I would not fill the tank. I never add fuel to my tank for storage.
Filling w/ fresh gas for the first use is much better.
I personally would:
1. Drain fuel and use in auto
2. Mix a small amount of fuel and stabilizer to run the engine so the
engine has fuel stabilizer in it for the storage period.

The other option would be to just add stabilizer to the 40 litres of gas
(haul it around to mix it up good), run the engine to get the mix into it.

Fill w/ fresh gas when you are going to use.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com
"A.Z" wrote in message
om...
My question is about the effectiveness of stabilizer over a long
period of time.

My boat is normally stored from oct-nov to june-july. At the moment,
I have about 40 litres of 2 month old gazoline in the 100 litre tank.
Should I try to drain it and refill with stabilizer added to the gaz ?
Or should I just add fuel to fill the tank and assume that adding
stabilizer will properly treat all of the fuel for 8 months? The motor
is a 90hp Mercury 4-stroke.

AZ