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What happens if you mix 87 and 93 gas?
So I may have made a potentially harmful mistake. I usually put "regular gas" or gas labeled as "87" in my car. Just now, though, I added some premium gas labeled "93" into my half-full tank by accident. Should I be worried? What happens if you mix two different kinds of fuel?
Patrick Price · Updated on
Reviewed by Shannon Martin, Licensed Insurance Agent.
It’s always better to be safe than sorry about this kind of thing. As for what happens if you mix 87 and 93 gas, the answer is—not much.
The grade of gas—regular, midgrade, and premium—are descriptions of the octane level in the gasoline. That’s also what those numbers 87 and 93 are measuring. Any gas with an octane level of 91 or higher is premium gas, anything with 89 or 90 is midgrade, and anything below 89 is regular.
Gas with higher octane is better overall for your engine and will result in slightly better performance. However, when you mix two different octane levels, you get their average.
So, if you have exactly half a tank of 87-octane gas and half a tank of 93-octane gas, then you’ve just got a full tank of 90-octane gas.
Adding higher octane gas to an engine designed to use lower octane gas will never be a problem. However, you’ll have performance issues if you add lower-grade gas to an engine that needs premium.
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