Strange MPG readings, advice welcomed.

You can check my fuelly in my signature, but I'm getting between 15-17 MPG. It's a 2013 DCSB 2.7 pre-runner. 65000 miles. I was getting decent MPG (19ish) when I got the thing, but it's tanked since. Is this normal? My driving habits have changed, but I am not sure if it warrants the 15-17. I have just over 1 mile to my work. I drive there, drive home for lunch, back to work, then home. That's the only thing I can think of that may cause this. 4 miles a day (give or take if I stop somewhere on the way home). I'm thinking of taking it to my local shop to get it looked it. I got new tires and they did an alignment and it looks fine. New filter, oil changes, new spark plugs, not sure what I should do next. Any thoughts?

 

1-2 miles per trip is very low. That's most likely your issue.

Short trips are terrible for fuel mileage as the engine is spending most of that time just getting up to operating temp. While cold your ECU runs what's called open-loop, and it's ignoring the O2 sensors, operating on preprogrammed fuel maps and running on the rich side until your engine, cats, and sensors are hot enough to go closed-loop and fine-tune your fuel trims for efficiency.

Assuming you started these shorter trips around Oct 2023 according to your graph? With some longer trips in Dec, Jan, Feb? If so, that's why your averages tanked, because the majority of drive time is in this warm-up state with little chance to average back out with normal MPG.

I used to have like a 0.5 mile drive to/from work, in the winter the needle barely came off the Cold peg unless I give it a few minutes to warm up. Which I tried to do often. Balancing between idling being not-great for engines, but also driving and shutting down while the oil hasn't had a chance to fully heat up condenses a ton of moisture in the crankcase. I'm guessing your oil filler cap has a bunch of frothy goo on it; that's from that moisture.

Make sure to take it on a substantial drive often to cook off all that water and the engine will be happier for it.

 

Definitely the short trips. During warmup the engine runs richer and burns significantly more fuel at idle, too.

I'd be thinking about biking with that kind of commute, that's pretty nice.

Agree 100% with Rise: go take that baby on a 30 min to 1 hour highway drive at least once a month, or you will likely have issues down the road. I'm guessing you never even get up to normal temp in the drives you're doing now.

 

Agree with short trips being a killer.

And the new tires. Type? Different than the last set at all?

 

I'd say at least once or twice a week with trips that short and that frequent. Doesn't have to be an hour, but at least 20-30mins to get the engine up to full operating temp.

The cats are a separate concern. The taco's cats are very robust but will definitely clog up quicker running so cold and rich most of the time. For that, you definitely want a good highway run at least 2-3x a month to bake off all the carbon/buildup and prolong their lives

And agreed, for that short of a distance, bicycling to work is not a bad idea. I did it myself for a while, saved a bunch on gas and got a free weight reduction lol

 

Heck, I would walk to work if I lived a mile away.

 

A appreciate all the replies and great info, it makes sense. The tires are just Yoko Street tires, when I bought the truck it had some chinese tires on it. Right in October I moved to my new home which is the short drive. So that solves that. I was just thinking maybe it was coincidental, obviously it is not. Thankfully I visit family 2 to 3 times a month, about 40 minutes away, and my wife and I take the truck on the weekends for trips outside of the city. I would walk, but the road to work is a 45 with nutcase drivers on it and I would surely get hit. Maybe I'll buy an e-bike and take the backroads! Thanks all.