To Fill or not to Fill

2021 Ranger 521L
Mercury 300 Pro XS (2B781704)
What are most doing with regards to fuel in tank for winter storage. Would it be better to fill tanks or just leave as is and add stabilizer.
Boat is stored in heated garage.

Either works.

Mine is stored in my heated garage and I run the tank is empty as I can so it is mostly as fresh as possible in the spring but I do treat it also the last time or two out

Mine is stored in an unheated pole building full tank with the recommended cocktail - always.

I store all my boats inside an insulated but non heated garage full of fuel also with Don's cocktail added. I heat the garage only when I pull one of my vehicles in for servicing during the cold winter months. I have never had a problem by operating in this manner plus I use non ethanol gas in them and anything else sitting for weeks at a time without being cranked.

Either empty OR full. EITHER way you should have it well stabilized before putting the boat up (and have ran the engine on the water with the stabilizer in it).

If storing with a full tank, consider the length of time you will store it and whether it might be prudent to consider the age/octane of the fuel come spring.

Appreciate the responses. Thanks to all that replied.

As others have stated, I think either way is fine...for the most part. I've gotten advice both ways from knowledgeable mechanics. The circumstances of condensation forming on the unfilled portion of the fuel tank is what concerns me. In my unheated garage, fluctuations in temperature and humidity could certainly cause condensation resulting in water entering the fuel supply. For this reason, I've taken the approach of filling my tank. Using the approved cocktails (QuickStor at end of season, Quickare every other fill-up) the fuel should remain stable during the 6 months or so that my boat isn't being used. If I was putting it up for a longer term storage, I might rethink the approach.

Another consideration, in these times of economic uncertainty, wars, general SHTF worries, is to keep your tanks full on boat, other powersports equipment and vehicles. You never know when you might need it either in that vehicle or to drain for use in your car/truck, generator, etc!

I think what you are doing should be fine, especially if the fuel is non-ethanol. Most boats built in the last 8 years do not have externally vented fuel tanks, so the risk of condensation is significantly less (not zero but less). The valves will let some air in if there is sufficient negative pressure in the tank (like when you are using fuel).

FWIW, I have stored full (freshly filling the tank just before storage) of quality (BP) Non-Ethanol Premium 93 Octane (to allow for some octane degrade over the 6 months of being put away) unleaded with Quicklean and Quickstor at the bottle recommended dosage every winter for 6 years now, and no fuel related issues. I choose this method to combat/prevent the aforementioned condensation issues.

I always run Quicklean and Quickstor all summer at the bottle recommended dosage as well...

All the 1yr/100hr and 3yr/300hr maintenance performed just prior to storage as prep at my Merc dealer with their "Winterization" which is spot on for the 1yr/100hr and 3yr/300hr services...including hitting the cylinders w/ StorageSeal...
Except I always change the plugs every 3 springs, after storage, and after the first run of the year to burn out the storage seal...and have fresh plugs in.

Usually the tank of over-winter fuel gets all burned in my week long Ontario fishing trip 1st week of June. Sometimes if we have a nice spring, it gets burnt before we go.

Here in LA I store mine from June to October..not a fan of heat. I use 87 non ethanol and use Don's cocktail at each fill (including quickstor) with an added dose of Startron. I run my 26 gallon tank to about 3 gallons before storing and add about 18 gallons in October when I start back up. I change all the criticals before fall boating ( oil, filter, fuel filters, lower unit lube). Exception being spark plugs...they change at 2 years. I launch by myself and float my boat off and it fires every time.