It’s a common misconception that using a higher-octane fuel in your vehicle will give you better gas mileage. This isn’t necessarily true. The long and short of it is that the RM2 method of octane rating is a rating of resistance to volatility. The higher the octane, the less the fuel wants to burn. They do this to accommodate the high combustion chamber temperatures you see in high performance engines. High performance engines often use high compression or forced induction to create more power. This increased pressure in the combustion chamber equates to heat. This heat can pre-ignite the air fuel mixture in the combustion chamber. This is bad, as it equates to a loss of power and possibly engine damage. On these engines, you use a higher octane fuel to prevent this pre-ignition from happening.
If you use a higher octane fuel in an engine that doesn’t call for it, you’re wasting your money in my opinion. Yes, some premium fuels come with a better additive package, but I don’t think you’ll see much benefit from them in your ordinary non-performance engine. In other words, you likely won’t go any faster and you won’t get better fuel economy when using premium fuel if your vehicle doesn’t call for it.
Conversely, if you run regular low-octane fuel in a vehicle that calls for premium fuel, you’re making a mistake. As stated, you run high-octane fuel to help prevent pre-ignition and misfires. Running low-octane fuel in an engine that calls for high octane will not only compromise power and cause a drop in MPG, but it can also damage your engine in some cases. The takeaway is to put in the fuel the manufacturer calls for and you should be just fine. I hope this video helps clear up any questions you might have about octane.