Why did my MPG go down

Thanks for the replies. I know 18mpg isn't bad for some, but it's a drop from what was normal for me with the mods so I was hoping to see if there might be a reason.

I dropped a new air filter in last night so we'll see if it makes any difference. Would be nice if that was the reason. Probably a combination of things like plugs too.

 

You're not going to see a difference in mpg with the air filter replacement itself, unless you're traveling in an unusually dirty environment.
Factory filters have a lot of real estate. I don't assume the old one looked too bad, did it?

 

That's such a small margin in the grand scheme of things I see such a varied fuel economy based on environmental factors day to day. Are you calculating in the oversized tires for actual distance traveled? Even after my tune adjustment found mine to still be out. What distance are you basing this consistent drop over? How many tanks? Same route everytime? Same wind conditions? Rain? Temperature? Cruise used constantly for the most repeatable driving habit?

 

You're not going to see a difference in mpg with the air filter replacement itself, unless you're traveling in an unusually dirty environment.
Factory filters have a lot of real estate. I don't assume the old one looked too bad, did it?

Edit to note: I'd bet a stack of hundred dollar bills against a PBR, that even approaching 100K, new plugs in conjunction with the air filter isn't going to up your mpg by 10% either.

 

I think its worth saying, because so many including myself convince themselves otherwise:
Every mod you added affected your mpg negatively.

You (I) can convince yourself that certain mods made no difference when you added them, but reality is you probably hypermiled your truck and drove a little more conservatively to justify that claim. For example, I averaged 22-23 mpg in my stock truck. I added bed rack/RTT/awning/bigger AT tires, lights, etc, and I could still get 21-22 mpg. The only difference was, I was driving a little more conservatively to do so. I later ditched the bed rack, got a camper shell, added roof racks, pelican case, lifted, skids, sliders, tune etc. Even after all these mods, I could still get about 18.5-19.5mpg tank average on the same commute. The only difference now, I was driving 65mph down the interstate instead of 73-78mph.

We tend to change our driving habits to adapt to these negative impacts mods take on our trucks. We all know these trucks hate 6th gear, and don't like even 5th gear most the time either. Its the whole reason we tuned, and we loved the tunes, but then we drove on them for a year or more and figured out the truck still sucks at being efficient with mods, it just sucks a little less with the tune. We eventually settle into a place where the truck is comfortable (its comfortable for us while driving), and thats not always the most efficient driving style. If you're not uncomfortably hypermiling your truck to try and still get 20mpg, it makes sense you'd settle into a more comfortable drive and net a little less. This has been my experience at least, and I'll be bold enough to say I've lied to myself about it for a long time, trying to justify that "my mods" or "the mods I chose" were smarter than others, when in reality, nearly every mod out there negatively impacts your gas mileage, and I'm not special. I drove like a grandpa to be cool enough to say I still got 20mpg with a lifted/offroad/RTT totin' truck.

 

Weight. I removed the stupid useless plastic crap and put on steel front/rear bumpers and suddenly was getting much lower MPG. Went down a bit more when I added a Diamondback HD tonneau cover and full armor underneath plus sliders.

LOL.

 

Go ahead and change the air filter if it hasn't been changed in the last 25,000 miles. When I got my truck the engine air filter (Toyota) had about 45k on it per previous owner records. It really didn't appear much worse than the new Toyota filter I replaced it with.

 

I guess my Snugtop Rebel is light because I didn’t notice an mpg drop with it on.

 

My mileage has gone down because I constantly drive in Sx mode.
My around town driving is either S3 or S4 depending upon the distance between stop lights.

I simply do not want all that constant shifting.
I drive my 1991 5 speed manual and stay in lower gears for the same reason.
I figure all those saved A/T shifts will extend the life of my tranny a bit.

 

Well, it's based on basically years of observations. I started running the larger AT tires in 2019. I had the topper and rock sliders from 2018. So for years after these mods I would regularly get about 380 miles per tank and I would usually fill up needing about 18 gals give or take. Yes, there is variation from day to day and tank to tank but overall I was hovering around the 21 mpg range on average.

As an analogy, if your winter heating bill was on average around $100 per month with variations year to year due to warmer or colder winter but on average around $100 a month and then you notice it's creeped up to $120 or more you might start to wonder what changed. Was it a price jump, do you have leaky windows, etc. I tend to pay attending to these things and when something is out of the norm I want to know why. I've actually been looking into this for about a year now and I wasn't coming up with anything. Maybe it's the filter, plugs, or gremlins. Time will tell. My daily MPG was slightly up today so that's at least promising.

 

The old one seemed kind of dusty. I banged it a bit and dust came out. Might not mean anything, but the truck did seem a bit more spry today and my MPG on my commute was up a bit. Maybe placebo or a tail wind so we'll see how the tank to tank average plays out.

Plugs will be next and I'll look into rear diff fluid as well.

 

Now it is lighter therefore faster and better mpgs

 

It's going to take more than a little dust on a filter this size to effect HP so much that a butt dyno can register it.
You're gonna need to look elsewhere for those mpg's and any associated HP losses.

 

My right foot makes mine mileage go down...

 

Have you gained any weight in the past year or so..?

 

Where do you buy your gas out here? I go to maverick & my buddy was all Costco. Well about 3 years ago his tundra started having problems. Come to find out, the shit gas from Costco wasn’t even flammable….

 

I almost always fill up at a Sinclair.

 

Don't have to make shit up..