RES4CUE

You're talking 72 miles lost per tank (assuming 36 gallon tank) which equates to roughly 4.5 gallons at 16mpgs.

That's roughly $14 lost by having the tool box which I would take the convenience of the tool box all day long!

soar07

[QUOTE=Guntherman;3163656]I recently noticed a dive in fuel economy. Some theories:

• Winter gas
• Tires wearing down so now they're smaller diameter, screwing with shift points, programming etc.
• Increased headwinds because of changing seasons
• Aging vehicle

Then I remembered my mpg dropped right around when I installed my toolbox. It's a Delta single lid crossover, high profile, nothing fancy. I watched the 2009 F-150 aerodynamics video where the engineer talks about how the truck is supposed to direct airflow toward the tailgate which is designed to efficiently transition the airstream to turbulent flow, minimizing the coefficient of drag. I noticed immediately after installing the toolbox that morning dew and rain accumulated and moved around on my back window, when it had not previously. My prevailing hypothesis became that the inefficient aerodynamics of the toolbox interfered with the efficient aerodynamic design of the truck.


As an engineer, I immediately set about testing my hypothesis by trying to find a 3D model of an F-150 that I could import into Autodesk's Project Falcon aerodynamic modeling software. I became frustrated at the absence of free 3D F-150 models on the internet and also became irritated at not understanding the nuances of the software.


That's when my wife, the psychologist and voice of reason, said, "why don't you just take the box off the truck and see if your mpg improves."


Long story short: I was getting 16.7 before. Now I'm back up to 18.6. I tried to keep all conditions the same to not skew the results of this experiment. I'm fairly confident in the results after 800 miles or so.


Hopefully this helps someone trying to solve their mysterious decline in fuel economy.[/QUOT
I put in a composite toolbox myself and saw MPG on my 2018 Drop at least 1 mpg or more. After reading this I am going to put it in the bed also.

mccljp

Wonder how a bed cover affects the MPG

marshallr

A 9 year old thread.

But let's just say you'll have to go several places to the right of the decimal point when doing the math to see any difference and it could be + or - what you're getting now. I don't believe for a second that the OP actually lost 2 mpg 9 years ago by adding a toolbox. I've owned trucks for over 40 years and have never able to see any difference at all regardless of what I had on, or in my truck. And I've had toolboxes, caps and nothing. Of course, I only go 1 place to the right of the decimal point when figuring fuel mileage.

There have been dozens of tests by every major truck, off road,and car magazine, Outdoor Life, Popular Mechaincs, Myth Busters etc. going back to the 1970's. They looked at trucks with nothing in or on them, caps, bed covers, toolboxes, tailgate up, down and removed. The results have all been pretty much the same. In some cases they noted a fraction of 1 mpg better, others a fraction of 1 mpg worse.

If that were true, we'd be talking about how many gallons per mile instead of miles per gallon.

How much time you spend standing on the skinny pedal is the biggest factor in determining fuel mileage. Keeping enough air in the tires can make 1mpg difference and towing will make a huge difference.

Siber Express

Just to go one further in this 9 Y/O thread, if you leave a 6in gap between the tool box and the front of the bed or close the underside of the toolbox in so the air stays out the pillow of air remains.
I loose 1-1.5 MPG between the Tonneau Cover and the Shell and my tailgate gets more dirt on it with the shell. I have not had either off to tell you the mileage with out either.