driving with an engine creating the wind drag, rather than a giant wind machine...
I don't know how other trucks behave in this simple freeway test, but it doesn't cost anything or take any effort to let the tailgate down, next time you drive down the freeways at high speed.
One more note: I don't do this to my engine, but I imagine gas mileage goes down again, if you go past 3500 rpm for prolonged periods.
The cool thing about old trucks is you don't have to be an engineer or expert - these trucks and engines actually talk to us ... all you got to do is listen and have fun with them.
