I have put a commercial circular bar rack on top of my truck and the MPGs have gone down from roughly 18 mpg to a spiratic 15, 13, or even 11MPGs. Is it because of the rack or what? I wouldn't think it would hurt the MPGs like that because the truck obviously has more power than most gasoline engine cars and that kind of drop in MPGs usually will show in gas cars like that. I would like everone elses opinion because that rack isn't exactly just an on/off in two seconds kinda deal. I have thought about air deflectors for roof racks, but two problems: A) Very expensive B) Will it or will it not do any significant changes? Well I thankyou in advance for any suggestions and opinions.

 

I have a buddy that has that problem when He puts a roof rak on his Jeep but I wouldnt think it would matter a whole lot on our trucks. do you do mostly highway driving and are you now hualing a lot more weight becuase of the rack? Those are th only two things I could see make the MPGs go down like that.

 

No I don't haul much on it. Most of my driving is highway, but its to and fro work or just out and about, nothing is ever hardley on it. I bought it for the kayak, even though 8ft bed, and 8 or 10ft kayak (short kayak) the toolbox takes 2ft away from bed space (sometimes annoying), so I got the rack to put it somewhere without damaging the kayak. Like i said though its hardly ever up there. During cold starts, which have been going on for a while now, it burns oil for about 1 or 2 minutes then it stops. I've been trying to remedy that, but that wouldn't be causing that big of a problem as far as that goes would it? This is strange, I'm guessing take it off and see if it improves gas mileage? I really don't want to do that though considering how it clamps on to the raingutters using plates and bolts which have to be perfectly coordinated with each other.

 

anything up top disrupts the natural airflow over the truck, you eliminate the "swirl" effect that develops right behind the cab. this circular air motion is critical to aerodynamics on our trucks which results in the loss of mpg.

 

i get that kind of millage towing i cant see a roof rack having that kind of effect 1-2 mpg maybe but not 6 mpg

 

Yah I guess taking the rack off and see what happens. That just means when i want to use it I will/would have to put it back on which takes like a half hour.

 

How long since last oil change? Haqve you checked the FPR screen? Fuel filter?
Contrary to popular belief, you WILL get more mpg with tailgate up opposes to anything else, as mentioned above.

 

I'm getting close to my next oil change. My fuel filter does not look that dirty. I don't know what an FPR sreen is, that maybe the contributing factor considering I've never checked it since i bought the truck (this spring). My tires are 5 psi low due to weather changes lately, but they wouldn't have that big of effect would it? I'm airing them back up regardless.

 

Yes, incorrect air pressure (high or low) will have an effect on MPG and tire wear.

Your FPR (Fuel Pressure Regulator) screen (and fuel pressure) should be checked. If the screen is clogged, it needs cleaning.

Do a search on "FPR Shim" and that should get you info on both checking your fuel pressure and how to find and clean the FPR screen.

You didn't mention how much frontal area your rack has. Increasing the frontal area of the truck (whether in front or on top) can also have a dramatic effect on MPG.

Think of it this way...your truck is as aerodynamic as it can be straight from the factory. Anything you add to your truck (including bug deflectors) increases drag, causing your truck to work harder maintain the speed you normally drive. The items added to your truck increase weight and, if the item (rack in this case) has solid vertical front, sides and back, you've added another "truck bed" that air flow must go over or around when you're moving. Once the air flow passes over the rack, it encounters the truck bed in a different aspect than originally designed. Now the air flow must go over this area. It's like you've added a wall to the top of your truck and a parachute to the back of your truck because the air bubble doesn't form as it should.

Personally...I'd remove the rack and spend the half-hour to install it when needed. You may not the hassle of the extra time, but your wallet will appreciate it when you're ready for fuel.

By the way...Welcome to

 

i would say remove the rack and run one tank of fuel through the truck, then see if the mileage goes back up before you do any other changes to the truck.

 

X2 on Joe's idea, might as well isolate the problem.
As for other ideas, i have a hard time believing that a rack would make 6-7 mpg difference...
maybe 1/2-1... two if you drive 85... lol
There are alot of things you can do to improve your mileage...