I heard somewhere that no vehicle should be allowed to run on less than 1/4 tank of gas (or at least avoid getting too close to "Empty" mark). Something to do with the possibility of the fuel pump sucking up air, or something along those lines. Any truth to that?
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- Thread starter Russ
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Also, the fuel pump works harder with less fuel in the tank.
The fuel pump does get submerged in gas to keep it cool. Although sucking up air into your system shouldn't cause anything to be damanged.
You get air in the system when you change your fuel filters and pumps so I don't see a problem with that.
Your fuel pump is going to work just as hard with a full tank or a quarter tank
You get air in the system when you change your fuel filters and pumps so I don't see a problem with that.
Your fuel pump is going to work just as hard with a full tank or a quarter tank
Air, schmair... It's the water, if any is present in the tank. Water, being more dense than fuel, collects in the tank's bottom. Running too close to empty would ultimately allow the pickup tube to draw bottom sludge into the fuel line. However, with more states increasingly relying on ethanol as an oxygenator to limit emissions, and with ethanol's ability to hold water in solution, maybe the problem's automatically mitigated now where ethanol is in general use in highway motor fuel.
it is that gas is the pump coolant. Running one lower than 1/4 heats the pump up and lessens its life.
Couple that with not changing the filter often enough and its time to buy a new pump.
This is made worse by fuel injection when the pump runs the same gas thru the filter multiple times rather than once like in a carb system.
Filters for fi are also much better filters so they pick up more dirt.
When I mechaniced, many customers paid the price of not changing a fuel filter and running gas low in the tank.
If i had a fi car, i would change fuel filter every 10k miles to prevent this.
Dan
Couple that with not changing the filter often enough and its time to buy a new pump.
This is made worse by fuel injection when the pump runs the same gas thru the filter multiple times rather than once like in a carb system.
Filters for fi are also much better filters so they pick up more dirt.
When I mechaniced, many customers paid the price of not changing a fuel filter and running gas low in the tank.
If i had a fi car, i would change fuel filter every 10k miles to prevent this.
Dan
No, I believe that having more fuel in the tank increases the pressure on the intake side, thereby requiring less pressure boost from the pump itself.
I once had an in the tank fuel pump that was getting noisy, and it was definitely noisier at 1/8 tank than at a full tank.
I was once on a Boeing 767 flight of about 1000 miles, and the pilot was having fuel pump problems (he announced this because our departure was late) and he said that the solution was to put an extra load of fuel in the tanks, as the additional fuel made the fuel pumps work less hard as they did not have to raise the pressure as much (more "gravity feed" effect).
Maybe I am all wet, but it seems to make sense.
I once had an in the tank fuel pump that was getting noisy, and it was definitely noisier at 1/8 tank than at a full tank.
I was once on a Boeing 767 flight of about 1000 miles, and the pilot was having fuel pump problems (he announced this because our departure was late) and he said that the solution was to put an extra load of fuel in the tanks, as the additional fuel made the fuel pumps work less hard as they did not have to raise the pressure as much (more "gravity feed" effect).
Maybe I am all wet, but it seems to make sense.
fuel in an aircraft will "gravity feed" and run the engines without the use of the boost pumps. they probably made an error during fueling and had a hard time getting the pumps primed.
also pilots generally know nothing about the mechanicals of the aircraft, so an answer like" load more fuel to get the pumps to work better" satisfies them into taking the aricraft, when it could have been for "better" reasons.
i know many people, including myself, who run their tanks to empty, no fuel pump problems reported.
Boy, I seem to have a talent for long posts.
Hope I don't bore anyone to death.
Having recently replaced my fuel sending unit, I've learned a thing or two about how fuel pumps are installed, at least on my 2000 Monte Carlo. First, there are what looks like chunks of carbon inside the sock attached to the fuel pump to catch any sediment before it hits the pump. The pump assembly sits vertically in the tank and is pressed against the bottom of the tank by a pair of springs. This would prevent the pump from picking up any air unless the tank was VERY empty. Also, after 4 years and 80,000 miles, there were only a few very small bits of sediment on the bottom of the tank, and that might have come from removing the sender. Considering that I buy whatever gas I find cheapest, I doubt that dirty, contaminated gas is much of a problem any more. I'm sure there are instances of this happening (I've gotten bad gas in this car before), but after 80k, the inside of the tank looked clean as a whistle.
Anyway, getting back to cooling, the pump itself actually sits inside of a large, plastic shell. This prevents gasoline from coming into direct contact with the actual pump, meaning that any cooling would have to come from the gasoline that is actually being pumped. The ambient gasoline in the tank would have little to no effect on the pump's temperature.
I would also argue that, for a pump in good condition, especially in a vertical arrangement like mine where the fuel exits the top of the tank, the weight of gasoline will have almost no effect on the power required to pressurize the fuel. If your pump is noisy, it is on its way out. Keeping the tank full is only a bandaid.
Before I replaced my sender, I also thought that it's unwise to run lower than a quarter tank because of cooling, sediment and making the pump work harder. Now I realize there is nothing to any of that. The only reason not to run less than a quarter tank is so you don't run out of gas. In the winter, there might be an additional reason where condensation could be a problem (from dew forming inside the tank when the temperature drops at night, more gas=less opportunity for dew to form), but this is not an issue in warmer weather.
Finally, I realize that other cars may be different, but for mine, there should be no effect on pump longevity no matter how much gas is in the tank.
BTW, I replaced the sender because the gas gauge was erratic, not because of the fuel pump.
Having recently replaced my fuel sending unit, I've learned a thing or two about how fuel pumps are installed, at least on my 2000 Monte Carlo. First, there are what looks like chunks of carbon inside the sock attached to the fuel pump to catch any sediment before it hits the pump. The pump assembly sits vertically in the tank and is pressed against the bottom of the tank by a pair of springs. This would prevent the pump from picking up any air unless the tank was VERY empty. Also, after 4 years and 80,000 miles, there were only a few very small bits of sediment on the bottom of the tank, and that might have come from removing the sender. Considering that I buy whatever gas I find cheapest, I doubt that dirty, contaminated gas is much of a problem any more. I'm sure there are instances of this happening (I've gotten bad gas in this car before), but after 80k, the inside of the tank looked clean as a whistle.
Anyway, getting back to cooling, the pump itself actually sits inside of a large, plastic shell. This prevents gasoline from coming into direct contact with the actual pump, meaning that any cooling would have to come from the gasoline that is actually being pumped. The ambient gasoline in the tank would have little to no effect on the pump's temperature.
I would also argue that, for a pump in good condition, especially in a vertical arrangement like mine where the fuel exits the top of the tank, the weight of gasoline will have almost no effect on the power required to pressurize the fuel. If your pump is noisy, it is on its way out. Keeping the tank full is only a bandaid.
Before I replaced my sender, I also thought that it's unwise to run lower than a quarter tank because of cooling, sediment and making the pump work harder. Now I realize there is nothing to any of that. The only reason not to run less than a quarter tank is so you don't run out of gas. In the winter, there might be an additional reason where condensation could be a problem (from dew forming inside the tank when the temperature drops at night, more gas=less opportunity for dew to form), but this is not an issue in warmer weather.
Finally, I realize that other cars may be different, but for mine, there should be no effect on pump longevity no matter how much gas is in the tank.
BTW, I replaced the sender because the gas gauge was erratic, not because of the fuel pump.
Here's a pic of the old sender I removed, just to illustrate my points. The sock is sticking out of the bottom of the sender to the left side, right in front of the screwdriver.
I regularly run all my vehicles way low on gas. To date, only the '88 Chev has ever needed a fuel pump, and those go like clockwork (always between 60 and 70,000 miles - the truck is over 250,000 miles now).
The '88 Chevy Cavalier with 163,000 miles, the '97 F150 with 163,000 miles, the '88 Jeep Cherokee with 63,000 miles, and the '99 F150 with 107,000 miles all get drained nearly dry, and no fuel pumps among them.
My exception to the rule is in the winter, I generally stay above a 1/2 tank to minimize condensation problems that leads to fuel line freezeups, but that is less of a problem with 10% ethanol gasoline.
The '88 Chevy Cavalier with 163,000 miles, the '97 F150 with 163,000 miles, the '88 Jeep Cherokee with 63,000 miles, and the '99 F150 with 107,000 miles all get drained nearly dry, and no fuel pumps among them.
My exception to the rule is in the winter, I generally stay above a 1/2 tank to minimize condensation problems that leads to fuel line freezeups, but that is less of a problem with 10% ethanol gasoline.
uel pumps AWALYS pickup from the very bottom of the gank. if does not matter if you have a full tank or are runnin on empty, the pickup is awalys at the bottom where the sediment and water lie.
that is why we have replacable fuel filters.
the myth about keeping the tank full to prevent water or sediment from being picked up is completly untrue.
that is why we have replacable fuel filters.
the myth about keeping the tank full to prevent water or sediment from being picked up is completly untrue.
Last time I was in a 747 we were delayed on the ground because the "gas" gauge wasn't working, and the ground crews had to manually check the "gasoline" level in the tanks. Not fuel, not even gas, but gasoline.quote:
Originally posted by tom slick:
also pilots generally know nothing about the mechanicals of the aircraft
As for the fuel pumps, My last Cherokee, which my dad drove for 98,000 miles needed a fuel pump when I got it. He allways drove with an empty tank. My "new" Cherokee has almost 200,000 miles on the original pump, and I know the previous owner rarely let it go below half a tank.
I know on my car, any fuel sent up to the engine that's not used is sent back to the gas tank. Wonder how warm it can get an 1/8th of a tank of gas?
I'll bet this was due to the lower fuel level allowing a larger portion of the tank to vibrate than if it was full, causing the noise you hear to be louder. In other words, the noise was always there, but the gasoline dampened it when the tank was full.
Ummmmm. And you flew in the thing? I would have taken a bus at this point!!!!!!!!
The overheating thing was an issue with the first application of in-tank pumps. It no longer is, but the urban myth persists.
The 'sucking up sediment (and the 'sucking up water') is also an urban myth, and a very stupid one. The pickup tube is ALWAYS at the bottom of the tank. It doesn't move around with the level of gas in the tank.
The 'condensation overnight' one used to be true, but is no longer a concern with modern vapor recovery systems. Any modern car's tank is filled with pressurized fuel vapor, not outside air.
The 'sucking up sediment (and the 'sucking up water') is also an urban myth, and a very stupid one. The pickup tube is ALWAYS at the bottom of the tank. It doesn't move around with the level of gas in the tank.
The 'condensation overnight' one used to be true, but is no longer a concern with modern vapor recovery systems. Any modern car's tank is filled with pressurized fuel vapor, not outside air.
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