Why is my fuel economy so bad?

I know that 2nd generation Tundras don’t get great fuel economy. But mine is much worse than average. I have a 2013 Toyota Tundra 5.7l v8 FFV Crewmax Limited 4x4 TRD. I run cheap Mileking tires on there (they were on the truck when I bought it). My tire size is 35x12.50R22LT E117Q. I am not a crazy driver, but I am definitely not a slow driver. On the interstate I usually hangout in the mid 70s. I do accelerate somewhat fast at red lights, but I have recently tried to tone this down. Overall I would say I drive slightly faster than average. On my odometer it says that I average 11.1 mpg. ‍♂️. I know that mud tires negatively affect fuel economy, but this seems to be too much. I think that I should be averaging at least mid 12mpg or higher. What could the problem be?

 

35's weight and size eat your fuel.

 

Reread your post and you'll have your answers.

I used to get 11.9 with 33" tires and a heavy foot.
Since I had the fuel system cleaned, I'm getting 13.4..

 

Was this a service performed or you using sea foam or the like? Around town my mileage is shit, but that's because I drive it so. On the Highway I'm getting anywhere from 14-15 when not loaded or towing my aluminum raft and trailer. With my trailer and all my gear, I'm getting 12ish. Also on 33's.

 

What exactly did you do?

 

Your answers, sir.

Mid-70s with 35s and an uncorrected speedometer is actually over 80.

Plus, add about 5% for your increased tire diameter if you didn’t do anything to fix your speedometer.

 

I took the uncorrected speedometer into account. I discovered this shortly after I bought the vehicle.

 

I assure you, nothing wrong with your truck. We are both at right about the same in everything you posted except my tires aren't cheap and my truck is quite a bit newer. Gas cost in exchange for safe, reliable, and fun transportation is wonderful! Give it the nannies off treatment and let her drink!!!

 

34’s with bumpers and I get right at 13 between 65-85mph. Both my 5.3 Chevy Silverado on 34’s and my AWD Durango with the 5.7 get 20-22 at those speeds. But hey, at least it’s a Toyota. These trucks suck with mileage but in reality it’s not that big of a difference annually. 10k miles at 13mpg is 769gal a year and at 20mpg is 500gal a year. At $3/gal that’s $2307 a year vs $1500 a year. Only $807/yr difference. Guess that is money that would maybe go to maintenance on other brands? Doubtful but whatever. Now let me go fix my hood bulge that’s cracked again and buy a $400 scanner to reset my alcohol content and go over build my rear suspension to hold up my overloaded truck.

 

As others have mentioned, 35's will suck gas. But if you just picked the truck up used, I would consider going through a checklist of maintenance items. I'd start with a differential and transfer case oil exchange; they are simple to drain and fill and often get overlooked. Choose 8 quarts of high quality synthetic 75w90 or 6 quarts of 75w85 for the differentials if you feel like paying a lot for gear oil, purchase a few "gaskets" from the dealership for the drain and fill plugs (they are copper or aluminum washers that smoosh a little when you tighten the plug down), and spend an hour or two under the truck. Just make sure to loose the fill plug BEFORE you loose the drain plug. The front diff needs a 10mm hex key socket, the rest are 24mm standard 6 point bolt IIRC.

If you are feeling a little ambitious and the differential drain and fill were easy for you, you might want to consider a transmission fluid drain and fill as well. Four quarts of Toyota WS fluid and a few more "gaskets" from the dealership, then lookup the drain and fill procedure here on the site. It's simple but you must follow it precisely to get the fluid level correctly. If you live in the rust belt, you will have to be careful about the and check plugs stripping, so be aware.

Next, look at replacing some general maintenance items: spark plugs, air filter, PCV valve, coolant, clean the MAF, etc. I recommend OE parts on pretty much all of those things. Then change the oil and use a good synthetic for good measure.

 

Similar setup to mine 10-12 mpg. Enjoy…it could always be worse!

 

I get 11.5, or so, on 33’s if it makes you feel any better.

 

Whatever it is the dealership does that I put off for 7 years.
I never thought it did anything, but they said they did a MANUAL cleaning of the throttle body.

Most said they would just pour something in the gas tank, which they probably did.
I run a couple of cans of Seafoan once a year.

I just know I got around 2.5 more MPG after it was done..
I've got better things to do than do it myself..

 

Answered above..^