My gas tank is currently removed from my Monaco so I don't have to wrestle with how to prepare it for long-term winter storage. And I'm glad for that, because I've just spent an hour looking into that issue and I don't think there's a clear-cut answer.
A lot of advice says to fill the tank. That advice needs to be updated to take into account the ethanol in today's gas. I want a reality check on that advice for today's gasoline AND yesterdays steel gas tank.
Ethanol is a magnet for water, and there are too many arm-chair explanations as to why this will, or won't, be good for metal gas tanks. What is clear is that today's pump gas is not stable after as little as a month or two, hence the constant advice to add stabilizer, which is a whole other rabbit hole.
When you think about it, the metal gas tank "problem" is always there, on those summer days when you're driving the car and the 4 months (or more) in the winter when your storing it. And these are big gas tanks, and if you can buy non-ethanol gas it's going to be expensive to fill up. And you'd better hope you don't have any leaks.
I think the hassle of filling your tank with gas for long-term storage that you really don't know has or doesn't have ethanol and then adding a stabilizer is not worth it.
Since my tank is out, and at some point will go back in, I'm going to install a drain plug, so in the future I can drain it completely for storage. Then as a storage solution I'll find a way I can insert and remove desiccant material in the tank to keep it dry. Beyond that, something that can be done is to buy a tank of compressed nitrogen and use a long tube and flood the air space in the tank with nitrogen, displace the (presumed to be humidified) air in the tank, then put the cap on.
Other more practical things to look at if the car isin't going to be moving for a while:
- take the battery out, keep it somewhere that doesn't freeze, or probably best is room temp or cooler, put a trickle charge on it every once in a while. Check it with a volt meter, don't let it go below 12.25 volts if you can help it.
- I like the idea of putting a car on jack stands to keep the tires from getting flat spots. No hassle of having the check the tire pressure regularly for those problem tires with slow leaks.
- If the car is outside, then when it's dry outside, put an indoor car cover on the car and then throw a 10 x 20 piece of 6-mil vapor barrier over the car and tie it down with a few loops of 1/4" rope under and over the car (hood and trunk). Then let as much rain and snow hit the car as it wants.
