How accurate is the octane rating at the pump ?

Messages
3,931
Location
SW Ohio
Originally Posted by Yah-Tah-Hey
Nebraska periodically test fuel quality at retail outlets. Like most state agencies, probably not much of a deterrent for some shister stations.
In Ohio, the county auditors want to be able to check gas stations for more than just dispensing the proper quantity of fuel, specifically they want to be able to test "quality". In the stories I saw about this though, it was for checking for water, contaminants, etc, not octane. Is water, "dirt", etc a problem ? It could be but I stick to high-volume stations and avoid the shady-looking Marathons, Valeros, and so on (ironically, supposedly "Top Tier" stations).
 
Messages
14,716
Location
Upper Midwest
Originally Posted by atikovi
Yet prices are always posted as $x.xx9
A retailer can price it however they want, it's not the same thing as a reported value from some test. There's no tolerance or repeatability on the price.
 
Messages
921
Location
D/FW Metroplex
Now that most gasoline has some percentage of ethanol mixed in, i don't believe the stated octane rating of any given fillup is as accurate as we'd like it to be. From what i can tell through datalogging WOT runs using the gas i buy, some stations are consistently selling 93 octane which isn't quite 93 octane...closer to 91 from what i can tell with my car and the datalogs it generates. The 89 seems less prone to trouble around here, and i haven't really tested the 87 to any real degree. All gasoline is e10, though its always labeled as having up to 10% ethanol, never more specific than that. I will say some locations/brands rarely give me trouble, and i assume their gas is what it is advertised to be with the octane rating. Those places overwhelmingly tend to be TT fuel places also.
 
Messages
5,269
Location
San Francisco Bay Area
Originally Posted by WyrTwister
I know , in our state , the accuracy ( in gallons ) of the dispensers are certified and supposedly checked . No idea about the octane or % of alcohol .
In California each county has a weights and measures department that's part of their agriculture division (except San Francisco where it's the health dept for some reason). There's a certification sticker posted for each grade of fuel. [Linked Image] I've seen old fashioned gravity feed pumps too. And they get those stickers.
 
Messages
271
Location
Northeast Georgia
In a laboratory, you may find that BP gas is actually a slight higher than advertised octane rating. They use up to 10.25% ethanol in their blends which bumps the overall octane up a smidge. Regular Unleaded at a BP branded store is more likely to spec out at 87.6 octane.
 
Messages
105
Location
ohio
Well it depends what gas station it is. I usually get my gas from Marathon. I get 87 octane, and my engine is really powerful. I went to golf once, and yet again got 87 octane, and my engine wasn't as powerful as marathon, and they were both the same price. Overall just go to different gas stations, use the same octane rating gas, in the same exact car, do not use any fuel system cleaners or anything while doing this experiment. Which ever makes your engine the most powerful, and the most reasonable price just get that one.
 
Messages
4,165
Location
WA
Originally Posted by The_Nuke
Now that most gasoline has some percentage of ethanol mixed in, i don't believe the stated octane rating of any given fillup is as accurate as we'd like it to be.
Not sure i agree with that. Maybe if you're buying from an independent station the likelihood is increased but even still, it's a big no no if they get caught. Having purchased most of my fuel from the family owned 76 station near me for the last 20yrs, I am confident that the additives and octane will meet or exceed the advertised levels. I have known this family that run 2 76 stations for 2 decades and from time to time we talk about weights and measures... and while they don't come out everyday, they do come out and do it unannounced. And from my understanding it's a pretty good fine. Buy your fuel from a busy branded station and the odds of getting ripped off or bad fuel is gonna be a rarity.
 
Messages
271
Location
Northeast Georgia
Branded vs unbranded, Top Tier vs not Top Tier...it all is hauled in the same tankers. It all comes down the same pipelines. If your store says you're buying 87 octane...you're getting NO LESS than what's advertised. Sometimes...you might even get something even higher than what's advertised...but never lower.
 
Messages
3
Location
GA
At one store I operated, the premium tank was so small that it would hardly take the minium amount of fuel we could order. Often once it was full, we dumped the extra premium fuel into the mid grade tank. as a result it was certain the mid grade was higher than 89 octane most of the time. When we remodeled the store, we went two large tanks with pumps that blended the premium and regular to make mid grade. This eliminated the problem of the small premiium tank.
 
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