Like an idiot, for the last year or so I have been driving my car around on empty or near empty. I heard this is bad. What effects does this have on the car and what type of repairs or maintinence should I have done? (My first guess is a new fuel filter)
Only harmful if the car’s gas tank has accumulated water or sludge in it. If you haven’t noticed the engine “missing” you’ve done no harm at all. If the engine has been doing a lot of missing and sputtering, get the gas tank drained, install a new fuel filter and then continue to run near empty with confidence.
Also, many fuel pumps use the fuel as the lubricant. If you run out of gan and then grind it trying to restart it, you can kill the pump.
The gas not only lubricates, but helps to cool the pump. A fuller gas tank is a larger body of fluid, and a bigger heat sink.
Agreed, from the standpoint of physics, but is a bigger heat sink necessary? Won’t 1/8 or 1/10 of a tank provide sufficient cooling? The manufacturers seem to think so, as I’ve never seen a caution about running around with a low gas level.
I would consider anything below 1/8 to be running the tank low. In the winter, of course, I won’t let it get below 3/4, if I can help it, but that’s because of the slush and sludge. Or perhaps just because my dad told me not to.
In the spring and fall, mostly, air is expelled from the tank as it warms, and drawn into the tank as it cools. If the air being drawn in is high in humidity, water will be condensed out of it as it cools as well. The higher the volume of gasoline in the tank, the smaller the volume of air is, and the less water is there to be precipitated. In the winter, the air is dry, and in the summer it doesn’t get all that cool at night.
A well designed tank will have a deep enough sump below the intake to avoid engine damage in any but extreme cases.
Tris
Wow, do you have to top off every day, then?
I always fill up when I get near a 1/4 tank. For the sole reason that I don’t want to run out of gas.
Anything less than an 1/8 of a tank is asking for trouble. You never know what and when you might need your car for someting important. And the last thing you’re going to want to do is fill up.
YMMV 
I fill up every week, but that still usually means only half a tank gone. But then, I only drive eight miles a day, most days.
Tris
I don’t understand how accumulated sludge or water is mitigated by a fuller tank. Water and sludge sink to the bottom of the tank, so if you pour more fuel on top, it’s still near the fuel intake. I don’t get it.
I think whoever told you driving near empty is bad for your car is full of crap. If it were bad for your car, the makers would either tell you this, or make the unusable portion of the fuel tank bigger.
Now, running the engine all the way out of gas is bad for it and the fuel pump, as has been mentioned. But running near empty, no way is that a problem.
First off I don’t recall ever seeing a gas tank where the pick up wasn’t at the lowest point, so the comment about a well at the bottom of the tank is well wrong. (I’m talking modern cars here; there may well have been a sump on some antique cars when the fuel supply quality was iffy at best)
As far as cooling the pump goes, yes the pump is fuel cooled. But the thought of destroying the pump due to overheating due to a low level in the tank is wrong. The cool fuel is drawn through the pump, picks up some heat from the pump, and then goes to the engine where it is burned. Fresh cool fuel is then drawn into the pump. Lather rinse and repeat. As long as there is any fuel flowing there is adequate fuel to cool the pump. If there is no fuel flowing, the pump stops as the engine is not running.
As far as the humidity claim goes, all I can say is that in over 35 years in the automotive business I have never heard of this from any authoritative source, never seen this in any training material, nor have I heard of it as a war story from another technician. So I am going to need a pretty good cite for this one.
[Hijack] What is the difference between a fairy tale, and a war story? The fairy tale starts Once upon a time, the war story starts Now this is no bullshit.[/hijack]
There is one big problem with the humidity theory; the gas tank on modern cars is not vented to the outside air directly. Any air in or out of the tank has to pass through the charcoal canister(s) on its trip from the outside to the inside of the tank. Maybe wouldn’t stop the water, but would sure as hell slow it down some.
Also don’t forget that a minor amount of water will not hurt an engine.
So why should you not drive your car way low on fuel? Cause you might run out silly. A gas gauge is not a precision instrument. It is at best an educated guess. E does not stand for enough.
Oh and if you do run out, don’t realize it, and then have your car towed to the shop, be prepared to feel like a dolt when this is pointed out to you.
The '85 truck which I owned had dual 20 gallon fuel tanks, and I’d regularly run the front tank empty-soft foot-speed loss-flip tank transfer switch-resume driving. The fuel filter was replaced annually. No other problem noted.