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Discussion Starter #1
The owners manual advises that 93 octane fuel should be used in the QX60. The Pathfinder manual says to use regular 87 octane fuel. Same motor and trans as the QX60. What's the difference that causes them to require the different octane rating?
 

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When a vehicle manufacturer requires using premium fuel, it is because that particular vehicle’s fuel system is designed to work best with higher octane gas. Using regular gas in an engine that requires premium could void your warranty. That is most likely to happen if using regular causes severe engine knock or pinging (premature ignition of the fuel, also known as detonation) that damages the pistons or other engine parts. Note that this applies only to engines that require premium gas.

Some manufacturers recommend premium gas but say that regular or mid-grade gas can be used instead. They usually warn that using lower-octane gas could reduce performance and fuel economy. When that happens noticeably, or if engine knock occurs, they advise to start using premium.

Here's what the 2020 Owner's manual for the QX60 states:

FUEL RECOMMENDATION:

INFINITI recommends the use of unleaded premium gasoline with an octane rating of at least 91 AKI (Anti-Knock Index) number (Research octane number 96). If unleaded premium gasoline is not available, you may use unleaded regular gasoline with an octane rating of at least 87 AKI number (Research octane number 91), but you may notice a decrease in performance.

CAUTION
Do not use a fuel containing more than 15% ethanol in your vehicle. Your vehicle is not designed to run on a fuel containing more than 15% ethanol. Using a fuel containing more than 15% ethanol in a vehicle not specifically designed for a fuel containing more than 15% ethanol can adversely affect the emission control devices and systems of the vehicle. Damage caused by such fuel is not covered by the INFINITI New Vehicle Limited Warranty. ∙ Do not use fuel that contains the octane booster methylcyclopentadienyl manganese tricarbonyl (MMT). Using fuel containing MMT may adversely affect vehicle performance and vehicle emissions. Not all fuel dispensers are labeled to indicate MMT content, so you may have to consult your gasoline retailer for more details. Note that Federal and California laws prohibit the use ofMMT in reformulated gasoline. ∙ U.S. government regulations require ethanol dispensing pumps to be identified by a small, square, orange and black label with the common abbreviation or the appropriate percentage for that region.

Octane rating tips

Using unleaded gasoline with an octane rating lower than recommended can cause persistent, heavy “spark knock.” (“Spark knock” is a metallic rapping noise.) If severe, this can lead to engine damage. If you detect a persistent heavy spark knock even when using gasoline of the stated octane rating, or if you hear steady spark knock while holding a steady speed on level roads, it is recommended that you have an INFINITI retailer correct the condition. Failure to correct the condition is misuse of the vehicle, for which INFINITI is not responsible.

Incorrect ignition timing may result in spark knock, after-run and/or overheating, which may cause excessive fuel consumption or engine damage. If any of the above symptoms are encountered, have your vehicle checked. It is recommended that you visit an INFINITI retailer.

However, now and then you may notice light spark knock for a short time while accelerating or driving up hills. This is not a cause for concern, because you get the greatest fuel benefit when there is light spark knock for a short time under heavy engine load.

So, you can use regular 87 Octane fuel, but keep an ear out for spark knock while holding a steady speed on level roads...that is indicative of an issue (like too low octane fuel) that can cause engine damage.

You can not use gas with more the 15% ethanol, regardless of the octane rating.
 

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Discussion Starter #3
Hi Rooster, thanks for the very informative reply. I think I will give the 87 octane a try in our '18. If anyone has experience using 87 octane feel free to chime in and let us know how it worked for you.
 

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I've been using 87 octane for the past 9 years without issues. Zero. No MPG or noticeable HP issues.

I'm sure I don't get 100% of designed HP, but I also don't use it.

Also, as Rooster stated, your motor compensates based on available octane.
 

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I buy most of my gas at Costco, and their premium is usually about the same price as regular gas elsewhere, so I treat to the premium. My previous car was a 2013 Maxima SV, and with that car, the idle was smoother with premium versus regular, you could see it and feel it.
 
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