Fries A tousled 28-year-old in a mechanic’s shirt and wire-rimmed glasses, Carven is the inventor of the Greasecar Vegetable Fuel Systems, a $795 kit that is fitted under the hoods of diesel cars and trucks and allows them to run on used vegetable oil. Once a vehicle is transformed into a Greasecar, every McDonald’s, Dunkin’ Donuts and neighborhood Chinese restaurant becomes a potential fuel stop. Link.