Mythbusters just did a test on this. Matter of fact, i watched it about 3 hrs ago. They used identical new Ford trucks, drove on full tanks, one with the tailgate up, the other down. The truck with the tailgate down ran out of fuel 30 miles before the one with it up. They found using scale models that with the gate up, it recirculates the air and causes air to flow directly up and over the truck. With the gate down, the wind blows down off the cab and causes drag right on the back few feet of the bed/ tail gate area.

 

how much drage does a camper shell adds?

 

what about gooseneck/5th wheel slotted tailgates....do they help or make your mpg worse?

as far as a camper shell....by the link at the beginning of this thread, it causes better mpg than with tailgate up or down by decreasing engine load.

 

muser... or anyone else if your still around I have a question for you. What year or type and from what vehicle would I look for to get a MAP unit as i'm not into newer vehicles?
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Not sure why one would want to buy a pickup and then put a camper shell on it, but I would think the mpg would not be much different than an Excursion since I thought the same frame and pretty much the same HW was used...

 

I have a 2000 Ranger XLT 4x4 auto with OD and a 3.0 litre V6. I have tried highway driving both with the tailgate up and OFF (I hever tried it with the tailgate down because I think that is dangerous in case one gets rear-ended). I have been driving with the tailgate off for about 6 months now and I have not seen a change in my gas milage. The very best I can get is 24 mpg doing 55 mph on the interstate, but I usually get 18 mpg in the warmer months, 15 mpg in the colder ones (or less). Today I saw a program from Mythbusters about this but they never demonstrated it with having the tailgate off. They showed there is more drag with the tailgate down. I know that on windy days when I am driving into the wind while on the interstate, my truck feels like it is not working as hard when the tailgate is off but I have not seen any change in mileage, though. My last trip useing the interstate was interesting, though. My first route was into the wind. It was so windy that for my truck to run at its lowest rpm at 55mph, I had to have the OD turned off. On that trip my truck got 14 mpg. On the return trip, since I had a tail wind, I turned the OD back on but I still got just 14 mpg, uff da.

Orki1960

 

I saw the same program Torque1st. Interesting! Several years ago the Archer brothers used to race pickups and tested this exhaustivly on the race track. Both brothers used identicle trucks, one with the tailgate up and the other down. Running at the same time the gate up truck gave measurably quicker lap times. All things were equal

 

I don't know exactly, but I would think any mid-90's GM car or truck would have the MAP sensor you're looking for.

 

Thanks EPN, at least i'll have a model year zone to look for, thanks again as i'm stuck in the 60's with carbs.
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Rather than mess with a map sensor and trying to measure voltage, the correspond it to a vacuum number to determine efficiency, why not just get a vacuum gauge permanantly mounted in your truck? I have. It's cheap and easy and tremendously influential in my driving habits.

 

A vacuum gauge is the very best thing you can do for mileage!

 

I'm running a vacuum gauge for the last 33 years in the F250, it's hard to split 1/10 inch on a vacuum gauge with any repeatable accuracy hence MAP reading to a DVM.
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A vacuum gage helps correct bad driving habits that can boost mileage. You don't need to read it close for that. It is just a reminder that you have your foot too far thru the floor...

 

If all you want is a vacuum gauge to watch go up and down while driving then that may be ok for you, not me as mechanical will stick and isn't as sensitive to small changes. I have many different styles of baffles that I run in the exhaust tips (4 1/2" x 19") on a custom X dual exhaust system, with each different design that makes the motor respond differently at low 800 rpm's as well high 5,500 rpm's. With the different pressure readings at the O2 sensor location and manifold pressure with a MAP gauge I can tune "nats a$$" vs ballpark as ballpark isn't close enough for me. With a 68 CS, 3 tanks (56 gallons), C-6, 410 and 14.2 mpg on a carb I will tune with a MAP gauge.
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For all of you that missed Mythbusters a few weeks ago, they proved that driving with your tailgate down results in worse gas milage. When two identical brand new F-150's were driven exactly the same speed, the one with the tailgate down went 30 less miles than the one with the tailgate up.

They showed how this works in a water tank. With the tailgate up the air formed a bubble in the bed of the truck that the fast air just went over the top of. With the tailgate down the fast air went over the truck and hit the inside of the bed creating more drag.

Everyone on the show was as suprised as I was by the results, but you can't argue with Mythbusters. Well you can, but I'm going to trust them.

Happy riding with your tailgate up.