What Happens if You Put Sugar in a Gas Tank?

For as long as anyone living can recall, long-held grudges and philanderous relationships have triggered retribution in the form of car mischief, or worse, damage. A cup of plain white sugar—or the whole bag—is dumped into the gas tank with the intent of badly disabling the engine. But what does sugar in a gas tank do, really?

The myth of putting sugar in a gas tank

The goal of putting sugar in a gas tank is to cause a major catastrophic event in the engine. At the very least, people assume sugar in the tank will cause frustrating and expensive repairs to the fuel system.

This is based on the assumption that sugar will dissolve in the gasoline. The syrupy sludge will then make its way to the engine, and when exposed to heat, it becomes a charred, gooey mess. That mess hardens in the engine’s intake and combustion chamber crevices, making it seize up. If that theory held true, the repair would be extensive, requiring both a new engine and cleaning or replacing all the fuel system parts from the tank to the engine bay.

The television show Mythbusters and the University of California both dispelled the effects of the prank as myth. Sugar doesn’t dissolve very well in gasoline. In fact, the university experiment found that under a teaspoon of sugar remained suspended in 15 gallons of gas. Virtually all of it settled out.

The myth’s origin isn’t completely clear. Some claim it’s from wartime, where civilians or militia would contaminate enemy vehicles with whatever substances they could get their hands on. The myth could have originated in the 1950s, when sugar granules in the gas could plug up the mechanical fuel pump, preventing it from lifting gas to the engine. But the premise for sugar destroying a motor doesn’t seem to be founded in truth.

What does sugar in a gas tank do, actually?

For the most part, nothing. The granules of sugar settle at the bottom of the tank like any other sediment denser than gasoline. The same thing happens with the particles of dirt that fall into the massive storage tanks at the gas station when they’re being filled.

For sugar bits close to the fuel pump pickup, they could be trapped in the strainer, preventing them from passing into the fuel supply line. In theory, the strainer could be completely blocked, which would restrict fuel flow, but all the myth testing seems to show that’s not a common result. Though the fuel pump could burn out, that’s unlikely.

For the tiny particles that could pass through the strainer and into the fuel pump, they’ll reach their next obstacle: the fuel filter. An extra-fine sugar granule is just over one-hundredth of an inch in size, whereas a typical OEM fuel filter captures particles larger than 40 microns and often even fewer. To save you the calculation, sugar granules are roughly 10 times too large to pass through the fuel filter.

Even if the sugar could pass through the fuel filter by some miracle, or if the filter was bypassed, what would occur when it reached the engine? It could pass through the fuel rail and meet a fuel injector. The pinprick-size holes in the fuel injector tip are also much smaller than a grain of sugar, acting as a final gate to the combustion chamber the granule can’t pass through.

A lot of failures have to occur for sugar to actually get to the engine, much less cause damage there.

What to do if you think there’s sugar in your gas tank

If for some reason you suspect sugar has made its way into your gas tank, what should you do about it?

Although the sugar probably won’t hurt your engine, you should take the situation seriously. Because you don’t know how much was in the tank or if it was the only substance used to contaminate your fuel, logic dictates that you shouldn’t fire up the engine or drive for any length of time.

Instead, consider filing an insurance claim. If your car insurance covers vandalism and there’s proof it occurred, you’re probably going to be covered against any related costs, minus your deductible. Whether it’s an insured issue or not, you should have your car towed to a repair facility, where the tank can be removed and cleaned, the fuel system flushed and the fuel filter replaced. There might be zero damage or it could cost hundreds—or even thousands—of dollars to deal with it all.