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Author Topic: Cold night = cracked gas tank?
Talenyn
The Red and the Green Stamps


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My car knowledge is pretty much restricted to turn key, car goes. So when my Da suggested that I should keep the tank a quarter full to keep the gas from freezing, I bought it. Until recently… when I was driving my SO home and mentioned that we needed to stop to buy gas so it wouldn't freeze, and he laughed at me. Now does anyone actually know if prolonged sub-freezing temps. will really freeze the gas in my tank, or why a measly quarter of a tank will prevent this?

Talenyn


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dilbert
The Red and the Green Stamps


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I could see a point in the fact that water does tend to collect in a gas tank. However, since gas has such a low freezing point, I could see that keeping gas in the tank will prevent the possiblity of not being able to get the gas out of the tank.. but in general it's a good idea to keep at least 1/4 tank full anyway to keep from sucking any dirt/water out of the tank into the engine.
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BoKu
Happy Xmas (Warranty Is Over)


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quote:
Originally posted by Talenyn:
...my Da suggested that I should keep the tank a quarter full to keep the gas from freezing

Oh, grack, Talenyn, you'se been taken. It's like you've been sent out to get a bucket of propwash or a left-handed monkey wrench.

I don't know what the freezing point of gasoline is, but I know that it stays liquid at some pretty incredibly low temperatures. So it is basically a complete non-concern.

However, there is one good reason to keep the fuel tank as full as practical: condensation. Atmospheric air has a lot of water in it, and as you use the fuel in the tank, it is replaced through a vent with air. Over the temperature cycle of the day, the water in the air condenses on the inner surface of the tank, causing droplets that will cause rust or corrosion inside the tank. The more full you keep the tank, the less area there is to be affected by the condensation, and the less rust or corrosion you'll get.

The corrosion of the tank itself is pretty much a secondary concern. The real problem there is that the corrosion creates tiny flakes of metal oxides that can clog parts of the fuel delivery and injection system. That'll cause the car to run poorly or perhaps not at all.

However, even the tank-corrosion concern is going away - many newer cars have plastic gas tanks that are impervious to corrosion. Even still, the droplets of water in the gasoline are generally not good. If enough water collects in the system, it can eventually cause hard-to-diagnose bouts of poor running. It can also, given cold enough temperatures, freeze and clog the system, also causing some mysterious symptoms.

So I guess there are a couple of grains of truth to what they're telling you, but they're pretty small.

Bob "can't open canned food" K.


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IrateDwarf
Asparagus Spears


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I have a funny story my dad told me happened to him when he was about 17.

It was winter time, and my dad and some of his friends were getting ready to go snowmobiling. My dad's friend brought over his snowmobile and wondered if there was any gas left over from last winter. Not having flashlight, and since my dad's friend smoke, he pulled out a match and foolishly lit it to check for gas. BOOM! The gas tank exploded and my dad's friends hair caught on fire.

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"Air?"
"There's no air in space!"
"There's an Air in Space Museum!" - The Simpsons


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Chris M
The Red and the Green Stamps


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quote:
Originally posted by BoKu:
However, there is one good reason to keep the fuel tank as full as practical: condensation. Atmospheric air has a lot of water in it, and as you use the fuel in the tank, it is replaced through a vent with air.

This is correct, so far.

The gas tank is galvanized, so the little bit of condensation that gets into it won't cause much corrosion in the tank.

But, the droplets of condensation that do get into the gas line when you shut down the engine may freeze in very cold weather. Like the weather we routinely get in certain parts of Canada.

This has happened to my car on more than one occasion.

I wouldn't worry about this unless you're expecting temperatures of -25C or lower. Otherwise, the odds are just too low.

If you routinely expect this kind of weather, keep your tank more than half full, use gas-line anti-freeze every other tankfull equivalent, but stop before the weather warms up significantly.

Gas-line antifreeze will tend to raise the burning temperature around the igniters, and can cause a bit of extra wear.

I don't bother with gas line antifreeze in Halifax, as the temperature tends to stay mild enough not to matter so much.

But I've endured (humid) -30C weather for weeks on end in Fredericton the few years I've lived there. It made all the difference.


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BoKu
Happy Xmas (Warranty Is Over)


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quote:
Originally posted by IrateDwarf:
I have a funny story my dad told me happened to him when he was about 17....

Oh, that's priceless - but only if nobody was seriously hurt.

[warning: goes for a long semi-technical trip through the OT weeds ahead]

That story demonstrates one pequliar quality of fuel tanks; namely that they're generally a lot more dangerous when they're nearly empty than when they're full.

The key is a qualitiy called stochiometricity. A stochiometric mixture is one in which a fuel and an oxidizer have been combined in a mixture that, after combustion, will leave no leftover fuel or oxidizer. A stochiometric mixture is the most effective mixture for combustion. For gasoline, stochiometricity is reached at a air/fuel ratio of about 14.7 to 1 by mass.

A full fuel tank has little or no room left for air, so a fire inside the tank will quickly use up all the available oxygen and then just die out.

A good example of this is found inside the electric constant-displacement fuel pumps in most fuel-injected cars. Basically, the entire electric motor is submersed in gasoline, which cools and lubricates it. That little DC motor has a commutator and brushes like any DC motor; and as an inevitable byproduct produces a nearly constant spark near the brush/commutator interface. So you've got constant fuel and constant spark, why no trail of fire behind nearly every car on the highway? The answer is, no air. In addition to fuel and ignition, you gotta have air.

A nearly empty tank, however, gets much closer to the ideal 14.7 to 1 ratio that liberates the most energy. With all that air in there, a fire will quickly burn the atomized fuel in the air above the liquid fuel. It will also heat and vaporize the liquid fuel, and also agitate the mixture. Big bang.

That's what most people think happened to TWA 800. The two air conditioner systems in the 747 are run by little turbine engines - basically little jet engines. The air conditioners are basically heat movers; they cool the cabin of the airliner by heating up the outside air. Also, the turbines that run the system generate no little heat themselves. Since the airconditioner systems are located near the center main fuel tank where the wing passes through the body of the airliner, a lot of heat gets radiated and conducted into the fuel tank. On the flight in question, the center tank was basically empty, having only about 50 gallons sloshing around in the bottom.

So the center main tank contained a very nearly stochiometric mixture of kerosene and air, a mixture that was heated up by the airconditioning system. The takeoff and climbout further agitated the mixture for better atomization, and the atomized kerosene was relatively close to its flash temperature. Given those combustion-friendly conditions, it wouldn't have taken much of an ignition source to set it alight. And when it did go off, the near-stochiometricity of the mixture caused it to be as effective a combustion as possible.

What lit off the center tank? Nobody is sure. All the usual suspects were incinerated or obliterated. And there were lots of suspects. There were electric fuel level sensors. There were conduits through the tank for wiring bundles. There were wiring bundles around the tank that might have ignited a leaking mixture. There might even been electric fuel pumps inside the tank, but I don't know that much about 747s.

Of course, the general exception to the more-dangerous-when-empty rule is when you crush the tank and squirt the fuel into the surrounding air. Given that this generally encompasses a much greater volume of air than the inside of the tank, you get a much more nearly stochiometric mixture, with potential for a frightfully big fireball. That's what makes the Pinto and early Mustangs such a fright in a rear-ender.

With race cars and military airplanes, what they sometimes do is fill the fuel tanks with a spongelike material that will release fuel at a rate sufficient to meet the demands of the engine, but not much more. When you crush those tanks, you get dribbles and streams,and maybe gushes, but not huge atomized clouds of volatile mixtures.

Since fuel tanks are usually safest when either full or chemically purged of all fuel, some aviation museums keep their display aircraft fully fueled. They ask visitors not to smoke around them...

Bob "Pinto beaned" K.


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LizzyJingleBells
Ding Dong! Merrily on High Definition TV


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If you are truely concerned with gas tank freeze, there are products on the market to prevent that. But you usually only find them in the really cold climates. I don't think keeping 1/4 of a tank will do that. But, as dilbert said, it's good not to let it get too low, just so you don't run out in the middle of nowhere!

Lizzy "I've got gas!" M

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~Catherine Aird

{400 posts! Hey, how come I'm still a grape nute?}

[This message has been edited by lizzym5150 (edited 03-19-2001).]


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Chava
The Red and the Green Stamps


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When I lived (briefly) in the Frozen Northland of Iowa, I used to put gasline antifreeze in the tank. If I didn't, and let the tank get low, I would get symptoms similar to dirty fuel filter which were presumably from small crystals of ice in the gas. The antifreeze is alcohol, which dissolves water (seems weird to think about one liquid dissolving another, but that's what happens). Nowadays gasoline many places is supposed to have some percentage of alcohol in it for smog control during the winter and that might be adequate for antifreeze as well. No experience, since it doesn't get that cold in Tucson.

Chava


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Chris M
The Red and the Green Stamps


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quote:
Originally posted by Chava:
No experience, since it doesn't get that cold in Tucson.

I found it hilarious that, when I went to Tucson last year on a 2 day business trip in the deepest, coldest part of winter, that the temperature in Tucson was exactly the same as warm (but not hot) summer weather here in Halifax.


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Cool Hand Luke
The Red and the Green Stamps


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quote:
When I lived (briefly) in the Frozen Northland of Iowa, I used to put gasline antifreeze in the tank. If I didn't, and let the tank get low, I would get symptoms similar to dirty fuel filter which were presumably from small crystals of ice in the gas.
The antifreeze is alcohol, which dissolves water (seems weird to think about one liquid dissolving another, but that's what happens). Nowadays gasoline many places is supposed to have some percentage of alcohol in it for smog control during the winter and that might be adequate for antifreeze as well. No experience, since it doesn't get that cold in Tucson.

Chava


I always use the 10% ethanol blend and never have to add gasline antifreeze. It's cheaper that way too .

Cool "Welcome to Siberia Dakota" Hand Luke


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