Not surprising given that XTs have always required 91 or higher. If you can find no-ethanol premium you may get even more of an increase. I get a consistent 2 mpg bump on my '23. It runs fine on plain old 87, but like many states in corn country Illinois and Missouri both require no-ethanol fuel to be premium in order to discourage sales.

 

What does the car call for? Where I live in Maryland, premium was 33% more than regular. You could also try alternating between regular and premium.

 

Interesting...
I was on a motorcycle forum where someone made the claim that switching to premium increased their mileage.
The typical response was: "If you need super, use it, but if you don't, it won't make any difference, so it's a waste."

I tried premium as an experiment and got a big bump, not only in mileage, but in engine performance, which was obvious when the engine was approaching redline, the stutter that had been there for years disappeared.

The bike is an air cooled carbureted machine, rated for ~ 38mpg.
I routinely get 50mpg's on the interstate at 75MPH with super, but then I also have highway gearing and a fairing designed with a wind tunnel..

 

Modern knock detection has lowered the need for higher octane fuel and enabled elevated compression. If you can run 87 regular (sea level) and not invoke ignition retard due to knock sensor activity, then you are running at the peak of efficiency and power.

But if under higher heat conditions you regularly trigger knock sensor intervention, then you would definitely benefit from higher octane gasoline.

I've run my AutoEnginuity laptop live, and on some vehicles it's obvious that they would benefit from higher octane in the summer. I had a Toyota Camry that had improved drivability and economy with premium on hot days. My non-turbo Subaru's have not shown such a benefit.

 

I had a Toyota Camry that had improved drivability and economy with premium on hot days. My non-turbo Subaru's have not shown such a benefit.

Nor did my Foz, but my air cooled motorcycle running in 100 degree heat sure does a lot better with super in the tank.
Even on less blistering days, it's obvious in both mpg's and performance that the scoot likes the super sauce.

 

Using the fuel REQUIRED by your engine would definitely be expected to make the engine run better and protect it from detonation. It's a 10.5 compression ratio engine with a turbo on it, for goodness sake. I'd bet the quarter mile times are measurably lower also.

I have tried premium in my regular gas vehicles and it typically makes no difference, but in my 2018 Nissan Murano, which is a regular gas engine, using premium (even half a tank of 93) gives me 2-3 more mpg. There are versions of the VQ35 engine (in the Z car, and Infiniti applications) that do spec premium, so I assume there is some extra timing available in my ECU.

With the $1 price differential, it's rare that I put in premium, but if we were facing a zombie apocalypse, I would definitely fill it with premium for max range

 

Using the fuel REQUIRED by your engine would definitely be expected to make the engine run better and protect it from detonation.

With the $1 price differential, it's rare that I put in premium, but if we were facing a zombie apocalypse, I would definitely fill it with premium for max range

Its not "Required"
Regular is $3.45, + is $3.75, 93 is #4.05
And no, higher octane on a vehicle that is speced for regular does not get better mileage. I saw this on my "old" '22

 

If you own a vehicle that requires premium, and you can't or don't want to put premium in, then you bought the wrong vehicle

 

Excellent point. But I wanted the '18 xt no matter what. After I bought it I just for the heck of it tried just the + and it was still a beast. Did not consider the mpg aspect.

 

Arguing whether premium is "Required" is semantics.

For the XT, regular fuel is an temporary exception only when premium is not available.

If premium is available then that is what you are supposed to use.

 

I use premium on my last trip when I was in BFE and it was 7 buck a gal! I got 20 buck to get me to the next town. Most my rigs get better MPG and at $/M its still less with the added mileage. I have had a few dodge caravans that it was not true with. But 99% of the time it is.

 

The 2014 to 2018 owner's manual says,

Using a gasoline with a lower octane rating can cause persistent and heavy knocking, which can damage the engine.​

For me, destroying a ring land or cracking a spark plug insulator and having ceramic flying around the inside of a cylinder isn't worth saving a few dollars on fuel.

Yes, modern ECU's and knock sensors work well but they have limits and it wasn't always the case. Subaru had lots of problem with detonation in the early FA20DIT equipped WRX's and Forester XT's.

High RPM.. High ambient temperature... Plugs which haven't been changed... Heavily loaded vehicle... Steep hill... Now you're pushing your luck.

People are free to do what they want with their own cars but its an F around and find out situation.

I've never ran mine on anything but premium. Typically Shell V-Power.