What octane to use?
- Thread starter skyhawk
- Start date
mountjonas
Member
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- 2013 VRM MS3
the only thing it'll hurt is your wallet. just use the 87.
Actually, a little known fact is that using too high of a octane for too long may also damage your emissions system (catalytic converter). There's no benefit to either gas mileage or performance with using a higher octane.
The brand of gas you use has more of an impact (ie. Shell/Chevron/BP/Exxon vs. Costco/Convenience Store). Yes, all gas comes from the same stock pile, but branded gasoline adds more detergents to keep your engine clean while the bargain brands contain only the minimum EPA requirements to protect the environment.
The brand of gas you use has more of an impact (ie. Shell/Chevron/BP/Exxon vs. Costco/Convenience Store). Yes, all gas comes from the same stock pile, but branded gasoline adds more detergents to keep your engine clean while the bargain brands contain only the minimum EPA requirements to protect the environment.
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- 2008 Mazda5 5MT Sport w/ Popular Package
To me it was an under ~USD$20K car so 87 it is. I have used 87 for my old Honda since new and no trouble so far. Now, take Jandree's gas brand comments into consideration if you want to gain some edge.
paging_drburgos
Member
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- 2017 Mazda CX5 GT - Premium
87 is perfect for this car and anything above 87 would really be a waste of money. Jandree was right about the difference in quality as certain brands (shell, chevron) use better additives although you need to be careful of chevrons that are franchised as they have been known to use "non standard" chervon quality gas. (you'll know what im talking about if you have ever seen a United Oil truck filling up the tanks at a chevron). If i am not mistaken the main difference between 87 and higher octanes is the rate that the gasoline burns (i dont know if it costs more to produce but can only assume it does). The higher the octane the slower it burns and the reason it is used by "higher end" cars is because the slower burn allows the engine to run/sound smoother. Im not a chemist nor an engineer but the above is what i rememered after researching it a few years back. But i did want to correct you on the fact that you said you use it only because the car cost less than 20k. Lets say the manual said that our 5 should use nothing lower than 90 or 91 octane then you should stick to what it says. I had a beemer a while back and since it was older when i purchased it i decided to use 87...well let me tell you that the car wasnt happy at all with it. The engine started to rumble and seemed to be "out of sync", so i immediately switched back and that fixed it. we should always use the octane that the car was engineered to run on.
Have a good weekend guys
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- 2008 Mazda5 5MT Sport w/ Popular Package
Got it. My comment referred to the fact that NEW the Mazda5 costed me less than $20K and 99% of the time brand new cars with that price tag are not designed to use higher than 85 or 87 octanes (I recalled seeing an 85 octanes option in a gas station somewhere).
I agree. I'm sure a 1996 BMW 7 Series could cost me less than $20K nowadays but for sure it will use 93 octanes to say the least (boom06)
This is an extremely common misconception that I, too, used to have. However, there is not a burn rate difference. Higher octane gasoline's higher anti-knock index (octane rating) is a result of the different chemical changes it undergoes during the increasing heat and pressure of the compression stroke. There used to be an absolutely wonderful semi-technical paper on the subject on Chevron's website, but I have not been able to find it for a fair while now. I think it vanished with the site re-design following the Texaco merger.
Either way, 87 is all you need in the 5. In fact, where I live "regular" gas is 85 octane and there is no mpg or performance difference between it and the "mid-grade" 87 here (high altitude).
Engine Design
Some cars are designed for premium fuel use. Most are not, and will actually get worse mileage with higher octane fuel. Turbo-charged cars like the high octane and will actually get better performance numbers with higher octane.
I've seen a few studies on this. Here is a link to one:
http://www.caranddriver.com/features/3604/regular-or-premium.html
Some cars are designed for premium fuel use. Most are not, and will actually get worse mileage with higher octane fuel. Turbo-charged cars like the high octane and will actually get better performance numbers with higher octane.
I've seen a few studies on this. Here is a link to one:
http://www.caranddriver.com/features/3604/regular-or-premium.html
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higher octane is for higher compression and boosted engines... and those running aggressive ignition. An a-typical car like ours is fine on 87 and could actually be losing power and gas mileage with higher octane because the fuel ignites later and could cause damage to expensive emissions components as a result.
Higher octane fuel does not ignite later. See http://www.faqs.org/faqs/autos/gasoline-faq/
Especially Part 3.
Especially Part 3.
when I say later I'm meaning its not going to ignite as easily as 87 octance would in our cars and it wouldn't burnoff quite as well. Our car's compression, ignition timing, etc are tuned for 87 octane as is recommended. anything much higher wouldn't be beneficial and may actually cause loss of power as I've seen dyno results online of octane testing. Higher octane can resist ignition better than lower octane so the way I see it, it is igniting later on a vehicle not tuned for it... maybe fractions of crank angle but just the same.
85
I'm in Denver. We use 85 octane v. 87 here.
FWIW: I've had Saabs that would choke on low-grade 91 here. Some gas stations appear to be watering down the gas.
You may as well flush money down the toilet if you use higher octane fuel in a stock set-up.
That FAQ link was cornfuzin'
I'm in Denver. We use 85 octane v. 87 here.
FWIW: I've had Saabs that would choke on low-grade 91 here. Some gas stations appear to be watering down the gas.
You may as well flush money down the toilet if you use higher octane fuel in a stock set-up.
That FAQ link was cornfuzin'
paging_drburgos
Member
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- 2017 Mazda CX5 GT - Premium
92 octane isnt doing anything positive for your 5. Chevron has good gas no matter which octane. You're better off spending the extra dollar on a lottery ticket
You'll need to use more than one tank before switching. Most tests use 3 tanks of the same grade to get accurate numbers. The ECU will also need time to adjust (if it can).
