Why Is Running A Tank On Low Bad?

[Imzjustplayin]

What would be the reason for running a fuel tank on low be a bad thing? I've heard that you have to worry about all of the 'gunk' that collects at the bottom of the tank and thats why it would be a problem but isn't the fuel drained from the bottom of the tank anyways? So if the fuel is taken from the bottom of the tank, why would it matter if you're taking the last bit of fuel?

[RFeldes]

The fuel pump heats up from low levels thus shortening the life of the pump.

[91LS400vgb]

Yepper, the fuel acts as a coolant for the fuel pump and if you run low on gas, the pump can overheat.

[ED.]

yeah like those gyus said running it on E shortens the life of the pump. although my mom use to live on the yellow light on her 4 runner and never really had too many problems but i still prefer to not let it get lower than a 1/4 tank for the fuel pumps sake and my wallets! : )

[05silverls430]

If there is sediment in the tank, doesn't running it low make it more likely that it will get into the fuel filter and clog it?

[bossman]

For those of us further north, and out of concern for winter driving conditions, keeping the gas tank above half a tank is very important. As the temperature changes during the day, condensation can form inside the gas tank. This condensation (water) can get into the fuel line and freeze. This will then cause big problems for your fuel pump. During the winter months, I try to keep my gas tank as full as possible at all times.

[Gryphon]

Four fuel pumps so far on my 1998 Yukon that my wife routinely runs on fumes before refueling. Could very well be overheated fuel pumps.

Tom

[SKperformance]

I always run mine down to the bottom before filling up to remove any deposits and anything else to get burned or inserted into my fuel filter.

I have not had any issues with my pumps. But i also don;t wait to stall from no gas all the time which will heat the pump up and shorten its life.

[my ls430]

the fuel pump can heat up and catch on fire.....not good

[05IS300]

I say it's BS about running your tank low.If you notice the only person that has changed a pump is on a Yukon.GM pumps are junk,we've replaced 3 on our 93 4x4 GMC that has 50k.I run all my cars till the light is on with no problems.I have a 90 2dr 4runner with 254k,a 98 Sienna with 140k,a 90 LS with 288k and my Dad has a 92 4x2 Toyota with 256k that all get run to the E and all have original fuel pumps.As far as picking up the dirt at the bottom, the pickup is located at the bottom of the tank,so it is always getting the fuel from the bottom of the tank.Oh yea,my IS300 has 10k with no problems yet.

[Thermactor]

The fuel pump is cooled by the gasoline running through it, not through the gasoline it's immersed in.

[Gryphon]

The fuel pump is cooled by the gasoline running through it, not through the gasoline it's immersed in.

If so, then why are fuel pumps inside fuel tanks where they are much more expensive to access?

[SRK]

The fuel pump is cooled by the gasoline running through it, not through the gasoline it's immersed in.

Simple physics here. The fuel acts as a coolant - more is sent to the engine than is used, and the excess is returned to the tank. This cools the fuel rail in the engine compartment, and prevents vapour locking. As a result WARM fuel is returned to the tank. If the total volume of fuel in the tank is small, there is less time for the fuel to dissipate heat before it is sent back to the engine. The fuel temperature in the tank then rises. As it does so it has less and less ability to cool the fuel pump. Keep in mind that in-tank pumps operate at up to 5000 RPM and draw 4-8 amps, which is why they need cooling. So it's a good idea to keep at least a quarter tank of fuel.

Many fuel pumps are located in a small "well" within the main tank to keep the outside of the pump in fuel until the tank runs dry. Obviously it's important enough to justify this modification within the tank.

Have a look at the saddle tanks on a large semi-tractor on a rainy day. If the truck has been running for some time the tanks will be steaming or even dry, while the rest of the truck is wet, due entirely to the heat of the fuel returned from the engine as part of the injection cooling circuit.

[Darrell J]

I have read some great answers... And they are right about the fuel pump needing cooling.. and also water pumps, fuel pumps need liquids to run through them or they will burn out..

Also.. I used to run my cars especially the lexus "UNDER THE RED LINE"

and finally i started keeping it over 1/2 tank and I can honestly notice a differece...

More gas.. better ride

[SuperCoupe400]

I LIVE below "the slash". Always have on every car I've owned. And all the way up to their demise('86 Renault Alliance; '91 Integra w/273k mi), never once did I have issue with fuel pumps needing replacement. Even living in Michigan I take no thought about letting my car sit outside my office all day long in 26-degree weather on E. I've never had the dreaded Urban Legend of "Your gas will freeze!" happen. I can't tell you how many people up here actually believe that myth.

Besides, and i'm no scientist, but isn't the fuel tank and injection line a "closed" system - assuming that the gas cap has been properly tightened? If so, then upon the presence of sub-freezing teperatures when condensation would normally occur, where is this condesation coming from? Not from outside the closed system. It's coming from the gas that's in the tank already - right? :whistles: So what harm can come from this condensation then being mixed back in with the very gas from which it came? :( Not being sarcastic. Just trying to piece together why it is this thing that's suppossed to be so dangerous to the fuel pump has never once effected me in all my years driving like that.

I started driving that way when I got my first car in college (scratching by from payday to payday) and it just formed a habbit that was never really proven to be a bad one. (Never once ran out of gas - knock-knock)

[Paul Sherman]

OK, just to stir the pot some more...

Frozen fuel line - had it happen once. In a Ford Caprii

I drove while in the Shetland Islands. At the time, it

was called 'vapour lock'; the water froze while in the

fuel line, which was exposed to the freezing, moving

air (wind chill).

Condensation - an argument for keeping the tank

filled up. Condensation comes from the air in the tank,

not the fuel. The less fuel, the more air, more condensation.

Fuel/water ratio: Water in the tank - it's inevitable. As the

vehicle moves, the water and fuel are mixed and get

pushed through the system. However, that mixing isn't

perfect (though improved over carbed engines because

of the return flow). Hence some settling of water in the tank

is also inevitable. As the fuel level drops, the proportion of

water to fuel will increase, risking the the bad stuff mentioned.

Side note - not all GM pumps are bad. My '69 pickup with

335K on it has ~120k/15 years on the current fuel pump.

This rig's a candidate for all the bad fuel/water fears mentioned -

it's never happened.

Paul

[DanW]

I say it's BS about running your tank low.If you notice the only person that has changed a pump is on a Yukon.GM pumps are junk,we've replaced 3 on our 93 4x4 GMC that has 50k.I run all my cars till the light is on with no problems.I have a 90 2dr 4runner with 254k,a 98 Sienna with 140k,a 90 LS with 288k and my Dad has a 92 4x2 Toyota with 256k that all get run to the E and all have original fuel pumps.As far as picking up the dirt at the bottom, the pickup is located at the bottom of the tank,so it is always getting the fuel from the bottom of the tank.Oh yea,my IS300 has 10k with no problems yet.

I've had a couple GMs ('95 and '01 and never again) and I'd have to agree. The most likely explanation for cheap low quality parts from Mexico failing is that they're cheap low quality parts from Mexico.

[blake918]

I've heard that you have to worry about all of the 'gunk' that collects at the bottom of the tank and thats why it would be a problem but isn't the fuel drained from the bottom of the tank anyways? So if the fuel is taken from the bottom of the tank, why would it matter if you're taking the last bit of fuel?

I've heard that one about the gunk at the bottom of the tank too! It's priceless! I run my car far in to the E because I hate having to stop for fuel. I've never had any problems, and my car has 287k miles. On a pure interstate run, I'll go at least 500 miles on a tank, and there are still a couple gallons left. My low fuel light comes on when I have 5 gallons left--that sure is a lot of remaining fuel to have a warning light come on. To me, this is like worring about starting the car with the a/c compressor on.....it might make a difference after 500,000 miles. LOL

Ahhh, good ole GM truck fuel pumps! We replaced the one in our '99 Suburban once. You can tell whether or not they work before you even leave the house...if you turn the key and your neighbors can hear the pump whining, then you are good to go! LOL

[SuperCoupe400]

You know, it sounds to me as if these worries about fuel lines freezing, sludge (gunk) collecting at the bottom of the tank, vapor lock, etc., etc., etc. are things that only people on the "Dark Side of the Force" - GM, CHEVY, FORD - (you know, old hooptie domestics) need be concerned about.

We seem to have several people here, myself included, who have defied and continue to defy what those in hooptie-ville would consider the kiss of death to a cars fuel system, fuel lines or fuel pumps. :o

In other words - these things just don't seem to apply to Lexus, because Lexus automobiles are engineered the RIGHT way. ;)