Gas: Full up or half a tank???

Setec Astronomy said:
Well there's no two ways about it, keeping the tank fuller will lessen the amount of condensation (water) in the tank, whether that makes an operational difference or not is another story. An occassional shot of Heat or Dri-Gas can't hurt.
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I don't see how this can happen - the water in gasoline is already "condensed", i.e. it's already in the gasoline, and the only way for it to condense in the tank walls is for it to evaporate from the gasoline. This means you have to heat up the gasoline to get the water to evaporate, then the evaporated water can condense to go back in the gasoline... this clearly doesn't happen.



Once there is water in the gasoline, and you pump it in your tank, it will stay there until it gets sucked into the engine, or it gets mixed with the ethanol.



Water in gasoline is rarely a problem in city environments - maybe in remote areas where storage or transport isn't perfectly sealed...
 
hockeyplaya13 said:
If you go below 1/4 of a tank it will shorten the life of the fuel pump and they aren't exactly cheap. But I'm sure you could do the math to figure out how much gas you would save from not carrying that extra weight and it would probably be more than the fuel pump.
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How will low fuel in the tank lessen the life of a fuel pump?
 
Bebopp said:
Gasoline floats in water, so the water will be at the bottom of the tank, not the other way around. As soon as you get water in the tank, it's the first thing that gets sucked in the engine so having either half or full tank doesn't matter. You need to avoid getting water in the tank in the first place.
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Sorry, I was having a brain fart (sometimes I get too much stuff in my head and it pushes some other stuff out...or it could be I was at work and had half my brain occupied). The fuel pickup, whether it is in a vehicle or a stationary tank (gas station) is above the bottom of the tank to preclude water ingestion unless the water reaches a certain level. That's why gas stations use something like this: Water and Gasoline Finding Paste when they are sticking the tank to make sure the water level doesn't get to the height of the pickup (at least that's what they did last time I worked in a gas station...in the last century). Stirring up the tank by filling it or jostling it complicates things.



Fact of the matter is, unless you continuously top off your tank, you will get air in your tank, which will have moisture in it, which will condense under the proper circumstances (this of course includes the stationary tanks as well). Fuel system engineers know this, and design to tolerate a certain amount of water in the system. Periodically using an absorber will reduce the accumulation of water in the system, as will periodic draining (usually reserved for extreme problems). Honestly, I can't remember the last time I heard of someone having a water-in-the-gas problem.
 
Bebopp said:
I don't see how this can happen - the water in gasoline is already "condensed", i.e. it's already in the gasoline, and the only way for it to condense in the tank walls is for it to evaporate from the gasoline. This means you have to heat up the gasoline to get the water to evaporate, then the evaporated water can condense to go back in the gasoline... this clearly doesn't happen.



Once there is water in the gasoline, and you pump it in your tank, it will stay there until it gets sucked into the engine, or it gets mixed with the ethanol.



Water in gasoline is rarely a problem in city environments - maybe in remote areas where storage or transport isn't perfectly sealed...
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When you draw fluid out of closed tank, you will pull a vacuum in the tank which will prevent fuel draw and cause pump cavitation. The pressure is equalized through vents which let air into the tank to replace the volume of the fluid withdrawn. The air is of course, ambient air, which contains moisture. If the tank is refilled while the temperature of the air is above dewpoint, the "moist" air will be expelled during the filling process (which of course with today's vapor recovery systems, means that moist air will go back into the underground storage tank). If the tank cools below dew point (say, you fill up in the morning, drive off some portion of the tank which is replaced by ambient air, then park the car for the night), the moisture in the air will condense, just as it does on the outside of your car (dew).
 
For the garage queens we need to keep the tanks full. Moisture in the air condenses as it cools and so the more air in the gas tank the more water will condense.



Our gas is so junky you need to use stabilizer. I've had gas in a lawn mower (admittedly a less high tech machine) refuse to ignite after three months of outside storage.



Fuel pumps need cooling and that's what the gas in the tank provides.



OCCASIONALLY you need to run it down to nearly empty to help burn off residue, gunk etc. Otherwise it will build up.
 
BigJimZ28 said:
the gas keeps the fuel pump cool the more gas the longer the pump will last
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That's presuming that the fuel pump is damaged by temperatures below the boiling point of gasoline. If the pump is immersed, it can't get hotter (other than local hot spots) than the boiling point of the coolant (which will be somewhat increased by positive tank pressure, if that exists). I presume you think the bulk temperature of the fuel in the tank will be increased by traveling thru the fuel rail in the hot manifold area and back to the tank (plus frictional heating from the pumping), but the ambient is quite a bit lower than fuel rail temp...my gut feel is the fuel in the tank isn't going to get heated much in the final analysis...heck, the tanks are plastic today (which of course reduces the radiation and skin convection due to the lower thermal conductivity of plastic vs. metal, which means the fuel could be hotter today than way back when).
 
P1et said:
I have a '97 Dodge that has had the same fuel sitting in it for almost two years now. I haven't started it yet, but am hoping it will be just fine.



The above post, however, scares me a bit!
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I let the XJS sit with the same untreated gas for several years once, no problem. But I guess that doesn't mean that your experience will work out as well :nixweiss



Given how long your Dodge has sat, I'd disconnect the fuel pump and crank it for a while (with no fuel delivery) to pre-lube everything before you try actually starting it up.
 
Accumulator said:
The gas in the Jag sits there for a *lot* longer than a month...actually a month is nothing for my vehicles, many of them sit for that long at a stretch. I've *never*, not once, had a problem with gas in an auto going bad and I've never used any stabilizer additives.
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Yeah, the doctor that I detail the vintage 450 SEL for lets his car sit and never starts it or add stabilizer. The gas has got to be at least a couple years old (refreshing a few gallons like once a year). The car always starts on the first crank after a little priming. We fired it up last weekend to pull out to snap some photos for him so he can send them in with his application for antique plates.



He does use stabilizer for his vehicles at his vacation home that just sit there unused for years like an old Honda Prelude, Buick station wagon and a 1948 Lincoln Cosmopolitan with suicide doors.



As far as my cars, I never allow to drop below a 1/3 of a tank. I just sold my 12 year old Honda Civic that was getting 30 mpg on the highway with no additives or cleaners. The only thing I would do is change the fuel filter a bit earlier.
 
I drive an Alfa so anything less than an indicated 1/4 of a tank probably means an empty tank...or its half full or quite possibly 90% full
 
I usually fill it when it gets to half a tank, for the above mentioned reasons. I always have gas which is good in the winter, and if I am short on money I can drive a little while. You can't do that when it's empty.
 
Lowejackson said:
I drive an Alfa so anything less than an indicated 1/4 of a tank probably means an empty tank...or its half full or quite possibly 90% full
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What is that, a "Lucasazione" fuel level sender? :LOLOL
 
Setec Astronomy said:
I regularly go below 1/4 tank and I had my last car for 16 years/125K miles with no fuel pump replacement :nixweiss
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Lucky. We had the suburban for 5 years and then had to replace it. The guy told us not to go below 1/4 of a tank, but I don't remember if we went below that regularly or anything so I don't know if that was the cause or not. I'm just saying what he said.
 
Work in an automotive development lab for 20 years.



Keep it full.



When filling your tank at the station, pump no faster than the mid setting.
 
Pump readout feedback is calculated using the feedback port (kicks it off when full). The higher the speed the more that air in venturi form (zipping past the feedback port) increases readout error. In effect you are paying for air. Further, though to lesser effect, the higher the fill speed the more air is incorporated into the fuel (temporarily) thus again you are paying for air. An exagerated example of this would be whipped cream.
 
Don't forget, todays gas now has 10% Ethanol which is VERY hydroscopic. Not a good thing. Even with this season blends, it's still Ethanol.



If you're going to store a car for winter, when level is about 1/2 tank, add Sta bil, then add gas to mix. Drive it long enough so it's in the fuel system. Make sure tank is full. Then you can proceed to the rest of winter prep.



Also, if after all your hard work cleaning/detailing the car including the underside, if you have a concrete floor, put a heavy plastic sheet down before rolling the car into the garage. Why? Moisture can wick-up and start rusting items. I also add mositure absorbing bags in the interior, trunk and engine areas.



The rest, battery maintainer, covers etc is up to you.



This is part of my prep before storage.



Deanski
 
Deanski said:
Don't forget, todays gas now has 10% Ethanol which is VERY hydroscopic. Not a good thing. Even with this season blends, it's still Ethanol.



Ethanol is also aproximately half the energy. Thus you are paying 2x for the ethanol part. It is a real rip off.



If you're going to store a car for winter, when level is about 1/2 tank, add Sta bil, then add gas to mix. Drive it long enough so it's in the fuel system. Make sure tank is full. Then you can proceed to the rest of winter prep.



Perfect!



Also, if after all your hard work cleaning/detailing the car including the underside, if you have a concrete floor, put a heavy plastic sheet down before rolling the car into the garage. Why? Moisture can wick-up and start rusting items. I also add mositure absorbing bags in the interior, trunk and engine areas.



On top of the plastic sheet, use cardboard, it wicks the remaining ambient moisture away from your car. Put a few open empty cardboard boxes in the seats, and trunk. In the engine compartment use flat cardboard. FYI keep cardboard onder lawnmowers, snowblowers, garden tools, and so on for the same reason.



The rest, battery maintainer, covers etc is up to you.



This is part of my prep before storage.



Deanski
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Is it good practice to remove the battery?



What should be done to preserve tires?
 
KnuckleBuckett said:
Pump readout feedback is calculated using the feedback port (kicks it off when full). The higher the speed the more that air in venturi form (zipping past the feedback port) increases readout error. In effect you are paying for air. Further, though to lesser effect, the higher the fill speed the more air is incorporated into the fuel (temporarily) thus again you are paying for air. An exagerated example of this would be whipped cream.
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I think my brain just melted. :scared:



So is the main point that we should not lock the filler nozzle on that very last notch? Would I end up putting more gasoline into the tank if I filled it slower?
 
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