I referred to the Owners Manual of my 2019 CX-5 GTR (Turbo) and I couldn't find the recommended fuel grade in the Specifications section of the book. And it is not marked on the fuel filler door. I have been filling her up with 87 octane and 88 octane in New Mexico. I had not noticed any issue with the 87 octane and I'm happy with the performance so I will continue to use it. I know I gain mpg and performance with the higher grade but there's a cost difference and it adds up throughout the years. I'm retired so I'm careful with my expenses.

 

Technically speaking, regular fuel has a bit more power per gallon than premium; all else being equal, regular will return better fuel economy. That said, all else is rarely equal; if you are consistently pushing the power envelope, then premium will typically give better fuel economy on a turbocharged engine, however, if you are driving across the flat Great Plains, then regular will have a slight advantage. Regarding New Mexico, it all depends, are you booking it up some steep grades with a heavily loaded car, or are you in some of the flatter areas?

 

I-40 in NM to AZ. Santa Rosa, ABQ, to Gallup, then to Arizona. 87 is currently $2.77 compared to $3.79 for premium. I’ll continue using 87 regular but I will not fill up with 86 in NM. I think 86 is only for Northern NM. CO too has 86 for their lowest grade.

 

Mazda's web site says the CX-5's turbo engine can run on 87 octane fuel, but using 93 octane will give you an additional 23 horsepower (and should yield slightly lower fuel consumption, IMO),

FWIW, I use Shell 93 octane premium exclusively. Premium fuels typically have superior additive packages, which should keep the injectors and intake valves a little cleaner as well.

-K.

 

Marketing bilge, I've been elbow deep in many-many engines which have been run on fuel ranging from the top of the Top-Tier on through bargain basement no-name brands and have yet to see any difference in the cleanliness of the injectors or the intake valves. FWIW, I believe all CX-5 engines are considered direct injection engines, and if I have that correct, no fuel in the world will keep the intake valves clean.

 

Amen to that. I will continue to fill her up with 87. I have proven this on I-44 in MO that the 87 octane gives plenty of power to negotiate the long inclines in MO. But in New Mexico and Colorado, their lowest grade is 86 so I fill her up with 88, their mid-grade.