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I keep reading conflicting advice from experts about fuel level for winterizing. (All recommend adding stabilizer.)

1) Tank almost full. To inhibit condensation.

2) Less than 1/4 full. In case the gas turns bad and you need to drain it in the spring.

3) It doesn't matter.

Any thoughts?

Full and a new water separator/filter.

For our 2005 496 Merc Mag HO, the manual recommends filling to the top if using Ethanol free fuel to avoid tank condensation which can occur with large temperature swings like we have here in the NE (especially in the Spring).

If using fuel which contains Ethanol, the manual recommends draining the tank to as low as possible.

In all cases a fuel stabilizer should be used as per the manual recommendation.

We’ve never had any fuel issues after storing our boat in an unheated covered storage facility in Erie PA for the last 28 years.

Hope this helps.
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I leave it low, generally 1/4 tank or less and add stabilizer - non ethanol in my case. I would rather deal with a little condensation (which is really going to be minimal) than have a tank full of old fuel in the spring. That's what I do and never an issue in many years and many boats. My layup is 3-4mos here in NC.

As close to empty as possible. This year will be the first year I have ever added stabilizer.

AsLan7 wrote: ↑Thu Nov 16, 2023 7:43 am For our 2005 496 Merc Mag HO, the manual recommends filling to the top if using Ethanol free fuel to avoid tank condensation which can occur with large temperature swings like we have here in the NE (especially in the Spring).

If using fuel which contains Ethanol, the manual recommends draining the tank to as low as possible.

In all cases a fuel stabilizer should be used as per the manual recommendation.

Here in Minnesota most of our boats are in storage at least half the year, and Aslan's guidance seems to be pretty common around here. I haven't heard of many people having problems by doing the opposite of what's recommended if they use fuel stabilizer and run at least a full tank of fuel through the boat every summer, so don't sweat it whichever you choose.

jhnmdahl wrote: ↑Thu Nov 16, 2023 10:43 amHere in Minnesota most of our boats are in storage at least half the year, and Aslan's guidance seems to be pretty common around here. I haven't heard of many people having problems by doing the opposite of what's recommended if they use fuel stabilizer and run at least a full tank of fuel through the boat every summer, so don't sweat it whichever you choose.

Running at least one full tank through is the key.

Our channels in front of our houses were closed in the summer of 2022 so many people didn't put their boats in. Many people who didn't use their boats in 2022 had issues with their engines in 2023 and had to have their tanks drained of the nearly 2 year old fuel. The people that kept their tanks closer to empty had a lot less fuel to pay to be drained.

I made sure I ran my boat for 3 days in 2022 to go through the old fuel as well as running new fuel through the boat. I like having a 90% fresh fuel in my boat when I start out my boating season.