It’s a popular trope in fiction featuring clever cops and delinquent children. When someone wants to ruin a car’s engine, they pour sugar into the gas tank. Upon the target entering the vehicle and turning the ignition, it sputters and devolves into a heap.

Is this what is meant by sweet revenge? Does it really work? If so, how?

The theory is that sugar will flow into an engine via the fuel lines and create a syrupy mess that will interfere with the engine’s operation, rendering it useless and relegating the vehicle to the junkyard. But this premise is flawed. A University of California, Berkeley forensics professor named John Thornton conducted an experiment in 1994 in which he tagged sucrose (sugar) with radioactive carbon atoms and mixed it with gasoline. After allowing the sugar to dissolve, he removed any remaining solid particles and then measured the solution's radioactivity, which would indicate its sugar content. Only about a teaspoon of sugar was thoroughly dissolved in the 15-gallon sample. Since it can’t caramelize, it can’t really harm anything. If solid sugar particles made it to the engine, they’d probably be caught by a filter.

The only way sugar could affect a car’s performance was if it clogged the fuel filter or fuel injectors. That might stop a car from running, but those could be cleaned—and so could the gas tank itself, if needed.

Some enterprising people at Project Farm performed a more practical experiment back in 2017, adding sugar to the gas tank of a four-stroke lawnmower engine and then examining the engine to see what kind of catastrophe resulted.

If you were expecting some sort of explosion, you’re going to be disappointed. Most of the sugar remained in the fuel tank of the lawnmower, but some made it to the piston and valves. The sugar became caramelized. It didn’t prevent the engine from starting, but over time, having this muck sticking to everything is likely to cause a problem.

Can it ruin an engine? Unlikely. Could a few granules of sugar get through the filters and cause a problem? Potentially.

If sugar can’t exact vehicular revenge, what could? Maybe water. Since it sits suspended on top of gas, it can get into the fuel line and disrupt combustion. But that wouldn't be a very nice thing to do.

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