Is it really necessary to add a fuel stabilizer like STA-BIL to the fuel tanks of gasoline-powered engines that won’t be used over the winter?
According to Zach Santner, petrochemical engineer with Sunoco, fuel stabilizers help gasoline engines start easily after storage.
“When you’re starting a cold engine,” says Santner, “you need very volatile, very flammable vapors in the combustion chamber to get it to fire. Once the engine is running and warmed up, the heat of the engine vaporizes less-volatile portions of the gasoline and keeps it running.”
The problem is those highly volatile, easily ignited vapors are like the fizz in a bottle of Coke. Every time a bottle of Coke is opened, some of the fizz escapes, until eventually the Coke goes “flat.”
Vented gas tanks lose their flammable “fizz” when they “breathe.” On a warm day, liquid gasoline in a tank expands slightly and gas fumes above the liquid are pushed out into the atmosphere. During a cold night, the liquid gasoline contracts and air is sucked into the tank. Eventually, over a month or two of inhaling and exhaling, the most flammable vapors have escaped to the atmosphere.
So when it’s time to start the small engine after long storage, the first fuel atomized into the combustion chamber isn’t as flammable as you’d like it to be. It runs fine once it’s started because the old fuel burns good after the engine is warmed up enough to volatilize the stale fuel on its own.
REALLY stale gasoline can lead to a secondary problem with small engines stored without fuel stabilizer. In small areas like carburetor needle jets and float bowls, liquid gasoline evaporates away over time. The residue left behind is a gummy, varnish-lacquer that plugs jets and orifices. If a small engine starts hard and then runs poorly, fresh fuel can sometimes flush away that gummy residue.
Sea Foam carb cleaner or other fuel additives can sometimes dissolve those residues, but badly gummed carburetors need disassembly, cleaning and a tank of clean fuel.
So, yes, it’s worth my time in the fall to wander around adding fuel stabilizer to the tanks of my small engines. A few minutes now is better than a few hours cleaning carbs next spring.
