I did some testing the last few weeks and i had the following results:

I drive 55 miles to work each day and 55 home. I know its kind of
silly (my test) but when i drive 55 miles each way it take's my mind off the drive.


I started the test with the bed cover on (soft cover) gate up
filled up (18 gallons) drove 380 miles and had to fill up. 21.1 miles to the gallon.

Then drove with cover off gate up same conditions and got 310 miles before i had to fill up again (18 gallons). 17.22 miles to the gallon.

Then drove with the cover off and the tailgate down and got 385 miles before filling up. 21.38 miles to the gallon.

each time i filled up it was always around or just at 18 gallons i put in.

The weather was pretty much the same with maybe some wind when the gate was up and cover removed.

Anyway If i did this right the gas mileage is better with no cover and the gate down.

I know its not perfect science but.... let me know what you folks think

Truck is a 97 4.6 with a 5 speed and 3.08 gears flairside reg cab. 265x16's coopers.
Just an FYI if anyone is even interested.

 

Cool, you just did my work for me. Every time I fill up, I forget to calculate my mileage. (I've got a 4.6 with a soft tonneau.) The difference between the cover on and off with the gate down isn't enough to warrant taking it off (5 miles difference).
Anyway, thanks for posting.

 

The difference is with the gate up and no cover the gas mileage sucks!!!

 

Around how much would a soft cover cost?

 

How is it you only have to put in 18 gallons?

Our trucks have 25 gallon tanks...I have to put in about 23 gallons.

I only get 14.5 MPG (~330 miles to a tank).

 

I got mine for about 210 dollars. They are not very expensive. Plus you don't have to worry about your stuff getting wet.

 

Correct, but with the cover off and the gate down there isn't much of a difference. Good stuff to know

 

I never like to let it get below an 1/8-1/4 tank before filling.
Plus with the 3.08 gears and the 5 speed it gets better mileage than some.

soft cover is an extang and it was 178.50 installed, 5 years ago.
in the cold and snow its a bitch to get back on (like wet speedo's). LGJ should not have to worry about this its to warm in his area.

 

Hmm.

I usually go until my fuel light comes on.

But sometimes I have to fill up before that since I drive 20 miles one way to school (and I have to fill up at either end, use a gas card).

 

I most times fill up at a 1/4 tank which is almost always 17-18 gallons. for the test i did i just put in 18 gallons each time.

 

LOL, coolness. I think I'm going to be in the market soon for a soft cover. I would like a hard cover, but that costs way too damn much.

 

I have a 4.6 with an Extang cover. I have been keeping track of gas mileage since I got my truck, and now have 56,000 miles on it. The best mileage I have ever got was ~21 mpg. The three year overall average is 16.4 mpg. A year ago there was a short while when the max speed limit on my way to work was 55, and I enjoyed driving the limit. That caused a 1 mpg increase, which I think is pretty significant. It means I got a free gallon of gas with each fill up.

I found that with my cover off, I lost about 1/2 mpg. I never tried with or without the tailgate down.

I have found that I can really keep the city mileage up if I never accelerate in such a way as to cause my rpms to exceed 2000, and that 1750 is even better. You have to get up to about 1700 in order to get past about 43 mph. (however, crusing at 70 mph requires the motor to turn at about 1850-1900 rpm).

Anyway, I love my truck. It is strong and sure when I need it, fairly efficient when I want it to be, comfortable to drive and good looking. Best vehicle I ever owned.

 

yours seems to run lower RPMs than mine.

I get about 2000 rpms solid at 70.

 

The test was done with all highway miles and very little grade driving and city driving.

 

According to your profile, you have a '97? I have a 2000. At 70 mph, mine runs about 1900 rpm +/-. I have an auto tranny. I suspect that either you have a different rear axle ratio, or smaller tires.