With gas still costing a small fortune, more and more people have been letting their tanks run down to almost empty before filling up. But while doing so might delay the price pain at the pump, it's not so good for cars. In a fuel-injected vehicle, gasoline keeps the fuel pump cool, says John Roeckner, owner of Sundance Auto Service Center in Phoenix. However, when there isn't enough gas in the tank, the fuel pump could overheat, he says. Plus, running low can also lead to a clogged gas filter because "you tend to pick up any sediment that’s on the bottom of the tank a little easier," Roeckner says. Naturally, waiting to fill up the tank can also lead to a major headache: running out of gas. "You’ll be a menace to traffic, obviously, and possibly get hurt by someone running into you," Roeckner says. "I always recommend getting out of the flow of traffic, especially on the freeway. That’s probably the worst place to break down."