Does Sugar in a Gas Tank Actually Cause Harm?

One of the most popular myths that lives in automotive lore is the old sugar in the gas tank prank. However what actually happens when sugar is added to gas? Does sugar in a gas tank actually cause harm? The short answer is: not much and it's highly unlikely to cause any problems. While it was proved in 1994 that sugar does not dissolve in unleaded gasoline, it is possible that adding sugar to a fuel tank can lead to car trouble – but not as you might think.

Let’s take a few minutes to look at the claims, examine the origins of this tall tale, and explain the process of resolving this problem if it happens to you.

Where did the myth that sugar harms an engine originate?

The myth that if somebody adds sugar to a car’s fuel tank, that it will dissolve, enter the engine and cause an engine to blow up is false. Originally, this gained some legitimacy and traction back in the 1950’s, when people would report that somebody added sugar to the gas tank and they were unable to start the car. The problem is that the trouble starting the car was unrelated to sugar destroying the motor.

Back in the 50’s, fuel pumps were mechanical, and many of them were installed on the bottom of a fuel tank. What would happen is that the sugar would stay in a solid state and turn into a mud like substance. This would clog the fuel pump and cause fuel restriction issues, leading to difficulty starting or running. Eventually, the car owner would take the car to the local shop, the mechanic would drain the gas tank, clean all the sugar “mud” from the tank, the fuel pump and fuel lines, and the problem would be solved. Today’s cars have electronic fuel pumps, but can still fall victim to obstructions, which can cause hard to start problems.

The science that shows what happens when sugar is added to gas

Back in 1994, a forensics professor from the University of California at Berkeley named John Thornton attempted to prove that adding sugar to gasoline was a myth and would not cause an engine to seize or blow up. To prove his theory, he added radioactive carbon atoms that was mixed with sucrose (sugar) and mixed it with unleaded gasoline. He then spun it in a centrifuge to accelerate the dissolving action. He then removed the undissolved particles to measure the liquid radiation levels to determine how much of the sucrose was mixed with the gasoline.

Out of 15 gallons of unleaded gasoline, less than a teaspoonful of sucrose was blended. The conclusion was that sugar does not dissolve in fuel, meaning it does not caramelize and can’t enter the combustion chamber to cause damage. Plus, when you factor in the multiple filters running along today’s modern fuel system, by the time the gasoline did reach the fuel injectors, it would be incredibly clean and free of any sugar.

What should you do if somebody puts sugar in your gas tank?

If you feel as if you’ve fallen victim to the sugar in the gas tank prank, there is likely nothing to be concerned about, but you may wish still wish to exercise caution before attempting to start your car. As we said before, the symptom of having a car hard to start is not because of sugar mixing with gasoline and getting into the engine – it’s due to sugar turning into a mud-like-substance and clogging the fuel pump. If the fuel pump gets clogged, it can burn up or become damaged if it’s not cooled by liquid gasoline.

So, if you suspect that somebody has put gas in your tank, there’s likely nothing to be concerned about. However, to err on the side of caution you may wish to avoid starting your car before having it inspected. Call a tow truck or a mobile mechanic and have them inspect your fuel tank for sugar. If it has sugar, they’ll likely be able to remove it from your tank before causing damage to the fuel pump and fuel system.


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