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Gas tank full or partial over winter?

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Old 11-07-2018, 04:50 PM
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Gas tank full or partial over winter?

I know there have been threads on this before, but I thought I would seek out the current wisdom. Is it best to keep the gas tank full or partially full over the winter? I have heard it is best from both sides. I use non-ethanol original gas and try to start the truck every few weeks (only run on the road before over-salting of streets starts) and put in a partial can of Seafoam motor treatment. Is it best to keep it full or not - does it really matter? What do you think?

Bruce
 
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Old 11-07-2018, 05:20 PM
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Totally full eliminates the possibility of condensation. Totally empty with the cap off also works, if it's inside.
 
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Old 11-07-2018, 07:26 PM
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I always figured it was better to keep it full to keep condensation from forming

 
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Old 11-07-2018, 07:54 PM
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I plan to fill mine totally up soon, so that condensation is reduced. As a bonus, I can siphon & use that gas if we lose power to run my generator. Won't need a bunch of gas cans laying around the garage all winter
 
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Old 11-07-2018, 10:23 PM
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Full,with stabilizer. Empty can allow surface rust to form. No reason for Seafoam, IMHO.
 
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Old 11-08-2018, 02:37 AM
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Originally Posted by CBeav View Post
Empty can allow surface rust to form.
Gasoline tanks have a lead/tin coating to help prevent rust and corrosion from gasoline. They are not galvanized or zinc coated. Diesel fuel tanks are not coated.

 
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Old 11-08-2018, 04:02 AM
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No, there's no benefit to a half full tank. One reason is because vintage trucks have a vented tank, it is open to the atmosphere. Humid air is drawn into the tank at night and due to temperature changes throughout the day condenses on the inside walls of the tank and eventually into the fuel, a lot of water can build up this way. Soon the fuel separates into layers. Gasoline turns stale and degrades a lot quicker if there's only a few gallons in the tank, all the good stuff evaporates out. The tin-lead coating on the inside for rust protection is called Tern and if I had to bet, the reproduction tank manufacturers don't use it anymore.
 
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Old 11-08-2018, 07:59 AM
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I keep my carbureted vehicle with vented tank in a detached unheated garage every winter. Temperatures here sometimes go as low as -20 degrees. I park it at the end of October and start it again sometime in April the following year. I used to put a gas stabilizer in the tank but decided it isn't needed. It doesn't seem to matter whether the tank is full, half full, or nearly empty. I do keep a solar powered battery charger on it during the winter and put fresh gas in it as soon as possible in the Spring.
 
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Old 11-08-2018, 09:02 AM
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I'm in the performance gasoline business and have been for more years than I care to remember. I tell people who ask this question either all the way full or all the way empty. I'm not convinced over a period of three or four months there would be significant temperature changes in the winter to cause enough condensation to phase separate the gasoline if you are using an ethanol enriched gasoline. In most cases temps don't move quickly enough to cause much condensation to form. If you are using a non ethanol gasoline the issue of phase separation is a non issue and you only need to worry about the gas degrading. Most street gasoline if kept in a somewhat sealed tank and kept away from UV light should last through the winter with out much issue. There are storage fuels on the market and available that take all of the above mentioned issues out of the thought processes. Museums and car collectors tend to have their vehicles sit for extended periods of time and fuel becomes an issue. Price on these storage fuels can be an issue for some but shelf life on these fuels can be several years with no real degradation.
 
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Old 11-08-2018, 09:08 AM
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Originally Posted by Mixer man View Post
Gasoline tanks have a lead/tin coating to help prevent rust and corrosion from gasoline. They are not galvanized or zinc coated. Diesel fuel tanks are not coated.
Yeah, but eventually that wears away. There must be a lot of rusty tanks out there otherwise replacements wouldn't be so readily available.
 
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Old 11-08-2018, 09:57 AM
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Originally Posted by Dangeruss View Post
I'm in the performance gasoline business and have been for more years than I care to remember. I tell people who ask this question either all the way full or all the way empty. I'm not convinced over a period of three or four months there would be significant temperature changes in the winter to cause enough condensation to phase separate the gasoline if you are using an ethanol enriched gasoline. In most cases temps don't move quickly enough to cause much condensation to form. If you are using a non ethanol gasoline the issue of phase separation is a non issue and you only need to worry about the gas degrading. Most street gasoline if kept in a somewhat sealed tank and kept away from UV light should last through the winter with out much issue. There are storage fuels on the market and available that take all of the above mentioned issues out of the thought processes. Museums and car collectors tend to have their vehicles sit for extended periods of time and fuel becomes an issue. Price on these storage fuels can be an issue for some but shelf life on these fuels can be several years with no real degradation.
Great input! Thanks, Dangeruss.
 
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Old 11-08-2018, 12:33 PM
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Like Vern said.....I haven't noticed anything with my trucks being put away......with full .... empty.....or half.....I do add stabilizer to the fuel....also if we have a nice dry sunny day during the winter months they do go for coffee......
 
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Old 11-08-2018, 12:34 PM
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Originally Posted by abeagle View Post
I know there have been threads on this before, but I thought I would seek out the current wisdom. Is it best to keep the gas tank full or partially full over the winter? I have heard it is best from both sides. I use non-ethanol original gas and try to start the truck every few weeks (only run on the road before over-salting of streets starts) and put in a partial can of Seafoam motor treatment. Is it best to keep it full or not - does it really matter? What do you think?

Bruce
NO. It doesn't matter. And Condensation in fuel tanks IS A MYTH. The Myth of Condensation in Fuel Tanks by David Pascoe: Boat Maintenance, Repairs and Troubleshooting

Gasoline sitting for only a year isn't really a problem either........ but if you're worried, just drain it all out and park the truck.

DO NOT "start the truck every few weeks" unless you're planning to run it long enough to get up to normal operating temperature. That DOES cause condensation in the crankcase that is not removed in the oil until it gets fully warmed up. If you're going to start it, drive it for at least an hour or so. Running an engine for several minutes or even an hour at idle doesn't fully warm the engine or oil and fills the exhaust system with water vapor that just rusts it out faster.

Seafoam (and other Snake oils) are just Naphtha and light mineral oil. I am skeptical claimed benefits mixing it with gasoline. Mixing any oil into gasoline is a recipe for detonation in high compression engines.

The best thing to do if you're not going to drive the truck (and it sits out) would be to change the oil and filter, drain the tank, "fog" the engine and put the battery in the garage on a "Battery Minder."
After draining the tank, remove the fuel filter and run it until the engine quits. Right before the engine quits due to fuel starvation, use a marine Fogging oil sprayed into the carb intake. I think Seafoam has a Fogging oil as do others.

If it sits in a garage, change the oil and filter, either drain the tank or not, disconnect the fuel supply and run the engine until it quits (empty carb bowl), disconnect the battery and connect a Battery "Tender"........AND DON"T start it until you're ready to drive it.

Cheers,

Rick


 
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Old 11-08-2018, 03:02 PM
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Originally Posted by HT32BSX115 View Post
And Condensation in fuel tanks IS A MYTH
Sadly, it is not. Vintage cars and trucks have metal fuel tanks, not plastic or fiberglass. And they are vented. It is more of a factor when stored outside and/or in direct sunlight. And it is regional. Utah or Arizona isn't going to be a problem. A near empty tank acts almost like a bellows and is boiling off the good stuff and drawing in humid air and other contaminates.

Gasoline is actually blend of many different distillates and the light ends are driven off first. I agree with the rest of it mostly, starting an engine in the wintertime to idle a few minutes isn't helpful. For collector cars, Marvel's in the gas & oil is a longtime proven remedy for sticky rings, valves, lifters, vapor lock & carburetor troubles &c, particularly due to old stale fuel varnish, carbon & gum, and it can't hurt anything. Bent pushrods are the classic way to see what varnished fuel can do to an engine.

One thing they used to do is put a drain petcock at the lowest point of the fuel tank. This is a good modification if not present. Water and other contaminants will sink to that point, and being able to draw off a sample is good preventive maintenance. Check for good color and off odors. Bad gasoline is NASTY stuff, you don't want it in your engine.
 
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Old 11-08-2018, 03:51 PM
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Originally Posted by Tedster9 View Post


Sadly, it is not. Vintage cars and trucks have metal fuel tanks, not plastic or fiberglass. And they are vented.
So are aircraft fuel tanks and nearly ALL marine fuel tanks. In 40 years of working on aircraft, many that sit outside, I have never experienced condensation inside a tank. There were plenty of leaks in heavy rain but no condensation on the inside. IMHO, this one is right up there with batteries mysteriously discharging faster if left sitting on concrete.....

If you read David Pascoe's great article, you might notice that even if it is possible to condense ALL the water in air (at 50 degrees F) the amount of water that could form would be on the order of a fraction of a teaspoon.......
At 50F, an empty 200 gallon tank could contain 12.92 grams of water vapor, or 0.46 oz.
An empty 20 gallon tank could contain 10% of the above 0.46oz of water in vapor form. That would be 0.046oz of water (or about 1/4 TSP)

Even if it's possible to get all that water saturated air, I'm not really worried about 1/4 tsp. You're more likely to get water from refueling in the rain, or from your fuel supplier.

I am totally in agreement about losing higher end hydrocarbons in UN-vented tanks. One more reason to drain it completely, burn it in other vehicles or equipment etc, and fill up when you start driving "next Season".

Todays gasolines are lower vapor pressure mixtures now (7psi Cal-Reformulated for example) so higher end "boil-off" is not as bad as it was in the past, and newer EFI cars have slightly pressurized (un-vented) tanks and EFI that doesn't have near the problems starting with low vapor pressure gasoline as carbureted engines like our old trucks have.
It's more important to get as much fuel out of the carburetor as you can in an engine that sits for a long time to prevent drying out and leaving deposits.

I really like the idea of adding a "quick-drain" at the bottom of the tank
 


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