Why did my MPG go down

When I got my 2017 new it was getting 22-24 mpg in daily driving. I did some upgrades like camper shell, slider, 267/75/16 tires, KDmax tune, rack on the camper shell and a 2" lift. After all that I was still in the 20-21 mpg range.

I'm not sure when it happened, but a year or so ago I noticed I couldn't break 20 mpg any more and most of the time I was hovering around 18mpg. I took the rack off and on summer gas I was edging toward 19mpg but overall I'm down 2-3 mpg and I can't figure out why.

I haven't quite hit 100K yet, but is there any possible mechanical reason for the drop? I do regular oil changes and tire rotations but no other work has been done.

I was thinking may time for new spark plugs but I read there was something weird about the coil or whatever over the plugs. I think my shop said it's an expensive part.

Thanks.

 

Cold temps drop tire pressures and Colorado switches to winter blend fuels.

 

Yeah, but this isn't just a winter thing. I started watching closely about a year ago and all summer long on normal pressure tires (32-34psi) at best I was getting 19mpg and that's after I took the roof rack off. Whereas before I was getting 20-21 with the roof rack on so it seems like something else is the cause.

 

I'd clean the MAF before doing anything else. Seen big gains on second gens just by doing that. Easy and cheap too.

 

Okay im in the same sitch and i believe its a 3 fold issue but im not a mechanic so….grain of salt

old sparkies
Dirty MAF
Dirty throttle body

 

That was the first thing I tried. It made no difference.

I have not done this. It's about time for an oil change so I could look into doing both.

Spark plugs were the main thing I was thinking. I'll have to look into how to clean the throttle body as that was not on my radar. Thanks.

 

18-19 MPGs sounds pretty good for larger tires, fiberglass topper, and a lift.
I am getting 15-18 with the same, but E series AT tires.

 

Are the tires P or LT? All-season, all-terrain, other? Size is only one tire property that affects rolling resistance.

In any case, 18 mpg is what I get on the hiway with Goodyear wrangler P265/70r16 a/ts, a 2” lift, and no chin strap. I drive 65-80 mph.

When I toss on the LT255/85r16 e-load mud terrains, I get 16-17mpg on the hiway adjusting for speedometer error due to tire diameter.

 

They are P rated Wildpeaks. This is my second set so I was running these before when my MPG was better.

18mpg might sound good to some, but this truck literally was getting 20+ mpg in it's current configuration so clearly something else changed or is in need of maintenance.

I looked into the throttle body cleaning and like with the MAF I'm dubious that cleaning it will have any effect, but I guess it can't hurt to try.

 

I’m skeptical you were getting 20 mpg with all-terrain tires, but it’s possible. Are you sure your measurement was accurate? Strong tailwind? Downhill? Different driving habits? How are you measuring fuel economy? The dash or the fuel pump and odometer?

Also note that your tire diameter is causing an error in the speedometer reading.

Note that in almost every thread where an engine doesn’t seem to be running correctly, someone will chime in to clean the throttle body and/or MAF sensor and/or replace the spark plugs. I would take it with a grain of salt.

 

My MPG measurement was calculated based on miles per tank at fill up. I wish I had archived a few more examples, but here are a couple:

Winter-ish


Summer

 

Ok so by the fuel economy readout on the dash, not by the odometer and the gallons readout on the pump.

Many people have suggested that the dash readout is inaccurate. I’ve personally never compared it to anything, because I don’t really care.

 

No, by doing the math. 400.1 miles on the first example tank divided by 18.713 gal = 21.38 mpg

In the second example, 405.6 miles divided by 17.891 gal = 22.67 mpg.

Those are actually pretty close to the computer's math, but I was doing actual math.

 

I think there is likely nothing wrong with your truck, but engine related things that can result in reduced efficiency include:

- low compression
- rich air/fuel mixture
- retarded ignition timing
- simulated Atkin-cycle not engaging
- maybe poor spark plug performance

Troubleshooting most of this is above the pay grade of a novice amateur mechanic.

 

i get 16 max in town with factory tires and nothing in the bed, and me and my xtra large slurpee is the only cargo,
just drive it or go get a ridgeline

 

Thanks. So helpful. Where's the don't be a dick emoji???

 

Did you move?
Are you driving at higher speeds more often?
Have you kept up with maintenance schedules? Old fluids, dry bearings, sticky brakes, etc. can all contribute to dropping MPGs.
It's also getting some miles on it. Things get worn, tolerances change, efficiency goes down.

 

Yeah, I don't think there is anything really wrong with the truck. It drives fine, but something must account for the drop in fuel economy. It's clearly nothing major as I would expect that to cause the check engine light. I guess I'll explore new plugs and see what happens.

 

No, didn't move. Same daily driving as before with 90% being commuting. Brakes were redone not long ago. Regular oil changes but I really don't know if there are any bearing issues or if the rear diff fluid makes much difference.

I suppose it's time for a tune up of some sort so maybe that's it.

 

My 2017 was low 20s when new maybe mid 20's on the freeway if I drove under 70. Now with 60k miles it's always in the mid to upper teens. Regular maintenance has always been done and the only changes are 265/70/16 Toyo open country at3's.
Fresh spark plugs, filters, cleaning the MAF and throttle body does make a difference in performance. I drive with a heavy foot these days as I like to hear the trd catback.

It's hard to say what the issue is if any with your truck OP.