Store with full tank or empty?

[Bonnewagon]

Myself, I usually store a vehicle over the winter with a full tank of gas. Plus I add some Store-N-Start additive. That works fine if I am using the vehicle now and then, or it only sits over the winter. Nowadays I might go a full year without emptying a gas tank so the gas can be quite old.

My question is this: If our G-bodies are a sealed system, sealed gas cap, with no vent to atmosphere, can't they be left empty over the winter or longer? With no vent, there is no way for moisture to enter. It won't 'breath' like an open system thus keeping moisture out. The only opening would be the charcoal canister and that is far away from the gas tank. Would that keep moisture out? I guess if the vehicle gas tank was slowly run down during hot humid weather, there could be much moisture entering the tank . But what if the tank was siphoned down all at once during cold dry weather? What would go on with an empty tank? No fuel pump in the tank, so that is safe. The gas gauge sender? Submerged or dry? Does the gas cap 'breath'? How does air replace the gas? Canister, or gas cap? This driving me bonkers, please set me straight!

 

[Supercharged111]

I feel like ethanol content is the far bigger concern here, correct me if I'm wrong.

 

[Clone TIE Pilot]

I feel like ethanol content is the far bigger concern here, correct me if I'm wrong.

With a sealed Evap system, even ethanol gas should not phase separate for a year. Still I would add Stabil 360 as that is made for ethanol gas.

 

[Bonnewagon]

I asked my enginerd cousin about this. He feels a full tank with a fuel stabilizer is the way to go. Here is what he said:

"Rule of thumb is; storage for up to a year or a bit more, add in a Pint of Sta-Bil or mineral spirits then immediately fill it to the top and a bit more. The treatments alter the fuel’s RVP so that as barometric pressures change over time, the fuel won’t off-gas (evaporate), keeping system pressures very low so the vapor canister can ingest any fumes."

"Now, there is really no fully sealed fuel system, nor does an “empty” tank exist. There will always have enough static fuel pressure to overcome the spring-loaded valve on top of the canister.
And even if you “syphon” your tank “dry”, there will be fuel left inside. So, think of it this way; any fuel left will begin to evaporate and raise system pressure. With a large volume of air relative to the fuel, the gas will “go bad” much faster. Varnish.
All because of changing atmospheric conditions; barometer and temperatures. A full tank, right to the top, is less likely to be affected by these things, if at all."

Makes sense. But what I do with lawn mowers, pressure washers, etc, is to run them totally dry, clean the spark plug, then put them away. Next Spring I just add gas and go. They always start right up. Most have plastic tanks that don't rust. Our cars have steel tanks that will rust. The outside is terne plated [lead], what about the inside? I guess for over one winter a full tank makes the most sense. But for really long term storage I would still prefer a totally empty system.

 

[Sweet_Johnny]

I think a full tank with stabilizer is the way to go to avoid the tank rusting from the moisture in the air, even if sealed. You mention the charcoal canister... I'm not sure our system is ever 100% completely sealed- my EVAP canister has a vent to atmosphere that seems open all the time, at least under pressure. I don't know if it closes in the absence of pressure though, but that would make sense. I just found this out due to overfilling my gas tank which led to a charcoal canister full of gas that needed blown out. There's also the filter, and I don't know if there's a check valve or anything to seal air from entering/ exiting without engine vacuum. I don't know anything about charcoal canisters aside from filling them up with gas...

 

[CopperNick]

Unless you can do something along the line of pouring in a pint or two of light oil that will float on the surface of the gas and then draining the tank slowly somehow so that the oil clings to the inner tank wall surfaces, my vote goes with the full tank and the Stabil. Even if the tank isn't all that full, add the Stabil and then run the engine for a few minutes, if you can, to get the stabilizer completely through the fuel system and up into the carb or injectors.

The only other way I know of would be to drop the tank out, and then remove the sending unit and pump/drain the tank completely dry. Then use compressed air to try and dry out the inner tank walls and floor. After that spritz in some Deep Creep or similar to coat the metal against moisture intrusion and put the tank somewhere dry and off the floor; bag it or wrap it in heavy plastic maybe. This whole suggestion is a lot of work and not apt to be simple to accomplish.



Nick

 

[Clone TIE Pilot]

I think a full tank with stabilizer is the way to go to avoid the tank rusting from the moisture in the air, even if sealed. You mention the charcoal canister... I'm not sure our system is ever 100% completely sealed- my EVAP canister has a vent to atmosphere that seems open all the time, at least under pressure. I don't know if it closes in the absence of pressure though, but that would make sense. I just found this out due to overfilling my gas tank which led to a charcoal canister full of gas that needed blown out. There's also the filter, and I don't know if there's a check valve or anything to seal air from entering/ exiting without engine vacuum. I don't know anything about charcoal canisters aside from filling them up with gas...

The whole point of any evap system is to capture evaporates emitted by the gas tank while the car is park. This is a major source of pollution from ICE powered vehicles and the reason for visual inspections. Then the captured evaporates are purged into the engine when its running. There is a one way valve but it only works for gasses, not liquids. Even modern enhanced evap systems can be saturated by fuel tank overfilling.

 

[Bonnewagon]

I guess I will stick with the full tank/stabilizer plan. But stuff I store for a LONG time I will empty completely and store dry. I just have to be careful and watch the time. I once left treated gas in a Trans Am for WAY too long. It caused the valves to stick open and lots of backfiring. The gas was mostly gunk and I was not smart enough to get it running first with an outboard motor portable gas tank and fresh fuel. It took me forever to let it idle and loosen up. Days in fact.

 

[69hurstolds]

There's two kinds of fuel treatment for the ethanol fuels that I've used that actually works well IMO. That's the aforementioned Sta-bil 360 and the Ethanol Shield. Both work the same, IMO. They also cost about the same to purchase.

The only difference is that the recommended amounts are higher on the Ethanol Shield (1 oz. per gallon) meaning you'd have to pump in 15-16 oz. or so into your G-body tank when storing. Whereas the Sta-bil 360 you use typically 1 oz per 5 gallons of fuel. Meaning much less, at only 3-4 oz per tank give or take. I'd also add it to any fuel cans you got sitting around, but usually I just pour that into the Ford to empty them out during the off season.

If you buy non-ethanol gas and don't need the 360, then I'd still use the regular junk. Better safe than sorry. I don't know if you can mix and match the Sta-bil products depending on ethanol or non-ethanol gas, though.

There's also this "engineered fuel" I was thinking of trying for the lawn mowers but it's rather pricey. Called "Tru-fuel" for 4 cycle engines. Just run out most all your ethanol gas in the mower, pour this in and run it a bit and store your mower and it's supposedly good for up to 2 years. The unopened can is good for 5 years. The local Home Depot normally sells it for 24 bucks for a 110 oz can, but it's on sale right now for $9.88 per 110 oz. (almost a gallon). People that have used it think it's the cat's azz. But again, I think it's sorta pricey. But, you do you.

 

[pagrunt]

There's also this "engineered fuel" I was thinking of trying for the lawn mowers but it's rather pricey. Called "Tru-fuel" for 4 cycle engines. Just run out most all your ethanol gas in the mower, pour this in and run it a bit and store your mower and it's supposedly good for up to 2 years. The unopened can is good for 5 years. The local Home Depot normally sells it for 24 bucks for a 110 oz can, but it's on sale right now for $9.88 per 110 oz. (almost a gallon). People that have used it think it's the cat's azz. But again, I think it's sorta pricey. But, you do you.

This is what I've been running in Jr.'s Monte to move it around the house & to allow it to sit without running for extended periods. Was in the car last winter & with typical requied steps fired right up this past spring. Lowe's used to sell it in the quart cans (which I bought up on clearance) but now only in the 110 oz can. I use the 2 stroke fuel in my yard tools too.