Auto Talk

Running on empty

Maybe the gauge gave a false reading, misleading you into thinking it wasn't time to fill up. Other times, drivers simply forget. Whatever the reason, running out of gas is not only an annoyance. It also can cause damage to your car's systems.

As the fuel supply is exhausted, dirt or sediment that has settled on the bottom of the tank may be sucked into the fuel system, where it can clog filters and fuel lines—or worse, the carburetor or fuel injectors. In addition, running out of gas or driving with very low fuel overworks the fuel pump. This leads to overheating, the formation of gummy residue within the pump and a higher-than-normal amperage draw.

After running your car dry, pouring a few gallons of fuel into an empty tank won't give you an immediate restart. In a car with a mechanical fuel pump, the engine will have to crank for several seconds to prime the fuel lines. A fuel-injected car with an electric pump may require several cranking cycles to restore normal fuel pressure. If the car starts after a few attempts and runs smoothly, you're lucky. If not, you'll need professional assistance.

Diesel vehicles have additional needs after running out of fuel. A special "priming" procedure to get fuel to the pump may be as simple as squeezing a primer bulb under the hood, or it may require the services of a technician—check your owner's manual.

What if your fuel pump has failed? In newer vehicles, replacement can be a labor-intensive and expensive proposition. While there are some significant differences between fuel systems, what typically causes the pump to fail is a problem that's common to all of them: contamination.

Fuel pump contamination is often caused by moisture in the tank, leading to the formation and circulation of rust particles. Fuel pumps have a strainer sock or filter to keep out the worst of the crud, but particles smaller than 70 microns or so can still pass through. Once inside the pump they cause excessive wear. Clogged fuel filters also cause a pump to work harder and overheat.

Depending on your vehicle, particles may also make their way to other filters in the system. For this reason, if your vehicle needs a replacement fuel pump, be sure to ask your repair facility to also check for tank and filter contamination. A good cleaning or replacement may be in order.

A competent repair facility can generally do a fuel volume test, a fuel pressure test (both dead head and operating pressures), and check the condition of both your fuel and your fuel tank. And as a preventive measure, don't wait until the last minute to fill up-your fuel pump will thank you for it.