Tor Fill or Not to Fill please, answer the question!

A long time ago, I was watching a car show. They recommended the older the car the less fuel you should empty before refilling. The reason is to keep the gunk from fouling the engine. My most beloved insist this is nonsense and it’s fine to run the tank below a quarter of a tank.

Please! Settle this it’s been an bone of contention for 21 years and I’m tired of chewing!

Well as a matter of policy I always fill up at about a half tank, new or old. You never run out that way and there is less air in the tank to create water when the temp drops.

At any rate the fuel pick up in the tank is in the bottom of the tank so regardless of how much fuel is in it, its still drawing fuel from the same place. Plus at that fuel pick up point, there is a sock filter to filter out any debris from the tank. Plus farther up the fuel line is another fuel filter to filter out anything else that might get through the sock filter. So can’t really see it makes any difference.

My suspicion is that it has more to do with older cars with carbs which are much more susceotable to sediment and fouling. Fuel injection tends to be self cleaning and up to a point is more forgiving. Just a thought, subject to change at any point.

Lots of ideas that seem to make some sense really don’t. This is one of those, for the reasons given above. No truth to it, or you’d be seeing older cars stuck by the side of the road with plugged up fuel system. Isn’t happening.

There’s three possible types of “dirt” in the tank:

  1. Stuff sitting at the bottom.
  2. Stuff drifting in the middle.
  3. Stuff floating on top.

#1 and #2 go into the pickup regardless of the fuel level as @Bing explained.
#3 can come into play when the level gets very low, well below 1/4 I think.
Now I’ve never seen anything that floats on gas for a long time.

That sounds like an old mechanic’s tale, mainly because today’s gasoline is cleaner, more highly refined than it used to be, and contains more detergents than it used to.

I wouldn’t worry about it and just fill-up when you need to.

50 years ago the expression “rusted out above the dollar line” was a comment on the owner being a cheapskate. Cars that were seldom used and never filled with gas, only getting $1 worth when running totally dry, would actually rust from the inside out due to water condensation. There was a noticeable line of perforation at what was assumed to be the dollar level. That’s not an urban legend. The rusted tanks were somewhat common. Also, rust accumulated in the tanks and when the fuel level was low the rust had less liquid to be suspended in and would accumulate on the pick up sock and restrict flow. With half a tank the fuel sloshing about would pick up the rust from the bottom when the car was moving and prevent stalling but the gas fumes from seeping out of the perforation was sometimes strong. Those were the “good ole days.”

If ever you had that much gunk in your tank…you’d know it, and it would be time to gat the tank washed out in a shop.

myself, I run around town on the bottom half of a tank full so I don’t have to tote that extra 100 lbs.

Your beloved is right. The fuel pickup is in the bottom of the tank and usually it has some sort of screen or sock filter on it, and there is another filter in the fuel line. I would not suggest running it dry though, especially on a fuel injected vehicle.

The only gas tank I ever had rust out, rusted along the very bottom, not on the “dollar line”. I always filled the tank when it needed gas, but it was a used car so I don’t know what the previous owner did, but if moisture gets into the tank, and the gas sloshes around or it drips into the gas, it goes straight to the bottom of the tank because it is heavier than the gasoline. It was an easy fix though, a bar of ivory hand soap rubbed across the holes stopped it from leaking.

Ken you must have one very big gas tank. Most cars only have a 16 gallon tank or smaller so 8 gallons in the top half at 6.67 pounds per gallon is a lot closer to 50# than 100#. You could delete the spare tire and jack and save almost that much, oh yeah, GM is already doing that on their new cars.

It’s fine to run the level below 1/4 tank…unless you live where that might not get you to an open gas station.

But if your beloved is routinely running the level while the “fill” light is glowing, he/she may cause premature failure of the pump, or might run out of gas in a place that he/she would rathe not be stranded…or in a storm in the middle of the night.

30 gallon tank for me. Can’t even go to fill up without a C note.


Well thank you all very much! I hate being wrong but I’ll eat crow and apologize to the most beloved. I appreciate the help so much!

Oh gosh, I hope everyone knows that wasn’t sarcastic by the way. I really do appreciate the help. The angel in my life wouldn’t dream of running it till the light comes on. It was my dad’s last car, I’d like to make it to 200K miles.

Kind of related to this discussion, I’ve recently run the tank pretty low in my car, a '98 Civic. It’s an 11 gallon tank, and the lowest it’s been was about 0.8 gallons (since, when I filled it, I added about 10.2 gallons). I’m beginning to wonder if the warning light is burned out or of I’ve just never gotten the tank low enough to make it come on.

I never though that you were being sarcastic and it sounds like you are a person willing to listen to reason who may have gotten some bad advice from that car show. Even though running the tank down to a reasonable level and not trying to run on fumes is not doing any harm, I do want to make a case for your side of the debate.

If this is your only car, then just like maintaining a cushion in your checking account, you should also keep a cushion of gas in at least one vehicle you own. What if there were an emergency in the middle of the night and you had to drive 100 miles and the gas stations are all closed?

When I was working, I commuted 100 miles per day. I usually filled up right after the fill light came on. My gas tank was 11.2 gallons and the light came on when it took 9.2 to fill it. On the way to work one morning, the light came on just before I got to work. My plan was to fill it that afternoon before going home. That day was 9-11-2001. Almost every gas station was out of gas by the time I got off work because of panic buying.

Good point @keith Storms can knock power out at any time. Gas stations need power to pump their gas. A town in SW MN has been out of power for about 4 days due to ice storms and we saw what happened in NY with the storms there. You really need to have extra gas for emergencies to be able to drive to another town for motel, gas, chain saw, and so on, or just to keep warm for a while when power is out.

Keith thanks! I’ve apologized and she’s not gloating which is kind of her. Your point is very well taken so I’m going to use that as a reason not to go much below 1/2 a tank.

I agree with this reason and it is one of the main ones for me keeping the tank topped off. We are one North Korean or Iranian nuke (or some other unforeseen craziness) away from a major panic and possibly price rises or fuel unavailability. Sure this wouldn’t help you much long term but it would at least get you home and such.