I fill my tank every Wednesday and Sunday. I drive about 400 miles a week and that splits it in the middle, so it’s about 10 gallons per fill up.
StG
When my warning light comes on, my car switches from telling me how many miles I’ve driven on the tank to telling me how many miles I have left (Distance To Empty). This is usually 20-30 miles. My normal commute is less than two miles each way during the day (I drive to a commuter rail station), so I generally will wait until the coming weekend to fill up, unless I know I’m going to be driving somewhere unusual during the week.
When the warning light comes on -
My commute is 4 miles each way, and I pass 3 gas stations.
Once the light comes one, I’ve got maybe 2 days worth of gas. I’ll stop on my home, or over lunch.
I try to remember to fill it up every pay day (every other Friday) no matter what the gauge reads. I don’t drive a lot and I can usually make it two weeks in between trips to the gas station. If I’m doing more driving for whatever reason, I usually don’t fill up until the warning light comes on.
I used to fill it at 1/2 a tank, because I used to like to get a car wash every week or so.
Then Costco got a gas station, and I gave up on the car washes, so now I just do it when it flashes me.
I usually fill it up when I’m in the city. Gas prices are lower there.
Don’t like to get it below 2/3rds full, in case of emergency. Never let it go below 1/2.
This. Though for me, “Trips - I fill up at half a tank” is because I never know what kind of traffic I’ll encounter on I-495. Carmageddon (the local snow/traffic nightmare of January '11) taught me that sitting in traffic for seven hours will burn through nearly 1/2 tank of gas (at least, in my old car). All it could take is one big accident for me to be screwed while driving to/from Maryland.
I fill up when I’m in the suburbs. Much cheaper than in the city where I live.
I have Prius, so I start thinking about it when I hit 3/10 and actually do it when it hits 2/10, which still give over 80 miles of driving on 2 - 3 gallons. I change the way I go home slightly to go past one of the cheapest stations around.
I fill at 285 miles or so, whether the light is on or not and regardless of what the gauge reads. I go to the same gas station on the way to work and use the same pump and I get a coffee and maybe a doughnut if the mood strikes me.
I picked 1/2 tank - I try to fill between 1/2 and 1/4, just to be sure I always have a reasonable amount of gas in the car. I don’t want to be one of those people rushing to fill up ahead of an approaching storm system.
I have what I consider to be a really bad habit of not even looking for a gas station until I’ve hit the reserve, that is until the indicator reads ‘0 Miles to Empty’. I’d say, on average, I drive another 10 or so miles after I’ve reached this point.
My gas gauge is unreliable, so I fill up when my trip gauge reads 300 miles. I usually have anywhere from 2 gallons left to fumes by then. Based on some posts in this thread I probably shouldn’t do that, but the car hasn’t broken down yet.
If I’m going out of town though, I’m obsessive about filling up at every rest stop regardless of how much I’ve actually used.
My motorcycle’s gauge is also unreliable, but the warning light still comes on at the right time, so as soon as that turns on I’m headed for a station.
I get wiggy if it gets below 1/2 a tank, especially in the winter.
While I voted ‘1/2 tank’, I usually do more of a ‘somewhere between 1/4 and 1/2 of a tank’. It varies on the time of year. Winter, I try to fill the tank when it hits the 1/2 mark. As mentioned by Misnomer, all it takes is an ill-timed snowfall to really screw things up. That, and my car is light enough that I really do need the extra weight of the gas if it’s icy! (Rear-wheel drive.) Summer, it’s generally when I get closer to 1/4, dependent on gas prices. I’ll wait if I think that the gas prices will drop.
I do my best to not let the tank get really low - it’s a ~17 year old car, and I have no clue what type of crud is lurking in the tank. I don’t want to have that crud sucked through the fuel system and into the engine.
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I’m in Chicago, where there’s never a gas station very far away, so I don’t worry if the light comes on. If the light comes on, I’ve got about 2.5 gallons, according to my manual, and that’ll get me 50 miles even in cold weather (my '03 Subaru Forester gets markedly worse gas mileage in cold weather, which surprised me.)
OTOH, I’m in Chicago, where gas is stupidly expensive, so I try not to need to fill up within the city limits.
Several times a week I’m in the south and/or west suburbs, where gas is cheaper by a good 20c/gal most of the time, so I fill up out there. When do I start thinking about filling up? Around 1/8 of a tank.
Road trips and/or trips where I’m pulling my camper I’ll stop at the closest station after it hits 1/4, or before we leave Indiana. We fill up at the last station in Indiana (going either way), even if we’ve still got 3/4 tank.
Twice a week. Between 1/4 and 1/2
I’m surrounded by gas stations so there’s always somewhere to stop if it gets dangerously low. But usually I drive it down to fumes, my gauge and digital miles-til-empty display are dead-on accurate. I play the grocery store game around here to get a gas discount and will often push it an extra day until I know I’ll have time to shop first and increase my gas discount amount.
Winters I refill around a quarter tank, but with a 3 mile commute even that’s just being extra cautious.
When both our vehicles are about 1/4 tank left we take both to Smiths and fill both at the same time; there’s a $2/gal off promotion right now so we make it work.