Letting the fuel level get low in the tank...Bad?

[el ess A]

Systems are designed and tested in so many different ways by manufacturers that in some instances, you would never experience some of those situations in real life. The warning light is there for a reason. The setpoint is set at a specific point for a reason. The GM engineers figured all this out for us, so we wouldn't have to.

Don't know about the rest of y'all, but my wife (who is not even close to worrying about car maintenance or understanding how everything works on a car) drives the 2010 around periodically and I can guarantee you she wouldn't think twice about running the fuel low enough to "trip the alarm", let alone check the oil during a gas stop. THAT is the main reason the warning system is there. For drivers like her. Most of us here do worry about that stuff and normally wouldn't let the tank get less than 1/4 at most. There are some that just don't.

While true that the prudent thing to do is not run it down to the light every time is a bad habit, doing so should not typically cause issues on a stock system. If you modify it, all bets are off.

Generally speaking, Tim Allen might have been right when he said his mom told him that the only reason men are alive is for lawn care and vehicle maintenance.

[el ess A]

Also a point of letting gas sit. It's never a good idea to do so. Although our systems are "sealed" per se, there will be air in the gas tank unless it's slap full. Ethanol fuels actually do absorb a bit of water so light water contamination shouldn't be much of an issue if you drive your car on a regular basis.

According to some NREL (national renewable energy labs) reports, E-10 blended fuel will start to "turn" in about 3-6 months give or take, depending on storage conditions. Our tanks are plastic, and the system is closed, so theoretically, it's about the best conditions you can have. Non-ethanol fuels actually can last twice as long. Air and moisture exposure is the biggest concern. And most of us don't store gasoline in "perfect" conditions, so there's that.

Phase separation isn't a huge issue for our cars. If you leave the cap off or run it in systems that are vented, you really open up a can of worms on fuel storage.

Even if you drive your car sparingly, but run the fuel down and refuel with some fresh fuel, it can stretch the life of the fuel in the tank some. And if you DO decide to drive sparingly, it's best to keep the tank full and add some fuel stabilizer as a bit of insurance.

The "best" medicine IMO, though, is to go drive the wheels off of your car and keep buying new fuel.

[Parts Peddler]

Originally Posted by econ

What would you say to the theory that since the fuel pump draws from the bottom of the fuel tank and debris/water being heavier than the gas causes the debris/water to settle towards the bottom, the fuel pump will pick up an equal amount of debris/water with a full tank as it would with a near empty tank?

A good way to illustrate this is to get a glass of water and a straw. The straw representing the fuel pump pick up, which sits at the bottom of the fuel tank. Drop a pinch of debris into the water. It sinks to the bottom, right where the straw picks it up, regardless of how much water is in the glass. If someone could invent a "floating" fuel pump, fuel could be drawn from the top of the tank, virtually eliminating water and debris from being drawn into the pump.