Premium gas lasts longer — myth or fact?

It’s not universally true that premium gas lasts longer than regular gas

Most regular gasoline contains ethanol. But some premium gas also contains ethanol. Ethanol can be used to increase the octane level of fuel. Some gas stations do sell premium fuel with ethanol. So the question of whether premium gas lasts longer than regular comes down to whether the premium gas at that particular gas station contains ethanol. If that premium gas contains ethanol, it has the same shelf life as regular gas with ethanol.

Not all premium gas is ethanol free

Why ethanol shortens the life of regular and premium gas

Ethanol is a water loving chemical. It quickly absorbs any moisture in the air or gas tank. All engine gas tanks are vented to the atmosphere to prevent fuel tank collapse as  you use the fuel. So ambient air is always moving into the tank.

As outside temperatures change, any moisture in the air will condense on the sides of the tank and drop into the fuel. As ethanol absorbs more and more moisture, it reaches a tipping point where the ethanol/water mixture separates from the gasoline and falls to the bottom of the tank. That process is called “phase separation.”

What makes gasoline go bad besides ethanol? See this post

How does the ethanol/water mix affect the engine?

The ethanol/water mix is most harmful to small engines equipped with a carburetor. The metal used in small engine carbs is very susceptible to corrosion from water. And, that’s where the problem comes in. The ethanol/water combination corrodes the metal passages in carburetors, clogging them and preventing fuel deliver. Fortunately, the same ethanol/water mix doesn’t affect fuel injected engines nearly as much, which is why you don’t need to use a fuel stabilizer in your car.

Fuel stabilizer is mandatory for small engines

Fuel stabilizer does several things:
• Slows down oxidation from exposure to air
• Contains a metal deactivator to slow down corrosion of metal parts
• Slows down or prevents “phase separation” of the ethanol from the gasoline

In summary:

• Non-ethanol premium gas lasts longer than regular gas with ethanol

• Not all premium gas is ethanol free. It depends on the gas station and the label on the pump should disclose whether it contains ethanol.

• Aside from the ethanol issue, all gasoline degrades over time. Stale gas was a problem long before anybody ever thought to add ethanol to gas. Stale gas oxidizes and breaks down into gum and varnish. That’s what clogs the passages in carburetors and fuel injectors.

• Don’t store any gasoline longer than 90-days or will start to break down

©, 2022 Rick Muscoplat