How do different brand gasolines affect your MPG?

2018 Sport Hatch 6MT Ktuned since Jan 18. The beauty of having Ktuned is that it did not impact the cars MPG. I run 93 Octane and regularly get 28/29MPG around suburbs and 38-40 MPG highway. I usually fill up at Wawa (a local gas/convenience store) or Costco never with any impact on MPG. However, every time I have gone to Sunoco my MPG drops dramatically (3 to 4 MPG). At first I thought maybe it was that particular location but I have filled up across the local region with the same effect.Has anyone experienced brand MPG differentials. Would love to know why this happens.

I'm currently running this experiment by filling at each top tier brand name station, 10 times. I'm filling at random station locations. Not the same location for 10 times I'm done with my Shell and Chevron run and about to go for either 75, Arco, or Mobi as the next station. So far my results say there isn't any difference in average MPG, but I can't make a conclusion until I get the third station completed to do a one way ANOVA test. I live in the Los Angeles area. My results are for my region. They should be similar throughout the United States.

What I am not able to test is the claim of the gas brand's ability to help keep engines clean.

Besides the actual ethanol content, there is no reason for any noticeable gas mileage differences between brands of E10 gasoline. Except maybe they can use different nozzles or set their nozzles differently, so they may fill the tank more or less full.

The only stations to avoid are ones not frequented by customers. Temperature (time of day) can impact how much of a fill you get too.

If no price difference and you have no brand preference... Sunoco may be preferable because they use the same additive package on all their fuel grades. Any top-tier fuel should be equivalent otherwise.

I get my best mileage using Chevron gas. But I alternate between Chevron and Shell every other month.

I don’t have many options where I live. It’s Shell or grocery-store gas unless I go out of my way.

I run Shell 93 almost exclusively, the car runs smoother on it as opposed to the grocery store, and it feels like it has more power. I can’t say I’ve noticed a significant difference in gas mileage however, but I’m not a very “economical” driver.

Ive been told that Pilot and Sunoco use runoff gas or left over and it can have trace amounts of non-additive/non-gas such as minor amounts of water, I know for a fact while Pilot and sunoco are cheaper at times they do in fact have lower gas mileage because of this i have conducted a similar experiment in Knoville TN when i lived there for 3 years this was also seconded by locals and coworkers

ThorSellsCars said:

Ive been told that Pilot and Sunoco use runoff gas or left over and it can have trace amounts of non-additive/non-gas such as minor amounts of water, I know for a fact while Pilot and sunoco are cheaper at times they do in fact have lower gas mileage because of this i have conducted a similar experiment in Knoville TN when i lived there for 3 years this was also seconded by locals and coworkers

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What is the "runoff gas or leftover" that they use?

Gruber said:

Besides the actual ethanol content, there is no reason for any noticeable gas mileage differences between brands of E10 gasoline. Except maybe they can use different nozzles or set their nozzles differently, so they may fill the tank more or less full.

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and my understanding is the way most stations raise the octane level is by increasing the ethanol content, so a 93 Octane Premium is gonna be closer to that 10% Ethanol then say an 87 Octane.

To the OP, you are introducing too many variables into your equation, you not only want to use the same station but preferably the same pump for each fillup and you toss out the number of the first fillup at each new station/brand because you need to adjust to that pumps shutoff point, you also want the same time of day/weather conditions if possible and NEED to drive the same routes, ANY deviation on routes can have a MASSIVE impact on that tanks average MPG, like 10% maybe more.

As for gasoline, I can't speak how it works in the rest of the country but for the most part you have your main Gasoline Pipelines, these lines carry fuel from refineries on the Gulf Coast of Texas (and some other locations) out across the country, once the gas reaches a distribution hub the different brands ad there own additive packages that are added in addition to the government required detergents and cleaners (I believe this is also when the ethanol mixing is done to achieve the different Octane ratings) and from there all the brands of gas come from that same "mixing facility" to their respective fuel stations, so everyone gets the same base fuel starting point, but some brands may have a higher ethanol content or a different additive package that can have small effects on fuel mileage because the more ethanol the less potential energy exists per gallon since ethanol is about 30% less energy per density then gasoline, but even mathematically you are capped at like 3-4% less energy per gallon going from a full 10% by volume Ethanol mix to an Ethanol Free gasoline.

Gruber said:

What is the "runoff gas or leftover" that they use?

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from what i understand they buy leftover gas from gas stations and less then quality stuff thats like lets say shell is 100% quality they buy the stuff that didnt pass the bench mark its still fine and runs its just not up to the benchmark at least this is what i was told by master mechanics at peterbilt who spoke to drivers about it. It could be a perpetuated myth but i know i got less mpg from sunoco and pilot, however sunoco in that region is one of the last remaining places you can get 100% gas

ThorSellsCars said:

from what i understand they buy leftover gas from gas stations and less then quality stuff thats like lets say shell is 100% quality they buy the stuff that didnt pass the bench mark its still fine and runs its just not up to the benchmark at least this is what i was told by master mechanics at peterbilt who spoke to drivers about it. It could be a perpetuated myth but i know i got less mpg from sunoco and pilot, however sunoco in that region is one of the last remaining places you can get 100% gas

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Stations with signs saying "no ethanol" usually price higher (more energy content so some worth) and get less traffic. Stations with tanks getting filled and drained less frequently will pump gas of lesser quality. This has nothing to do with a brand's practices.
That is such myth. How would a station have "leftovers?" Have you ever seen a non-decommed station getting contents removed? 100% FUDD you are spreading!
If it's not, then there is ground newspaper in Wendy's Frosty and we all have hairy palms.

Gruber said:

What is the "runoff gas or leftover" that they use?

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Whatever BS fits the bias

Never really notice. I've filled up at Shell, Chevron, QT, Walmart, Tom Thumb, Valero, etc... So far, mpg has been pretty consistent.

Well, without an actual proof such gossip is not of much value, because both Pilot and Sunoco have a lot of enemies which any quick internet search will show. Right or wrong, I would expect there being incentives for many people from various groups and lobbies to be interested in knocking them.

IronFusion said:

Stations with signs saying "no ethanol" usually price higher (more energy content so some worth) and get less traffic. Stations with tanks getting filled and drained less frequently will pump gas of lesser quality. This has nothing to do with a brand's practices.
That is such myth. How would a station have "leftovers?" Have you ever seen a non-decommed station getting contents removed? 100% FUDD you are spreading!
If it's not, then there is ground newspaper in Wendy's Frosty and we all have hairy palms.

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Not FUDD i was spreading it was information i was told and i was sharing i stated It could be a perpetuated myth