Gas mileage wrecked/Do not buy Falkens

I have yet to pinpoint the EXACT issue, but I had Falken H/T Wildpeaks 265/70/16s installed on my truck back in August and every gas tank I've been getting since then fluctuates extremely.

I bought my truck in 2016 and it had two A/T BFGs in the back, and two off-brand A/Ts in the front. I would get 300 miles on a tank. Google says I have an 18.5 gallon tank on my 2002 6cyl 5VZ-FE prerunner.

Fast forward to August of this year, the tread is worn down a lot and I'm due for new tires. I have Falken Wildpeak H/Ts put on with the expectation the switch from A/T to H/T will improve my gas mileage, past the current 300 mile a tank I was getting.

Fast forward to today, and I have been getting sub ~250 mile tanks since the tire change. I just got 200 miles on a tank the lowest since the tire change, and the first since my full OME suspension upgrade. What the hell is going on? I had my injectors cleaned last year by the dealer, no change. I plan on doing 33" 285/70/17 A/T tires next month, at this rate I'll be getting 8 MPG!!!!!!!!!!!!!!!!

 

Did you size up wheels/tires at all? Seems you also installed a lift? Did you install any armor or other weight?

My truck on stock suspension and 265/70/16 Hankook Dynapro AT/Ms was getting about 18.5 average mpg. After my suspension lift with a new leaf pack, and armor/sliders, and sizing up tires to E-rated mud terrain 285/75/16, I now get about 14.5-15 MPG calculated at each fillup.

If this is a gradual decline over the years in MPG, then it's probably none of the reasons I mentioned. Maybe MAF/throttle body?

 

Holy shit that's a long read.

I didn't read all of that but will immediately say; you do realize we're in the colder season right?

Winter blend fuel sucks.

 

Having added that lift though would definitely lower your MPGs a bit.

 

Try new plugs and clean the MAF, maybe

 

New plugs + wires in July

 

Well I’m in the same boat as you but I understand that I just added weight (tires and wheels) and lifted my truck and went up in tire size... I went from 17.5 plus to nothing above 14.8. I’m not mad it comes with the territory

 

Seconded on the plugs and MAF. At the very least pull and inspect them for fouling.

Also, I'll say the obvious, what's the air filter look like?

 

*omg I added a bunch of weight and turned my truck into a sail, why do my mpgs suck!*

read between the asterisks, please

 

OP To arrive at these numbers you are using a calibrated fuel cell so the quantity of fuel is a measured amount each time.

To many others factors that can`t be controlled enter into the equation to come even close to a real number

 

What were the previous tire sizes?

If a tire change were the core issue, the MPG would not 'fluctuate extremely'. Because the tires stay the same.

Calculate actual MPG. MPT doesn't exist unless you run it dry; it's just a theory. Not saying your MPG hasn't dropped, but MPT is a lousy reference point

Well, based on your cause and effect method, the suspension just cost you 50 miles per tank.

 

Are the Falkens E loaded? 10ply much heavier than a C or even P load tire? That would be the problem right there, nothing wrong with the Falkens themselves other than being heavy.

Also as other mentioned winter blend fuel ain't going to help you, and if you haven't been getting gas at the same gas station every time that could add variance.

What other mods or maintenance or weight adding to the truck have you done recently?

You're not running a K&N oiled filter are you?

Bad ju-ju junks up the MAF.

 

You have provided no useful information. Miles per tank is useless unless you drive each tank until the truck runs out of gas. What were your miles per gallon before, and what are they now? Until you know that information you're just guessing about everything. And if you never calculated miles per gallon previously you have no hard data to compare it to today. You can calculate MPG's today, but don't really have any idea how much different, if any, to the truck previously.

Your odometer simply counts wheel revolutions and does the math based on the circumference of the factory tires to calculate the distance you've driven. If you change to a larger tire the circumference changes and it takes fewer revolutions to travel the same distance. When that happens your odometer is no longer accurate. You are actually driving farther than you think. If you went to a larger diameter tire you may be driving the same miles per tank as before and just don't know it. Even if you stay with the same size tire a new one will be about 5% larger in diameter and will throw the miles off by about that much.

What size and load rating were the old tires? What PSI are you using in the new tires? What PSI in the old tires? Under inflated tires can reduce fuel mileage by 1-3 mpg

265/70/16's are an optional factory size and are the same diameter as the more common 245/75/16's that come from the factory. They are just about 3/4" wider. That should have had no real impact on fuel mileage and as you suspected your fuel mileage should be better if you replaced an aggressive AT tire.

The lift could change MPG's by 1-2 MPG.

My 2007 came with P rated 265/70/16's. Years ago I upgraded to an E rated 265/75/16. They are 15 lbs each heavier and 1" taller than stock. Same width. I did not modify my suspension. My truck still gets exactly the same fuel mileage as it did 13 years and 210,000 miles ago when it was new.

I suspect you have another issue and it just showed up at the same time as a coincidence. I also have a 2014 F150. I had new front brakes installed and new tires installed within a 2 week period just over a year ago. I upgraded to a heavier, larger, more aggressive tire on the Ford and THOUGHT for months that I'd lost 2-3 mpg due to the tires. But when my front brakes wore out after only 15,000 miles I discovered the mechanic installed them incorrectly and they had been dragging slightly on the rotors. The mechanic made it right and replaced the brakes at no charge. My fuel mileage returned to pretty close to the original mileage. I'm now about 1/2 mpg worse instead of 2-3 mpg.

 

Yeah think there is something else at play. A lot of the wisco guys I have talked to have falkens on oem wheels that are a size up and still get great fuel mileage like 20 or so. So Idk what you did but there is something wrong.

 

Put 32 in Falkens on my truck. Mpgs are still the same.

Not sure where the regear point is on a first gen , but rule of thumb with 2/3 gens is anything larger than 33in tires should be regeared.

 

8mpg is a little extreme, but tires will throw off odo and winter gas. AT tires are heavy, so eh.

 

You're in the ballpark still. It's a truck.

 

I'm lucky to get 220 miles per tank plus maybe 25 miles for tire size adjustment. So under 250 a tank city driving with ac on full time. That's driving like a bat out of hell though.

 

I remember when forums had actual information and a certain level of mechanical understanding was expected...

 

It’s possible the brakes are dragging I did new pads and rotors back in March and the rotors are already chewed through/no longer smooth