2nd Gen Regular v Mid-Grade v Premium Fuel Experiment

Some of you may remember I posted the results of driving one year on regular gas followed by one year driving on premium. Original post can be found here: https://www.tacomaworld.com/threads/regular-v-premium-experiment.310636/

Intro
As a follow-up experiment to the above, I ran one year on mid-grade (octane 89) and recorded all mileage. The reason I record for a full calendar year is I think there are too many variables to cover over a short term trial (seasonal temperature, winter vs summer fuel, E10 vs pure gas).

So once again, here's my non-scientific trial (now encompassing 3 years) to see if octane has a noticeable effect on mpg. Today marked the end of my little hobby/experiment and I've summarized everything below. Enjoy!

Conditions
* Only use E10 regardless of octane as it's been established E10 delivers ≈3-4% less fuel economy than straight gas. [source]
- This was easy as we only have E10 in MA/RI/CT.
* Each trial would run for one calendar year
* My week long road trips in Aug '12, July '14 and Aug '14 would be excluded so as to not skew results. These trips are 12 hours of all highway driving and I consider outliers.
- Resulted in removal of 12 fuel-ups
* Year 1 would be 87 octane, Year 2 would be 91+ octane, Year 3 would be 89 octane
* Miles count toward Year 2 after the first 91+ fill-up. Miles count towards Year 3 after the first 89 fill-up.
* All fuel-ups are recorded in fuelly
* Because winter/summer blends affect mpg, I report out annual/winter/summer mpg. Summer blend is considered to be June 1-Sept 15.

Regular
Year 1 (Octane 87 E10)
Span: Jan 08 2012 - Jan 13 2013 (29 fuel ups)
Miles: 9,413
Gallons: 472.515
MPG: 19.921 (winter: 18.876, summer: 20.17)

Premium
Year 2 (Octane 91+ E10)
Span: Jan 13 2013 - Jan 12 2014 (24 fuel ups)
Miles: 7,528
Gallons: 399.477
MPG: 18.844 (winter: 18.355, summer: 19.67)

Mid-Grade
Year 3 (Octane 89 E10)
Span: May 2 2014 - May 2 2015 (36 fuel ups)
Miles: 11,745
Gallon: 590.781
MPG: 19.881 (winter: 19.311, summer: 21.11)

Conclusion & Science-ish Observations
Octane did not significantly affect mpg, which more or less affirms my conclusion after Year 2. Given my limited understanding of how the pinging sensor and ecu's vvt-i control on the compression stroke is used to increase hp and torque for higher grade fuels, I thought some of that extra hp would increase mpg but findings don't support.

 

Failed to see benefit of the higher priced fuel as related to mpg.

Maybe the additive pkg is better with the mid grade and premium but probably not worth the increased cost.

Appreciate you spending the time and money to do this and sharing with TW.

 

This just confirms everything we have known for years. Unless your engine is designed to take a higher octane fuel there is no benefit to running it.

 

Nice job man. Those that think they are getting better gas mileage with higher octane , well this should put your vodoo thinking to rest.

You'd be surprised how many members on here run premium thinking there is a benefit. In the end just a waste of money with zero benefit.

 

A year of data for each octane should be plenty. I always thought this to be true. Thanks for sharing your findings. Do you have plans to test the E10 vs. pure gas?

 

I would, but all gas sold in MA/RI/CT is E10 so it's not feasible

 

I think with the 1GR-FE's vvt-i there's definitely a benefit running higher octane if you need more hp/torque, which would help with towing or heavy loads. A lot of people use the old adage that a truck's lowest acceptable octane is what you should run because it was true for fixed valve timing in the 1980's before our vehicles became computers on wheels. Remember seeing a pdf somewhere detailing the extra horses with 89+ octane.

But yea, if you're just commuting around town with nothing in tow there's really no benefit and either way no real change in mpg.

 

Nice work. Its like Myth Busters where they take an idea that can be proved/disproved with pen and paper but do an expensive and entertaining experiment for the public. Did you find a sweet redhead to help?

In all seriousness the the OP's post should be a sticky. This comes up all the time,.

 

Excellent, thanks for sharing! Not an unexpected result at all, but the care and detail of your evaluation is refreshing.

I expect some people get spoofed when a higher octane fuel has lower ethanol content, it isn't the octane that made the difference but rather the ethanol. I see you were careful not to be subject to that effect.

Great work!

 

Interesting results. I myself have been using 89E10 since I got my truck last month and was wondering if there was any benefit from a higher grade. Thanks for answering my question!

 

While driving company outfits my buddies and I ran a similar test. The mileage turned out to be a virtual tie. But----the fuel filters clogged on the cheaper fuel and not on the mid and high test outfits. Now that the manufacturers have put the filters in the tank - that might be reason to upgrade the quality a bit.

 

Thanks! I like Myth Busters, but sometimes it reminds me of the Simpsons where they try an idea once and come to a conclusion or abandon the project. And I did find a sweet blonde. Funny story, she borrowed my truck and needed to fill it up but didn't understand why I needed the receipt/mileage/gallons from her. She asked if it was for tax reporting... I responded it was for cool strangers on the internet.

Glad you enjoyed the read. Yea, pretty common in Canada and other states where the premium octanes don't contain ethanol, which would yield higher mpgs. I tried to fill up at the same local gas station which only carries E10 as much as possible just to limit the "quality of gas" possibility (not sure if Shell's fuel additives are actually superior to other stations or if it's all just clever marketing, so I stuck with Cumby's & Mobil)

Glad to help! I personally am running 89E10 now that my experiment is over as I've read of some pinging/pre-detonation issues here on TW with 87E10.

 

Was this was a specific gas station? I ask because my understanding is that all octanes (87, 89, 91, etc) have these additives now, but I'm fairly ignorant on fuel additives.

 

All premium here is pure gas. Others are E10. Running 87 E10, truck feels a more sluggish and engine is louder than on premium - especially now that I'm rolling 33" load range E tires.

Thanks for your efforts and reporting!

 

Thanks for taking the time to run this experiment. There is nothing non-scientific about the work you have done. There are many confounding variables and a perfectly legitimate strategy to mitigate them is to take lots of measurements as you have done.

Along with reporting total miles and total gallons, can you also report the average MPG across all fill-ups for each octane and the standard deviation? Then your (stats nerd) readers will be able to turn your science-ish results into measures of statistical significance.

 

You and your fancy gas......

 

I just finished taking an intro to stats course this past semester and cringed a bit reading this

 

OK major apologies in advance for going extra nerdy on you...

Unfortunately such an analysis might not be very valid. The statistical significance test you would attempt to apply here using a standard deviation from the series of individual fill-up MPG estimates would be based on the assumption that the MPG estimate error for each individual fill-up is a random variable that has no fill-up to fill-up correlation. That is to say, that the randomness of the MPG estimates is due to differences in driving conditions, engine performance and so forth and that the errors from one fill-up's estimate are not systematically correlated or related to another fill-up's error.

That assumption would be wrong though because a major component of individual fill-up MPG estimation errors is in fact the variation in when the gas pump cuts off or the degree to which the driver tops off the tank. Put another way, when you compute the MPG from a fill up (miles driven/gallons put in the tank) you are not in fact measuring the amount of fuel burned. You measure how much you put in the tank which is slightly more or less than how much was burned. However, if you under fill one tank that error will be compensated for in the following tank. Thus tank to tank estimate errors have a strongly correlated component to them and that will reduce the validity of a statistical significance test. Put slightly differently the "random" driving variation errors will average out more slowly than the "systematic" tank top off errors and this will mess up your significance statistic.

There is unfortunately no good way to disentangle the two sources of error from a mean and standard deviation for a set of data, though you could probably do something with the full time series of fill up data. Or you can just accept that the statistical significance test is a bit corrupted by the tank filling error and consider that your statistic (t-stat or whatever) is going to be pessimistic as a result.

Sorry for the nerd diversion...

And thanks again OP!

 

Thanks Ziggy. I appreciate the info.