This summer I got as high as 18 mpg with my truck but averaged about 17, since August I had not bothered to check. The week of Thanksgiving I got 265/70/17 BFG all terrains put on my truck and since I have been checking the mileage. I do a lot of highway miles so I was hoping the mpg would at least stay the same because the overall ratio is now higher. Well I have been 14 mpg. There was one day I drove about 400 miles, the first 200 I got 14 and stopped for fuel and the last 200 I got 17, must have been a fluke. What is going on, a drop of 17 to 14???????

 

First, it is winter, and the fuels are formulated differently.
Second, what size tires were on there before, and did you get the computer updated for the new tire size?
Third, what load range are the new tires and what air pressure are you using in them?

 

winter gas is whats killing your mileage. they add an additive to allow vehicles to start in the colder weather. check in the spring when the gas is back to normal

 

So, you went from 255/70/17's to slightly taller 265/70/17's, right? I would attribute your perceived MPG drop for a few reasons:

1. If you didn't change your speedo calibration, you are actually travelling more miles than you are figuring, off of your odometer. You need to determine the difference in circumference, percent wise, and add that percentage in miles, to your odometer reading, before figuring MPG next time. You are actually going farther than what your odometer is saying.

2. As stated earlier, winter gas formulations yield lower MPG's, in general.

3. Colder, drier winter air, is less efficient than warm, humid air of summer, and will reflect a slight drop in MPG. Plus, some folks (like me) warm up their engines when its cold out, so of course that would hurt overall MPG.

4. Another thing to think about, is the tire pressure. If your new tires are running a lower pressure, MPG can suffer. Even a few pounds can make a difference.

A combination of some, most, or all of these things, could really add up to a significant MPG loss.

Edit: I just read the other responses...I guess kingfish made most of these points already. Oh well, I guess I should read the whole thread before typing!

 

Hey,
I put on Michelin LTS A/Ts in August and noted ~.5 mpg drop. I just did the 90k mile service with coolant, injector cleaning, tranny, etc and did the 100k mile tuneup as well (I have 91K on the truck at time of service). Since then my highway mileage has dropped to ~15-16mpg. I used to get 18 before the tires pretty easily. I supposed that it could be the gas formulations as well, but it sure seems to coincide exactly with the service. It also feels down on power a bit just cruising, but if you stand on it, it runs great. I took it to the dealer who says it's all within spec. Anyone know when the fuel formulation changes back in the spring?
Regards,
Arthur

 

Hi Everyone,
I *think* I figured out where my gas mileage went . The other night I was headed to the MIL's house and came to a stop at a stoplight where I got a big ol' wiff of hot brake pads. I said to my wife, "someone's brakes are WAY hot". Got to the next stop several turns later and got another big wiff of brake pads.... Uh-oh! Must be me!

When I got to the MILs house I touched each wheel and sure enough the right front was VERY HOT. The caliper was sticking. Curiously, it never caused a pull in the steering wheel!

So I replaced the rf caliper and the front pads and bled out all of the brake lines. The fluid didn't quite look like week old coffee yet, but it was definitely nasty. Voila! My gas mileage is back pretty much were it used to be.

Moral of the story is that if you have an unexplained drop in fuel mileage one of the first things to do is to feel for heat in the wheels to see if one of your calipers is frozen.

Also, if I'd just bled the brakes every other year I bet I never would have had the problem to begin with!