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Careful at the pump, octane ratings matter!

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On a recent road trip, I noticed a variety of gasoline octane ratings at the pump ranging from 85 to 93 octane. This got me wondering if I was using the right gas for my truck once I went up or down in altitude.

So, what do you use when your truck calls for regular gas yet the lowest octane number changes from 87 to 85 as you climb into the mountains? Confused? I sure was.

Here is what you need to know.

‘Regular’ octane ratings change with altitude

On the road trip, I was driving a 2022 Toyota Tundra with the new 3.5-liter V-6 twin-turbo iForce engine. Per the owners manual, this engine calls for 87 octane, and in Michigan, which is about 600 feet above sea level, this is the lowest octane available for “regular” gas.

In Nebraska where I live, we are about 4,000 feet above sea level, and the lowest octane is 85. So, is 85 OK, or do I need to use 87 regardless?

I reached out to all the automakers for their input on what to do and if their octane recommendations change at altitude.

The official word on octane ratings

One of the best responses to my questioning came from Ford Motor Co. The automaker sent over not just a statement, but a small history lesson on why octane levels at altitude are lower.

Here is their statement:

“The octane rating of the lowest octane grade offered at retail stations can be different in high altitude regions than in other regions. Sometimes it is 85 AKI, sometimes it is 86 AKI, sometimes it is 87 AKI. Regardless of the location, fuel marketers will label this fuel grade “regular.”  Although there may not be a standard octane rating for “regular,” Ford’s octane recommendation in the owner’s manual remains the same (unless driving a vehicle that requires premium-only fuel):  87 (R+M)/2 minimum. Here’s the actual language copied directly from the owner’s guide. Note, the language even includes information relating to the availability of lower octane fuels in high altitude regions.

“Your vehicle operates on regular unleaded gasoline with a minimum pump (R+M)/2 octane rating of 87.  Some fuel stations, particularly those in high altitude areas, offer fuels posted as regular unleaded gasoline with an octane rating below 87. The use of these fuels could result in engine damage that will not be covered by the vehicle warranty. 

“Allowing oil refiners to reduce the octane rating of fuels at higher altitude is a practice carried over from many years ago. It was originally implemented because the octane needs/requirements of older vehicles (think: vehicles with carburetors) was different at higher altitudes/lower temperatures compared to the lower altitudes. However, with today’s modern vehicles that have electronic fuel injection, knock sensors, and other ways to adjust fuel and spark, the octane requirement of vehicles are no longer as sensitive to temperature/altitude changes. However, these low octane fuels continue to be available at retail stations in high-altitude regions.” 

Other brands offered a variety of answers, but all the answers kind of boil down to the same thing.

Ram says it recommends mid-grade 89 in its 5.7-liter V-8 Hemi engines, yet 87 will suffice if 89 is not available.

General Motors says its 2.7-liter and 5.3-liter engines have a minimum octane of 87 while the 6.2-liter has a minimum of 91 octane. GM added it states the octane number in the owner’s manuals because octane ratings change throughout the country.

Toyota says its truck uses 87 octane — or higher — without any changes for altitude.

Finally, Nissan had a more curious answer. The Titan is recommended to use premium fuel for maximum performance. However, when asked about it, Nissan responded with “you can use whatever octane is available in the area, and the engine computer will adjust to the octane of what is being burned at the time.”

Now, Nissan is stating what a lot of truck guys know. It’s just interesting Nissan is the only truck manufacturer to point this out.

The bottom line on octane ratings

Octane ratings matter, and if an automaker tells you to use a specific level, they’re doing it for a reason. Yes, there are some instances where the truck’s computer will adjust based on what is being burned at the time. But you really need to read the owner’s manual for your truck and pay attention to words like “recommended,” “required” and “minimum.” Recommended means you can get away with “whatever is available,” but if there is a required minimum, you could gum up your warranty as well as your engine if you use something lower.

So, the moral of the story: You shouldn’t just say the truck takes “regular gas.” Octane levels matter, regardless of altitude, and that number is what you should be looking for at the pump.

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Tim Esterdahl

Automotive Journalist Tim Esterdahl has been a lover of trucks and SUVs for years. He has covered the industry since 2011 and has pieces in many national magazines and newspapers. In his spare time, he is often found tinkering on his '62 C10 pickup, playing golf, going hunting and hanging out with his wife and kids in Nebraska.

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