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My 2016 6 shows to use 87 octane regular unleaded fuel and that most 10% ethanol is ok but my question is, is it better to use the non ethanol 87 octane not just for better gas mileage but to be easier on the engine?
 

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My 2016 6 shows to use 87 octane regular unleaded fuel and that most 10% ethanol is ok but my question is, is it better to use the non ethanol 87 octane not just for better gas mileage but to be easier on the engine?
Non ethanol fuel is better by nearly every metric.
 

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Hard to find regular gas that doesn’t contain any ethanol at least around here in BC. The only ones I see that don’t contain any ethanol is premium grade fuel such Chevron Supreme Plus 94 octane.
 

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Non-ethanol fuel will give you better fuel economy but it's almost-never worth the extra cost, which is typically exorbitant. In a car there's no storage issue as the fuel system and tank is closed-cycle (no outside air access) when shut down, unless your turnover rate is EXTREMELY low (e.g. a tank every six months or something like that.) The issue that arises here is that ethanol is hygroscopic (picks up water vapor from the air) so in a fuel system that has atmospheric air exchange you can run into severe problems with water content and corrosion.

Now in something where that's not true (e.g. marine engines where the tank is vented to the outside air, no charcoal canister closed-circuit system, etc) it's a different story. But this doesn't apply to any car made since the introduction of the first series of emissions controls, which prohibited to-atmosphere tank vents on passenger vehicles. If you have water in your fuel in a modern car it was in the storage tank at the gas station and you pumped it in unknowingly! Indeed if the fuel system is NOT sealed (e.g. you forget to put the cap back on the fill, etc) your check engine light will come in on all modern vehicles as they test the integrity of the vapor recovery system as part of normal operation and an unsealed system will trip a code.

There is no issue with ethanol being "hard" on the engine; before ethanol was put in fuel there was a potential issue with fuel system seals (O-rings and similar) that were not designed for ethanol and could deteriorate severely. This is no longer a factor.
 

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Discussion Starter #6
I think that the 87 octane here in Oklahoma with no ethanol is $2-3 more to fill than 10% ethanol from a low gas light to full tank
 

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BTW last winter I rebuilt the carb of an old snowthrower (think Tecumseh 2-cycle engine here!) that had the old classic diaphragm-pump style carburetor in it. It would not start but had compression and spark, so it had to be fuel.

Took the carb off and disassembled it; the diaphragm literally disintegrated in my fingers. The rubber gasket that sealed it likewise came out in pieces. It was obviously no longer doing any pumping of fuel, thus, no start.

The problem is that while you can get parts for that carb still, believe it or not, nobody is going to spend a nickel re-engineering them out of ethanol-compatible material. So if you put alcohol-laced gas back in the unit the same thing will happen again.

After replacing those soft parts and cleaning the mess up that they left while disintegrating it ran great. 40 year old -- literally 40 year old -- 2-stroke engine. New plug, rebuilt carb, smoked like a chimney as it always did (32:1 mix) but not a thing wrong with it. All of the geartrain components in the unit were METAL, and were in perfectly-good shape as well. Nobody makes anything modern in that sort of fashion any more, of course, and the eco-weenies killed the 2-stroke motors even for something like a snowthrower, but heh -- the person who has it now has one that will likely outlive HIM.

So yeah, ethanol in fuel can be a problem. But not so much in a car made in the last 20 or so years. It's "problem" is that it has less energy in it than straight gasoline, so it's inevitably going to harm fuel economy and there's no way around that. I think it's a crap sop to the corn industry simply on that basis alone, especially now -- the original argument for it was that the higher oxygen content in ethanol helped clean up emissions, and this was certainly true before modern, closed-loop, closed-cycle engines (e.g. throttle-body injected and before.) But it's not true anymore - it does exactly nothing to reduce hydrocarbon emissions in modern port or DI fuel injected engines that run closed-loop with oxygen sensors and catalytic converters and therefore, the argument for it originally has expired.
 

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Hands down, if price is not an issue, and I simply want the very best of the best, what should I run in this car? Ethanol, no ethanol, 87 octane, 93 octane, etc. What is the very best fuel for a stock engine that maximizes performance not caring about cost?
 

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Hands down, if price is not an issue, and I simply want the very best of the best, what should I run in this car? Ethanol, no ethanol, 87 octane, 93 octane, etc. What is the very best fuel for a stock engine that maximizes performance not caring about cost?
In theory the car could do best on 93 octane pure gasoline. In practice there are way too many variables you cannot control.


My suggestion would be make a spreadsheet and track every tank of fuel; brand, ethanol, octane, and take notes.
After 45000 all I can really tell you:
- Best economy has been in June
- Worst was in January (warming up the car)
- Overall best brand has been Shell
- Highest mileage was on Speedway, which is not licensed as a Top Tier fuel
- Sticky brake caliper was dropping my mileage by 3%
- Plugs, wires, and the coil netted less than 2% increase.



Now most of these items are all about me- where/when/how I drive. Your Mileage Will Vary.
 

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Here in Jacksonville there is a place where all of the fuel trucks fill up their tankers. It's all the same gas being pumped into differently branded tanks. To my knowledge, the only difference that could take place is whatever additives the tanks have in them before they fill up.
 

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Hands down, if price is not an issue, and I simply want the very best of the best, what should I run in this car? Ethanol, no ethanol, 87 octane, 93 octane, etc. What is the very best fuel for a stock engine that maximizes performance not caring about cost?
Honestly, if you're not running a Mazdaspeed or Signature 6, it's really not going to matter that much. These are standard 4/6 cylinder NA engines. 87 octane no ethanol from one of the better gas stations is going to be the best, but when I'm driving a regular 4 cylinder car I rarely pay the extra for the no ethanol since the 10% or so increase in fuel economy isn't worth the more than 10% increase in price.

The Mazdaspeed 6's can be super picky, particularly if they are tuned. Mine is unhappy if I use BP gas for some reason, so I stick to Shell 93 octane. The newer Signature 6s and other 2.5T Mazdas will take any gas but will detune itself a bit if you put in regular instead of premium.
 

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Does the ECU not automatically acclimate to 93 octane on the stock tune in this car?

In a different thread I mentioned that in my 2017 Ford Focus (a cheap car), its ECU was designed to adjust and benefit from premium. The owners manual even indicated it and I could tell a huge difference with 93 octane.

Just can't believe it wouldn't benefit in the 6..
 

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It only benefits the turbo cars. The 4 cyl is designed for economy, as far as I know it doesn't have any special tricks like squeezing an extra HP or two by advancing the ignition if it detects premium. Remember, the purpose of higher octane fuel is simply to prevent detonation in high compression applications, it doesn't contain any more power and if an engine isn't going to knock on regular there is zero benefit from premium. I just looked up the 2019 Mazda 6 manual and it specifies that 87 octane is what works best in the car, it makes no mention of using anything else except on the Signature, where you get a bit of a HP bump on premium (and really, if you paid extra for the turbo don't cheap out with regular gas.)

Ford flex fuel cars are a little more diverse and are designed to adjust to whatever gas you put in it. The Ford manual does specifically state that they recommend 91 octane and above on all gas Focus models, but only requires it on the RS. But you can put anything you want in the regular Focus and the ECU will adjust accordingly.
 

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Does the ECU not automatically acclimate to 93 octane on the stock tune in this car?

In a different thread I mentioned that in my 2017 Ford Focus (a cheap car), its ECU was designed to adjust and benefit from premium. The owners manual even indicated it and I could tell a huge difference with 93 octane.
its ECU was designed to adjust and benefit from premium
I would conject that the engine was designed for premium, and the ECU has enough retard-ability to compensate for regular gas.

What the ECU's respond to is engine knock (aka detonation, pinging). The way that they respond to it is to retard the timing and on some vehicles alter the valve timing. These are preventative measures and not performance makers.
 
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