Fuel Preservative

[Wellardmac]

Bingo!

Remember to refill your tank if you take it out over the winter.

A tank that is less than 95% full has more oxygen in it and has the possibility of degradation of the additives (it's actually the additives that degrade in the fuel, not the fuel itself) - that degradation is what provides the possibility of gum formation in your fuel and leaving deposits on your injectors.

In terms of water adsorption, the head spaace in your tank also plays a role. Fuel itself does not absorb water (too hydrophobic - water hating). Unfortunately, the ethanol that is now added to fuel can absorb water. Thankfully it's only present in a few percent of the fuel. You have to ask where the potential for water exists... air fuel contact, or an open system. A sealed tank is not open and thankfully, Winter air is very dry, so the chances of water problems with fuel are minimal.

Now, all that being said, it's a totally different question for non-winter storage and that would be a very different discussion.