Gas Mileage Much Worse With Age?

Within a year, with the same load, the same maintenance, the same trailer, the same cargo, my 2015 Tundra SR5 4x4 double cab, bought new, went from using 17.9L/100 to 19.9L/100. That translates to about 1 gallon more per mile in fuel consumption. That is the change from one year. Can I expect worse as this truck ages. Dealership service manager just shrugged his shoulders.

 

With my 2021, I am experiencing something like that currently and I only have 3000 miles on it. 3000 miles since December when I bought her.
I can tell you to the day when I noticed it. There's no reason for except this.
Fuel depots who do the mixing of the gas before it goes into the big rigs for distribution at times do things for reasons of financial business performance.
I'm old enough to remember the "gas shortage" from way back and my dad complaining that "the gas is like piss water" when he noticed his mileage going down somewhat.
If you feel strongly about it, take a small sample from your car if possible and have it measured for specific gravity / energy output.
Just a reduction of .1 in octane can have an effect in mileage.
Could be that and hidden behind the "we add in alcohol at various times of the year" thing some fuel truck guy told me.
I was getting gas for my WS6 one day and I told the truck driver at times the gas is better than other times.
He said it could be the blending plants at times or the age of the tanks in the ground that could be accumulating some moisture.
Change gas stations for a while and see if that helps. I've seen more than a few stations here in CA. dig up tanks and get them replaced.
A quick way to see if they have been fooling with the blend to "make more with less" is to buy a bottle of octane booster.
Add it at fill-up and measure your normal running around. If mileage goes up, it's a "gas quality issue".

 

IMO part of it could be you. When a vehicle is new, you might tend to drive a little easier, a little more careful, and since MPG is an emotional issue for most, with an eye on maximizing MPG. You might have even been careful about where you buy your gas. But over time, you become a bit more casual about it all, maybe stick your foot into it a bit more entering onto the highway, or you race to get around the car in front of you that when new you would have been happy to just stay behind. And maybe you are carrying more stuff all the time..adding under seat storage, etc. All those little things can certainly add up.

I keep a spreadsheet of every gallon of gas and the mileage for our vehicles. I have never notice any real decline in MPG over the year. My wife's 4 year old CRV is still getting the same MPG as year 1.

 

I would agree with @LuvTundras. My 2nd gen with 235k on long road trips just fam and some stuff gets about 18mpg on cruise control @ 72mph. Pulling a trailer, about 6000lbs I get about 13.5 mpg @ 65mph on CC. I also keep a log using trip A and odometer, cross reference and do the math from there..

 

My '13 Crewmax gets the same mileage at 165K miles now as it did when I bought it used just under 6 years ago with 30K miles.

 

Is that a long-term average or a single tank? Unless you drove through haboobs with a cotton air filter and scored your cylinder walls it shouldn't lose mileage. If anything it should improve slightly as the bearings wear in and lose drag.

If you got new tires, that often reduces fuel mileage. New tires have more tread and are more supple rubber which is great for traction but absorbs more energy as they deflect under the weight of the vehicle. As the rubber hardens it rolls better.

Ever drain and refill the rear differential? The factory fluid can get nasty, gooey, and thick if conditions are right. It was the first thing I did on my used Tacoma when I bought it, and I'm glad I did. It was only 5 years old but so thick it took over a half hour to drain out when HOT... then again it was a testament to Toyota's gearsets I suppose because they didn't fail, at least in the 50k miles I put on it. It would have a slight whine on the freeway when cold for the first couple minutes then ran good as new.

 

I’ve been playing around with the mileage game since I bought my new 2020 tundra back in June of 2020, when I first got it I noticed I was passing a lot of other tundras so I thought to myself, hmm…upon reading many replies and views on this website I decided to keep my RPMs below 2000 and drive at 72 to 73 with cruise control on, then I saw other tundras passing me, ha ha, this gave me 18+ miles per gallon which I thought was worth the extra time it took to get from point A to point B

 

Have you cleaned mass air flow sensor?

 

This is clearly a "quality" engine oil issue.

 

there are a lot of factors, maintenances, tire pressure, traffics, weather condition...

 

Summer gas blend

 

How many miles on your truck? Kept up with maintenance- spark plugs, filters, etc?

 

147,318% ^^^^.

 

This and throttle body, fuel injectors, air filter, oil, gas grade, tire pressure etc. there are several components to look for that could help