Everyone,

I was curious what Toyota would say about this, so I emailed their customer service. Below is my question and their response.

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Subject
Optimum Octane for 2018 4Runner

Discussion Thread
Response Via Email (Daniell T.) 01/23/2018 01:34 PM
Dear Mr. Txxx,

Thank you for taking time to contact Toyota Motor Sales, U.S.A., Inc. and congratulations on the purchase of your 2018 Toyota 4Runner!

We appreciate the opportunity to address your inquiry regarding the fuel for the vehicle.

The "Research Octane Number 91" quote refers to the research done by the government. When testing the vehicle, 91 grade octane was used in order to determine the miles per gallon (MPG) ratings for the vehicle. The higher grade the octane level, the better mpg the vehicle will get.

For more information on fuel economy we encourage you to visit: Fuel Economy.

Your email has been documented at our National Headquarters. If we can be of further assistance, please feel free to contact us.

Sincerely,

Daniell T.
Toyota Customer Experience Center

Customer By Web Form (Tyler Txxx) 01/18/2018 07:02 AM
Sir/Ma’am,

The 2018 4Runner owner’s manual states the following: “Select octane rating 87 (Research Octane Number 91) or higher. Use of unleaded gasoline with an octane rating lower than 87 may result in engine knocking. Persistent knocking can lead to engine damage.”

The minimum octane requirement is clear, but what is the optimum octane content for engine performance?

What does “Research Octane Number 91” mean?

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Hope this helps clarify what the manual says.

- Tyler