Dumb question....if I fill a tank up with 50% 93-octane gas and 50% 87-octane gas

Will that automatically "blend" to a 90-octane gas tank?

I know this sounds stupid, but my car says it "requires" premium gas, but at 91-octane. I generally get premium 93-octane gas at Costco, which is the cheapest in my area, usually by 25-40 cents a gallon (has been more). I wonder if I got something more than half the tank 93-octane, then filled up the rest with 87-octane if it would satisfy the "requirement?"

I have read numerous people with the same car, and have seen all kind of opinions--some say it is fine to run 87-octane, no matter what the manual says. Others say they don't get as good of gas mileage. Others say it hurts the engine in the long run. Others say they're full of you-know-what. Anyway, this isn't a debate on whether I *can* or not--I am going to abide by what it says--my question is solely whether I am in compliance if I "blend" it myself this way?

I can't imagine why it wouldn't work out to an average if you mixed them, unless there are different additives to get to those numbers. In that case the concentrations of such things may matter, falling below some threshold creating a more than linear impact on the reaction.

But if it's not about the additives and different formulas and just a difference in purity or such then one would think that you'd get an average.

But you never know. I still wake up at night in cold sweats over the apparently contradictory nature of the Monty Hall problem in statistics.

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Originally Posted by Darrell KSR

Will that automatically "blend" to a 90-octane gas tank?

I know this sounds stupid, but my car says it "requires" premium gas, but at 91-octane. I generally get premium 93-octane gas at Costco, which is the cheapest in my area, usually by 25-40 cents a gallon (has been more). I wonder if I got something more than half the tank 93-octane, then filled up the rest with 87-octane if it would satisfy the "requirement?"

I have read numerous people with the same car, and have seen all kind of opinions--some say it is fine to run 87-octane, no matter what the manual says. Others say they don't get as good of gas mileage. Others say it hurts the engine in the long run. Others say they're full of you-know-what. Anyway, this isn't a debate on whether I *can* or not--I am going to abide by what it says--my question is solely whether I am in compliance if I "blend" it myself this way?

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From my memory octanes are not quite additive but close enough for what you want. That being said, using a lower octane will not damage your engine. It certaiy might cause worse gas milage if the engine is tuned for higher octane levels. It also might run notably noisier, but this is more rare.

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Originally Posted by CitizenBBN

I can't imagine why it wouldn't work out to an average if you mixed them, unless there are different additives to get to those numbers. In that case the concentrations of such things may matter, falling below some threshold creating a more than linear impact on the reaction.

But if it's not about the additives and different formulas and just a difference in purity or such then one would think that you'd get an average.

But you never know. I still wake up at night in cold sweats over the apparently contradictory nature of the Monty Hall problem in statistics.

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ALWAYS change doors if given the choice lol. It still bothers me too.

OK, thanks. I'll start filling up my tank to obtain that mix. Appreciate it. Will save me about $5-6 every tank.

Your vehicle must use only unleaded gasoline.
Premium unleaded gasoline with an octane rating of 91 (Research Octane
Number 96) or higher required for optimum engine performance. If 91
octane cannot be obtained, you may use unleaded gasoline with an octane
rating as low as 87 (Research Octane Number 91). Use of unleaded gasoline
with an octane rating lower than 91 may result in engine knocking. Persistent
knocking can lead to engine damage and should be corrected by
refueling with higher octane unleaded gasoline.

If the retail location where you buy your fuel has 3 different grades available for purchase, then the middle grade is already being blended for you inside the pump as most retail locations only have 2 storage tanks in the ground, one for the 91 to 93 octane fuel and one for the 87 octane fuel.

Quote:

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Originally Posted by CitizenBBN

I can't imagine why it wouldn't work out to an average if you mixed them, unless there are different additives to get to those numbers. In that case the concentrations of such things may matter, falling below some threshold creating a more than linear impact on the reaction.

But if it's not about the additives and different formulas and just a difference in purity or such then one would think that you'd get an average.

But you never know. I still wake up at night in cold sweats over the apparently contradictory nature of the Monty Hall problem in statistics.

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Always go with the curtain where Carol Merrill is now standing.

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Originally Posted by dan_bgblue

If the retail location where you buy your fuel has 3 different grades available for purchase, then the middle grade is already being blended for you inside the pump as most retail locations only have 2 storage tanks in the ground, one for the 91 to 93 octane fuel and one for the 87 octane fuel.

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Costco only has 87 octane and 93 octane. It's Top Tier gasoline, and the best price in town, though.

Very interesting about the two storage tanks and them blending it themselves. I was unaware of that.

A shame UKfaninCincy isn't around, he would know this one in great detail.

Re the Monty Hall thing, I'm not kidding. That one still gets to me. Somewhere in that I'm sure is the mathematical secret to travel in time and space.

Darrell, have you tried an octane booster in the less expensive gas?

https://www.walmart.com/ip/STP-Octan...-25oz/16817401

Keith, I have not, but I'll look into it. Thanks for the suggestion.