Diminishing MPG.... why is this happening!?

Yes, California gets winter gas too. Everyone in the US gets it at around the same time.

Tires, especially if you do in town driving (accelerating more rotational mass) and winter gas together is worth about 3 mpg.
One thing nobody mentioned is you "opening" up the intake and exhaust. You realize that even with no air filter the engine gets no additional air correct? Your ECU will adjust the air/fuel mix accordingly, regardless. As a matter of fact, there have been dyno tests on this truck that shows NO air filter installed actually made less HP and torque than aftermarket or OEM.

If I were you,
I would throw the K&N in the corner and install the stock filter. Check results.
Make sure your tires are properly inflated.
Wait until end of this month when winter gas is phased out and summer blend is put back in the system.

 

Exactly, the intake adjusts to air flow.

That’s why the stock air filter really never gets dirty, it just lets in less air.

It’s a “dirty” little secret that nobody admits.

 

If I had to guess, I'd say it was likely just witches putting a curse on you. Happens all the time.

Burn them and you'll be fine.

 

I just noticed a 2-3 mpg hit also. I also just replaced the stock 265/70/16 Goodyear Adventure terrains with 265/75/16 Goodyear Ultraterrains in SL...(40#)
I thought I was being pretty conservative with these Ultra terrains as I really wanted to go 285's in a Nitto Ridge Grappler! I also sat in the truck while it was running for a good 20mins after work the other day, which should have only affected that days mpg total...?

 

It's a little bit of everything. But mostly the tires. I just put 265 75 16 wildpeaks on mine. One month. Same gas. All winter blend. Same driving. 1.5 mpg less. You have to pay for the increase in rotational mass, tread pattern and depth. The air intake and exhaust cost a little. More air equals more fuel. Weight in the bed doesn't add as much a you think. Do you get less mpg having four grown men in the truck? Sorry ass motor if you do. A couple hundred on rolling weight won't matter.

 

If ya want to stay closer to stock mpg with a larger dia. tire, go with a 255 series, pizza cutter. That’s my plan.

 

Do you go with e rated, c rated or an SL rated tire? I'm willing to bet you got an email rated 10 play heavy ass tire killing your mileage.

 

Every state is required to after September 15.

 

Might want to try more pressure in the tires. I run 38 cold in mine.

 

I think this thread and a few others just shows us how difficult it is for manufacturers to get vehicles to get exceptionally good gas mileage. My buddy had a new Ford F-150 and was irate that he wasn’t getting the gas mileage reported by Ford. He was jealous my Tacoma was doing better. But, I’ve noticed that to get 18-20 mpg per tank I gotta be super skinny on the pedal. One trip to work where I throw my foot into it takes my mpg to 16-17. So, oversized tires are gonna be a game changer.

 

Funny how people think they should get the MPG estimate on the sticker no matter what their driving style is. All one has to do is research how the estimates are arrived at and then compare to how they actually drive. Also, one should keep in mind that any mods to suspension and wheels/tires will reduce their mpg.

 

I wrote an article about it.

On another note, my 5.7 new Tundra is getting 17.5 mpg so far.

 

I lost a couple MPG when I went from my stock 245/75/-16 tires to Toyo Open Country AT 265/65-17 tires. Tire dudes said they aired them up to 36 psi, but the TPMS always showed around 32 psi.

I drove south today about a 250 mile round trip, last night I aired all my tires up to 38 psi...tires says 44 max. I was pleasantly surprised. I can live with this.

 

Nice I’ll have to air up, a little more harsh ride but it’s worth the mpg

 

I run my Toyo open country at2 SL at 30 cold and I get @ 20 mpg on my 25 minute work commute and some around town driving. 36 lbs is too much.

 

Why's that?

 

Too much air, will wear the center out quicker, harsher ride. The truck calls for 29 cold on a 265/65/17 so with a 265/70/17 I run 30 cold to allow for the slightly larger tire. Plus I have seen 5 pounds on increase on a hot day taking a 35 lb filled tire cold to over 40 lbs. I use nitrogen that my air pressure doesn't fluctuate but only a few pounds unlike regular air which fluctuates all over.

 

On my 19 sport, door says 29lbs, but I run 33. Why is the Tacoma rated to such low pressure tires. Would I pickup better mileage if I went up to standard 36 with most Vehicles. Also How much regular air can I put into the factory filled tires without hurting the chemical filled tires.

 

My stock Sport DCSB MT with the OEM Toyos, front air dam, and tonno cover I was getting up to 22's to 24's in the summer... Winter 22's pretty consistently, maybe a bit less. Now, I have KO2-bros 267-70 R-17, no air damn and on winter gas, I am getting high 18's to low 19's. I think your tires are the answer....

 

Congrats on the new truck.

And the mpg lol.