A Staff Report from the Straight Dope Science Advisory Board

Does putting sugar in the gas tank wreck a car's engine?

Dear Straight Dope:

Does putting sugar in someone's gas tank ruin their engine? Some also say sand in the gas tank will work, but it seems as though it would simply block the fuel filter.

Having a spat with your sweetie, Al? Any sort of gritty substance put into a fuel tank is going to have an adverse effect on the car's performance. Salt and sugar are probably the most effective, since they do not dissolve in the gas. Sand is less effective because it is heavier and will sink to the bottom of the tank. Of course, it depends on how much sand you are funneling in, you delinquent.

Let's use sugar as an example. There are three basic ways that sugar in the gas tank is going to foul up someone's car. First, as you say, it will clog the fuel filter. Second, what gets through the fuel filter will clog the fuel pump. Finally, what makes it through the fuel filter and the fuel pump will completely foul whatever fuel delivery system your car uses. A carburetor that gets sugar in it is junk; you can strip it down and attempt to rebuild it but you likely will fail - it's a gummy, sticky mess. Your fuel injected vehicle will not fare much better when mucked up with the sticky stuff. This sort of vandalism will result in the car hesitating, losing power, and stalling. And repairs will not be cheap - replacing the fuel filter, dropping and draining the fuel tank, possibly a new carburetor or new fuel injectors. The latter two are very expensive, both in parts and labor.

An interesting side note - in the days before unleaded gasoline, fuel tank intake necks did not have flapper valves, and one way of screwing someone who was going on a long trip over was to roll a few golf balls down the neck into the tank. Once inside, the cover would slowly dissolve in the gas tank, leaving the spagetti-like fine string that wraps the core of a ball to unravel and clog the fuel filter. Now, if you REALLY want to put someone out of commission, sand in the oil fill tube is the ticket. Once the sand gets sucked up by the oil pump, it will score the pistons and the chambers and make the engine scrap. I do not advocate or recommend doing this, as it is extremely illegal and you probably don't want to go to jail. But then again, I don't know you. Here's hoping your interest in this is strictly academic.

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