Sudden Gas Mileage Issue?

I’ve noticed a recent drop in my Tacoma’s gas mileage. I have a 2017 SR5 2wd with the 3.5L v6 in it. I used to average about 20mpg ever since getting AT tires put on it. The last month and a half I’ve been getting 15-16 highway (75mph) and routine drives where I’d usually get 20-23mpg I’ve been struggling to get 19 on a good day.

I thought it might be an old engine filter that was causing it so I went to change it about a month ago. Turns out the mechanic that last changed my oil incorrectly reinstalled the filter when he took it out to check it and badger me about wanting to replace it for me. The locks to close it back up we’re left unlatched and it was left partially open. Could this have damaged my engine? Letting in unfiltered air? I replaced my filter and it did not fix the issue. I have also ran injector cleaner through the engine and it didn’t help either. My tire pressure is good so that isn't an issue either. I have 72k miles on it.

Does anyone know what might be the issue? Spark plugs?

 

Edit: when I say filter I mean air filter

 

A good chance that your MAF is contaminated. Get some MAF / AMM cleaner, read the instructions carefully, and clean it. Hopefully that is it, or it is a bad MAF, because anything beyond that will most likely be ugly.

Your injectors won't get dirty from unfiltered air, but your cylinder walls might not like it.

Good luck.


You'll also want to document the issue with the brainless tech, just in case.

 

I think with heavier AT tires and winter temps and gas, you are right on. Dont think your air filter has anything to do with it.

Im getting very similar mileage in cold temps, a bit better on hwy if going 75, close to 17-17.5. Im running 265/70/17 C Load KO2s.

 

Do you live in a cold weather climate? Winter blend fuel tends to drop fue economy a bit, maybe not as much as you're seeing, but I've seen a 1-2 MPG drop easily on winter blend.

 

It’s the winter fuel blend being used. In summer it will go back up. I never had a truck that I saw such a difference between summer and winter.

no worries your fine.

 

^^- This.

 

Did someone fill it with 5w-30 instead of 5w-20?

 

Folks.

It has been colder for more than the past two months. And, fuel blends are continuously adjusted.

Here in the Seattle area, I noticed a change in the fuel back in October. We've only been below freezing a few times so far.

I think the partially open filter is an issue here.

 

I got 11 mpg’s today

 

I live in Oklahoma and temps are usually between 30 and 50 the last couple months.

 

what could it have harmed and how can it be fixed?

 

I noticed a small change with mpg in November when it started to get colder and now that it's in the 20's even more. Also AT tires usually weigh a little more and take more to turn.

I used to notice the difference more when fuel switched to winter blend when I had a diesel. Also we don't need block heaters unless you are in Canada. That was one thing I don't miss.

 

New, heavier, more aggressive tires = new mpg

 

I got the tires over a year ago and noticed a smaller drop right after getting them. This is a larger more recent drop in fuel economy.

 

Replace your spark plugs. Not to increase your mileage, but because it’s time, and it might increase it in summer.
Use top-tier regular fuel from name brand dealer, and you should never have to run cleaner thru your fuel system/injectors. The injectors may eventually go bad, but after a long useful run.

Air cleaner check, tires check..

 

A bunch of things can cause seasonal gas mileage changes such as air / moisture density, truck idling more more for defrosting and cab warmth, heavier tires or even more debris (snow) in the road.

 

change your gas supplier.

 

Damnit, winter fuel does not affect MPG, nearly as much as winter conditions do. I don't know why everyone thinks it does. Longer engine warm-up times, more fuel to hit 14.7:1 (because of denser (colder) air) and if you are driving thru snow, more rolling resistance, will greatly affect MPG, much more so than just the fuel. The placebo that everyone whines about "winter fuel loss of MPG" is just because of colder temps.