Drop in fuel mileage.

I've got a 2020 Sport garage queen. It's currently got about 5,400 miles. I'm not sure the wipers work yet because it's never even been out in the rain. I installed the Magnuson SC back around the beginning of the year and flashed the Yotawerx Stryker SC tune near the end of August.

After flashing the tune just for grins I thought I would see how many MPGs I could eek out of the truck by driving very conservatively. I was able to get a consistent 19-20 mpgs measured by both the truck computer and hand calculation. I was geeked. I know I'll never see those kind of numbers in real life because it's just too much damn fun to drive with the SC and this new tune but it's nice to know what the truck is capable of if babied.

I then installed colder spark plugs around the middle of October.

Then just a couple of weeks ago as if a switch had been thrown, I thought I noticed a drop in gas mileage so I again filled the tank and went though another round of painstakingly driving like a little old lady going to church.

NOW I can't get anymore than 16-16.5 mpg and the driving is EXACTLY the same as before. I live 10-12 miles out of town so most of the driving was running errands. Ya know, a Home Depot run on a nice day sorta thing.

What the heck?

I can't imagine this can be caused by a sudden change to winter-blend gas can it? Colder plugs?

 

Yes, gas. And temp outside and tons of other driving factors

 

winter blend fuel be the poopoos

 

Well, I'm guessing this may be the time of year the gas is changing but the outside temps have been very consistent and there are not tons of driving factors.

I can only blame it on the gas. Wow, the MPGs were instantly down.

 

Tire pressure too. In the winter your tire pressure drops compared to summer.

 

Again, outside temps were consistent. It's been a nice warm autumn.

 

Hmmm……
I am surprised you managed to get 19-20 mpg with the S/C. I barely hit that granny driving with my bone stock V6.

Did you gain weight? Put on an extra 75 lbs during the summer?

 

The short answer. Shit happens, mpgs are not coming back, and will most likely get worse, nothing to do about it. UNLESS theres a hole in the fuel tank.

 

So was I!! It surprised the heck outta me. I was so tickled at the time I even posted it and the mileage improved after this.

https://www.tacomaworld.com/threads...-and-development.731276/page-42#post-27769672

And I guess I better get out the bathroom scales to be sure. I DID notice my belt was a little tighter. LOL

 

it's still freaking 80 degrees here and it's November. usually it's in the 50's by now. kinda sick of this neverending summer.

 

Were you getting 19/20 mpg at the empty tank refill, factoring in total miles driven on said tank vs gas gallons added or just a moment to moment reading? The latter isn’t a reliable calculation, whether it’s from your truck ECU or your own applicable measurement.

 

Gas or wind would be my guesses. Suspect gas if you did an entire tank over a few different days but, anecdotally, I’ll notice up to 2 mpg difference on highways if the wind is favorable or not

 

I gained 2 mpg downsizing from 285/75 E rated tires to 265/75 P rated tires, and I added a 1 inch block to the rear to lower nose rake stance. I went from 16-17 mpg to 19-20 mpg. To confirm, I use the gas-buddy application for manual computations. I also have a Hypertech module installed behind instrument cluster, updated to compensate for tire size changes. Truck mpg readings are within .5 - 1 mpg of manual calculations. I expect now that it’s getting colder and the gas blends will change, those numbers will change.

 

Im unfamiliar with both of those mods. Did the hypertech module require a dash pull? Suspension and tires are on the 12 month horizon or beyond for my build, but super interested in keeping my gauges reading correctly so trying to learn my options now.

 

Winter blend starts mid October and you lose around 10 percent on average.

 

I had to take the instrument cluster off after programming the module on a computer. The application allows you to put factory tires sizes in and then put the new tire sizes in and it saves it into the module. Then this module plugs in the cluster cable as a bypass, you need to check carefully to make sure that they have one for your year of truck. Mine is a 2017. After I installed the module, I checked with my phone GPS and the mileage speed was right on.

 

Most of the time to achieve optimal results with a colder plug, youd need to lean it out and advance the timing a little. At least thats how its always worked on my carbs.
But with your hotter tune, Id imagine your probly running richer than you were before and the cold plug exacerbates that cuz its not burning all the fuel. So the ECU/tune calls for more fuel.
That combined with winter blend could be the culprit. Although, Im upper midwest, not as north as you, but I havent seen much of a drop cuz of winter blend yet. Id go back to the hotter plug.
Fwiw, I know very little about ECU tuning...almost nothing. Im going off of my experience working with tuning carbs on older vehicles. So my theory might not mean jack...

 

Yep, miles divided by gallons and the computer was very close to that also.

 

This makes sense to me, and the timing is about right too.

I guess I'll wait and see what it does in the spring.

 

Gas usually causes wind