POLL: when do you fill up your gas tank?

[Jeff7181]

After sitting all day in the sun, wouldn't the gas be the same temp as the air? Why would it make a difference for cooling? After all, the fuel pump has gas running through it at all times - wouldn't that act as a cooling agent if you say that gas cools the pump?

Yes, which is why it doesn't fail immediately, or minutes later. I'm speaking from experience, and from the teachings of people with over 30 years in the business. Running the tank dry WILL cause premature failure of the fuel pump. There's no question about it. And the funny thing is, the fuel pumps last just beyond your new car warranty. Some owners manuals even say to keep the tank at least 1/2 full.

On a different subject, ever think about a fuel pump, which is an electric motor, being located in your gas tank? Electric motors naturally create a spark or two during operation... turn on an electric drill in a dark room and look in through the vent holes. That's why it's important to have your gas cap tightened down properly. If it's not, and air gets in... now you have a mixture of oxygen and gasoline vapors and sparks... not a very calming thought is it?

*EDIT* I've replaced a seized fuel pump twice in one car before. The motor actually got hot enough to make the metal expand to the point that it seized. This was in a car where a lady would visit a small gas station, hand the clerk a $5 bill, go put $5 in her tank... drive 35 miles to work... drive 35 miles back home after work, and do it all over again the next day. She never filled her tank completely.

 

[DrPizza]

Originally posted by: jumpr

Originally posted by: Jeff7181

Originally posted by: jumpr

Originally posted by: Jeff7181
It's not good to run fuel injected cars down to empty. The fuel pump is in the gas tank... it uses the gas to cool it down... if you run it down past 1/2, the fuel pump is no longer submerged and can't be cooled. That's why if you constantly drive on empty, and don't even fill the tank when you get gas, I bet you already have, or will be replacing the fuel pump.

Uh, what kind of idiot engineer would locate the fuel pump in a place where damage would occur when the fuel level is less than half? I don't know ANYONE who fills up at 1/2 tank - I personally wait 'till it's at 1/4.

I call bullsh!t on this answer - if you caused damage to your fuel pump below 50% a tank, then it'd be a pretty big deal.

I'm not saying if you run below 1/2 you'll damage it instantly. If you do it constantly, it will fail prematurely... ask any technician/mechanic/car enthusiast.

After sitting all day in the sun, wouldn't the gas be the same temp as the air? Why would it make a difference for cooling? After all, the fuel pump has gas running through it at all times - wouldn't that act as a cooling agent if you say that gas cools the pump?

Tell ya what... we heat two identically sized pieces of steel until they're red hot. You cool yours in air for 30 seconds, and I cool mine in water at the same temperature as the air for 30 seconds. Then, we grab the steel in our hands. Jumpr called Bullsh!t for the wrong reason: "what kind of idiot engineer would" use a flammable substance as a coolant?
It has to do with the specific heat of the material acting as a coolant (how much heat it can absorb) and a little bit on the thermal conductivity of the material.

Nonetheless, I still call shenanigans on the original answer... The pump simply cannot get hot enough that using the gasoline as a coolant is that important. I highly doubt therefore that the pump can attain temperatures where it would contribute to premature failure of the pump. If that were the case, then as the depth of the gasoline fell, the temperature of the pump would rise... and, if one ran out of gas, but left the ignition on, the pump would continue to run and further heat up. (while one walks to the gas station, gets a gas can with 1 gallon of gas in it, returns to car, starts adding the gasoline to the tank, and KABLAM! as the gas hits the overheated pump).

 

[LAUST]

Originally posted by: Lifer
i drive until I'm almost completely out. i see the 'low fuel' light almost everytime.
saves me extra trips to the gas station 😀

Also lowers teh life of your fuel pump as it has to work harder and is not cooled down by fuel in the tank

 

[ElFenix]

when the tank is almost empty

 

[compudog]

At $1.65 a gallon, whenever I can!!! I love spending money on gas. I drive with the AC on and the windows down, I drive with the parking brake on, full throttle in low gear! Sometimes I pump some right into the waste can aside the pumps because I LOVe paying for gas!


Seriously, when it's about 1/4 full.

 

[NutBucket]

Originally posted by: rh71
I caught wind of the fact that on Honda's (maybe especially Accords), it's bad for the car when the light actually comes on. As a result of this (perhaps freak occurrence)... our 90 accord was stuttering in the subsequent miles after the re-fill up. I've kept it no lower than 1/4 full since then and only recently has it been acting normal again.

My Rodeo has been fine through 8 years of gas lights... but I try to fill up just before it hits the E-line where it'll alert me.

Well, lets see. When the gas light comes on in my 91, there's still a good 4 gallons left. And 200 miles is pretty crappy mileage. I average about 29mpg in mixe driving and usually don't need to fill up until the trip meter is past 400.