Can Sugar In the Gas Tank Really Kill Your Engine?

Fuel tank
Sugar in your gas tank won't cause a car breakdown, but water in your gas is likely to strand you. Nick M Do / Getty Images

We've all heard the urban legend that pouring sugar into a car's gas tank will kill the engine. Does the sugar turn into a gooey sludge, gumming up the moving parts or does it caramelize and fill your cylinders with nasty carbon deposits? Is it really the nasty, evil prank it's made out to be?

If the sugar got to the fuel injectors or cylinders, it would be bad business for you and your car, but that would be because any particulate will cause problems, not because of the chemical properties of sugar.

That's why you have a fuel filter.

A Solubility Experiment

Even if sugar (sucrose) could react in an engine, it doesn't dissolve in gasoline, so it can't circulate through the machine. This isn't just a calculated solubility but rather is based on experiment. In 1994, forensics professor John Thornton at the University of California, Berkeley, mixed gasoline with sugar marked with radioactive carbon atoms. He used a centrifuge to spin out the undissolved sugar and measured the radioactivity of the gas to see how much sugar dissolved, This turned out to be less than a teaspoon of sugar per 15 gallons of gas, which isn't enough to cause a problem. If you have less than a full tank of gas at the time it's "sugared", a smaller amount of sucrose will dissolve because there is less solvent.

Sugar is heavier than gas, so it sinks to the bottom of the gas tank and decreases the amount of fuel you can add to the auto.

If you hit a bump and some sugar gets suspended, the fuel filter will catch a small amount. You may need to change the fuel filter more often until the problem clears up, but it's not likely sugar would clog the fuel line. If it's a whole bag of sugar, then you'll want to take the car in and have the gas tank removed and cleaned out, but this is not a difficult task for a mechanic and will run you about $150.

That's not good, but infinitely better than replacing an engine.

What Can Kill Your Engine?

Water in gas will stall a car's engine because it disrupts the combustion process. Gas floats on water (and sugar does dissolve in water), so the fuel line fills water rather than gas, or a mixture of water and gasoline. This doesn't kill the engine, however, and can be cleared up by giving a fuel treatment a few hours to work its chemical magic.

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