gas tank myth??

[Axel Grungy]

ok ive heard from a few people that its better to use the upper half of your tank rather than the bottom?? i usually just fill up half way and use the bottom half, is this bad?? ive had alot of clogged injector problems in the past btw. does using the bottom half cause more crap to be in the gas?

[whiterps13]

i know when my dad had a 1990 300zx, it would knock and run like **** when you let the gas get under 1/4 tank. it makes sense, but i wonder if there are some hard facts to support the idea..

[Bruno240]

i remeber my old 240sx would run like crap on the 1/4 left when it was cold. and once i filled up it would run fine.

[aesic]

I JUST refilled today. I don't know if I was imagining it or not, but I do think it was running worse before I filled it. It was just above the empty line. On my '91 S13, 123k miles.

-aesic

[Red coupe]

Ive always had my autoshop teachers tell me that the fuel pump is lubricated by the gas, so running on less then 1/4 of a tank can cause slightly more wear to it...

[Axel Grungy]

keep em coming, good info

[corn322]

I've always been fine on the bottom 1/4 of the tank

[Ligouri Rd]

I believe the issue is that over time gasoline absorbs a certain amount of water...specially in the winter if the car sits. Water is heavier than gasoline so it sinks to the bottom of the tank. Over a lot of time it could build up and below half a tank of gas you could be running partially water. Thats also why in winter you don't wanna run lower than half a tank, since the too much water in the gas can cause it to freeze...right in the bottom of the tank where the pick up is.I guess you could also have build up of crud at the bottom of your tank and running low could cause it to cake up on the pre-filter.

I tend to run my tank low before every time I fill up and have never had a problem. It probably wouldn't hurt to drain your tank every so often, i did that as a safety precaution when I swapped fuel pumps last winter.

[Thee 240sx Owner]

Ive always had my autoshop teachers tell me that the fuel pump is lubricated by the gas, so running on less then 1/4 of a tank can cause slightly more wear to it...

very true

[InsanityInc]

In some cars (the 240 isn't one of them) fuel starvation can occur at fairly high fuel levels (1/4 tank) and make the car run oddly. Running it down low isn't an issue besides starvation, and you won't pick up any crud because the pump has a filter on it.

[vvaffle]

I know that in the winter the less gas you have in your tank, the more water vapor can get in and then it condenses inside your gas tank. So technicaly it would be the best to keep your tank full in the winter.

[Veriest1]

Ive always had my autoshop teachers tell me that the fuel pump is lubricated by the gas, so running on less then 1/4 of a tank can cause slightly more wear to it...

I've heard this from numerous sources as well. All above the age of 40.

I believe the issue is that over time gasoline absorbs a certain amount of water...specially in the winter if the car sits. Water is heavier than gasoline so it sinks to the bottom of the tank. Over a lot of time it could build up and below half a tank of gas you could be running partially water. Thats also why in winter you don't wanna run lower than half a tank, since the too much water in the gas can cause it to freeze...right in the bottom of the tank where the pick up is.I guess you could also have build up of crud at the bottom of your tank and running low could cause it to cake up on the pre-filter.

I've been told (haven't tried it) that a bottle of rubbing alchohol or two would absorb the water and run through the fuel sys. Anyone know anything about this?

[GEO]

get bigger fuel socks and you won;t have to worry about fuel starvation

[AZhitman]

So far, to my knowledge, all *mostly* correct info.

Below 1/4 tank, the fuel pump is not COOLED by the surrounding fuel, which can cause problems (it's especially bad on the Q45).

Modern fuel pumps aren't "lubricated" by the surrounding fuel, as they're sealed.

There are additives you can add to absorb water.

There is a certain amount of particulates and "sludge" that accumulates at the bottom of the tank after several years. No sense sucking that mess into your filter.

[GEO]

greg, tell them to get larger fuel socks.

[comablack783]

may sound like a silly question, but how would you go about draing your tank?

[fatboy]

everyone missed the most important thing. the main thing that kills a fuel pump is heat. the reason fuel pumps on newer cars are put in teh tank is to cool the pump. premature failure of fuel pumps are a lot of times caused by cars that constantly run lkow on gas. also, on a lot of new cars, the sending unit for the gas gauge is on teh pump, so a lot of times, the sending unit and be damaged

[AZhitman]

^

Precisely.

[fatboy]

^

Precisely.

im sorry, you already mentioned that.hahaha. in anycase, we're thugs! actually, i know that over my years working at car dealerships. i work at a lincoln/mercury dealership and i cant count how many super rich people that can afford to buy a 50+g vehicle comes in empty!

[GhostDriver]

Looks like its time for a fuel up....damnit.lol

[1WheelWonder]

Wow, this is very informative, never thought about this subject.

[Florida240sx]

I let my tank run low abotu once a month.And abotu 3 times in a row before I do a filter swap.

[skydragoness]

I always fill right when it hits the 1/4 mark, up to halfway.

[GrilledCheese33]

yea, but see when i go 2 weeks without filling, i am about 400 miles on the trip and fill up with only 13 gallons and teh s14 tank holds around 17, so i don't think i have a problem on this issue. But i always fill on friday b/c premium is 10 cents off per gallon at the local station 7 blocks away, and I get it for 2.39 a gallon! BUt i really never thought of this at all. You learn something new everyday!

[onosqv]

Less gas = less weight = better fuel economy, HAHAHA.

Where do you buy bigger fuel socks? I know the guys @ autozone/kragen/etc aren't particular helpful, i.e. they always ask "just give me the specific model/year of your car & the computer will tell me what you need."

Seafoam in the fuel tank?

[Ligouri Rd]

Quote »I've been told (haven't tried it) that a bottle of rubbing alchohol or two would absorb the water and run through the fuel sys. Anyone know anything about this?[/quote]I wouldn't try rubbing alcohol, but fuel additives like heet are supposed to take absorb any water that is in the fuel.

[Axel Grungy]

well i filled my tank up and for some odd reason it seems like it runs better, or maybe its all in my head....stupid brain

[drifter_for_life06]

been running the same since the 1/2 tank mark

maybe ill notice soemtihng at full takn

[tonynalli]

honestly i have not ever had this problem.i am constantly running low on gas almost everytime i have the light on before fill up....and out of all the 5 240's that iv had ive done the same, i wonder why that is? not to sound like an *** or anything.