Fuel octane mixing/combining

If you use a mixture of half 89 octane and half 93 octane, does it mix and become a whole tank of 91 octane or do I just get 89 or 93 depending on what is injected at that exact instant? My car calls for a minimum of 91. All that is sold around here is 89 and 93. If you just get 89 or 93, can and does the computer detect quickly enough to retard or not for each stroke? I have tried a mix and can’t feel any difference in performance. Can the mix damage the engine if it does not convert to 91 and does not retard quickly enough?

Mixing works fine, that’s how pumps dispense 91, by mixing 89 and 93.

The pumps don’t mix it, the tanker driver does when he delivers the load. “Mid Grade” is a 50-50 mix, regular and premium, dumped in a third tank. At least you HOPE that’s what it is…

It depends on the gas station - remember the Sunoco pumps, with what, 5 grades? Those were mixed, and I’ve read some do the same for mid-grade.

It mixes and becomes 91.

I have always wondered if it mixes well just from pumping the gas or if it needs to slosh around for a bit before it’s fully mixed.

Let’s see? These chemical engineers figured out what additives to add to the gas so the octane level remained a constant? And all of a sudden you want to try to out-engineer all that effort to do what?

I just don’t get it?


The OP doesn’t want to pay for 93 when his or her car requires 91. It sounds like a perfectly reasonable question to me. (How many times do we tell people here not to pay for a higher octane than what the car requires?)

My local station has 5 octanes available. Do you really think they have fix tanks in the ground?

Most stations in my area only have 2 tanks (regular and high-test). The mid grade is mixed from the two. Far cheaper for a station to have 2 tanks then 3 or 5 (like Sunoco and their 5 grades).

Exactly. My 4runner requires 91. No one sells 91 Octane. It’s either 87, 89 or 93. So I mainly use 93 and mix in 89 when I’m down to half a tank. Then the next fillup I put in 93.

Sounds like a lot of trouble to go through to save maybe $2.

everyone else’s 4-runner runs fine on 87…