Is driving your car with less than a quarter tank of fuel harmful to the engine? This seems unlikely; I need the SD.
I believe the argument was always that once you got to a low-fuel situation, sloshing in the tank would mean any accumulated sediment would be more likely to come through the fuel line, but modern cars have filters for this, don’t they?
Driving with an almost empty tank makes the fuel pump work harder, and can shorten it’s life-span.
This (sediment is not the issue). Less than a quarter tank is not the threshhold, low enough for the pump to suck vapor instead of liquid is (probably around 95% empty). Some fuel pumps are very sensitive to this, and there are cases of pumps being damaged by running out of gas. Note that the damage is to the fuel pump, not to the engine.
Modern fuel pumps also sit in the gas tank and are cooled by the immersion in gasoline.
Exactly as told by Click and Clack
At least some fuel pump designs are are cooled by the fuel they pump. And in many vehicles you need to remove the fuel tank to change the fuel pump, so it’s not a cheap and easy replacement.
The fuel pump in my dad’s 2000 Grand Prix cost over $900 to replace.
I would guess that the quarter of a tank mark is mentioned because it’s an easy-to-spot line of demarcation common to all fuel gauges. It’s a pretty wide safety margin, but sometimes that’s a good thing.
I have also heard that it’s a bad idea in cold climates as the condensation that can accumulate in the tank dilutes the fuel more the less you have in the tank. IOW, an near-empty tank has more air in it for water vapour to condense out of and less fuel in the tank means that the remaining fuel will be more diluted than if the tank had been fuller. Is this true?
Could this be a possible explanation on why the last several vehicles I’ve owned have all reported a nearly empty (or empty) tank including the “Low Fuel” warning light coming on, when there was at least 1-2.5 gal left in the tank, based on the listed volume of the tank vs. how much fuel they accepted when filled to “Full”???
My experience is similar to yours. I have a device called a Dashhawk in my Mazdaspeed3, it lets me monitor many of the values the the cars computer knows, such as RPM, vacuum/boost, and fuel level. My car seems to turn on the low fuel light when I have 10% left, which would be about 1.4 gallons.
So when my fuel light goes off, I shouldn’t play my game of seeing how many more trips back and forth to work I can take before losing my nerve and refilling?
BMW motorcycles (at least the new generation boxers) are said to be quite sensitive to running out of fuel. It’s supposed to be really bad for the fuel pump. To replace the pump, the tank has to be removed. Certainly easier than doing it on a car, but no picnic either. Fortunately, it’s never happened to me.
BMW, in their infinite wisdom, saw fit to place the fuel *filter *inside the tank, too. That’s a pain, because filter replacement is a regular maintenance item. I know riders who have replumbed the system so that the filter is external. Makes a lot of sense.
It certainly was in the days before fuel vapor emissions controls. The real problem isn’t dilution of the fuel so much as accumulation of water, which sinks to the bottom – where the pickup is – and can form a block of ice that prevents fuel flow. My observation is that modern systems seldom develop this problem.
An “empty” fuel tank isn’t really empty. The opening for the fuel pickup can’t sit right against the bottom of the tank. There has to be a little room for the gas to flow into it. If you figure there’s 1/2" of liquid left when the pump starts sucking air, across a tank bottom that has an area of 3 square feet, that’s about a gallon right there that the pump can’t really deliver anyway.
If you play the game, you’ll either lose your nerve or lose whatever it ends up costing to have run out of gas. Still wanna play? 
I can see how you’d lose at this game. How do you win?