It WILL disable the automobile. Based on my experience, the sugar crystallizes in the bottom of the tank like rock-candy and clogs the fuel pump pickup.Urban legend sugar wont damage and engine because it don't dissolve in gasoline, and what does get through will be caught by the fuel filter
I worked at a Ford dealer in Brooklyn and we got at least one or two cars that had been sabotaged a week. Usually by stupid Caribbean people who are arguing over parking spaces on their block. They tend to believe the space(on the street) in front of their house belongs to them. The repair is usually a new fuel pump and filter and a new tank and locking gas cap.
I say set the dudes car on fire. He wouldnt know if it was sabotage or a electrical defect.
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