You risk having condensation in your fuel tank. Condensation needs a surface to adhere to, and having less fuel in a tank allows for a greater surface area for condensation to form. Water in a fuel system, especially diesel, can damage either the fuel system or engine.

Keep in mind the fuel in your tank is probably warmer than the outside temperature when the car is running. The fuel pump, return line, and even exhaust can cause the fuel to warm, even slightly. As the fuel cools down, the warm, moist air in the tank results in condensation. Displacing as much air from the tank, and having a lesser exposed surface area in the tank, lessens the likelihood of condensation forming.

Terry

 

Wow that is great information. I never knew that about cars. Where does this apply? I live in SoCal. It gets cold to like about 60-65 degrees average. Or does this apply to only extreme cold?

 

Condensation is a minor issue for those of us in coastal SoCal where temps are generally moderate.
However, it's also bad to run the fuel tank close to empty due to sediment at the bottom of the tank getting into the car's fuel filter and pump. There is concern that the pump can overheat and fail while trying to deliver fuel from an empty tank.

 

Usually when the light turns on. Even then, I still see how far I can go. I'm lazy like that.

 

i pretty much only fill up when my tank is COMPLETELY empty. always riding it to the last drop. its a BAD habit.

 

once a week.......that is usually around 1/2 or 1/3 tank. fuel pumps are not cheap and they need fuel to cool them off so no need to constantly run them down to E

 

In winter after I hit half tank I usually fill up the next trip out, depending where I'm going, in summer it's when the light comes on.

 

not really it mostly applies once you get below about 45.

 

i try and fill up at 1/4, but i'm too lazy and don't get gas until i get the light.

 

When there's 1/8 to 1/4 tank left. In my life I may have seen the gas light come on a handful of times, tops...

 

Usually when the trip computer says I have about about 50 miles to Empty. That usually happens just before or after the light comes on.

 

1/4-1/8 tank. Especially before a storm or in cold months, I try not to get under 1/4. Also, I don't want to suck up all the sediment crap on the bottom of my tank, so I try not to let it run dry.

 

i really don't believe so many people run it down... the fuel pump requires fuel in order to cool properly, running it past half reduces its cooling capabilities