full tank = less room for air space which means less room for condensation mercurys fuel stabilizer will help with phase separation steve snider got it part right but he failed to mention that during phase separation you end up with three layers in your tank....fuel on top pure alcohol in the middle and water on the bottom.

I always run in to empty, and then use both stabil, and the ethanol treatment. haven't had a problem yet, knock on wood

It seems like it depends on what style of boater you ask, Most of the high performance boaters seem to run it low with treatment, Here are two other poll's for this same question from preformance boaters to look at.
http://www.performanceboats.com/html...ad.php?t=49941

http://www.speedwake.com/upload/show...threadid=62666

Then if you ask the none performance boaters, Most of them keep them full with stabilizer, See this poll also.
http://forums.iboats.com/showthread.php?t=358698

Also Bob Teague wrote this in power boat magazine
February 2009 Teague on Tech.

SETTLING THE DEBATE

Question: Thanks for all the great advice. I utilized your insight on a past issue for fogging fuel-injected engines. I fogged my MerCruiser 502 Magnum engine with Marvel Mystery Oil dispensed from a garden sprayer.

My friends and I, all owners of performance boats, debate regularly on whether to leave the fuel tanks low when winterizing or fill them up to minimize condensation. We all agree to put stabilizer in. I subscribe to the theory that there is nothing better than fresh gas when starting up in the spring. I usually dwindle the tank down to less than a quarter tank. My friends don’t necessarily agree with me. Can you settle our debate?

Kris Lukowitz
Sayreville, N.J.

Answer: The concept of filling the tanks to minimize condensation during storage was the standard procedure in years past. It is still common practice on airplanes. The problem is that most automotive gasolines purchased at the pump today are not the same quality as they were when it was common practice to fill the tanks prior to storage.

It is likely that your fuel also contains oxygenating components such as ethanol, isopropanol and ether that are currently used to replace MTBE. These additives are injected into the fuel during the reformulation process. Ethanol, isopropanol and ether are polar solvents, which means they are water-soluble. When they are present, condensation can be absorbed into the fuel resulting in further deterioration. The components added during the reformulation process also have the tendency to evaporate more rapidly than the base gasoline, which has the same effect as lowering the octane rating.

Aviation fuels are required to be higher quality and do not deteriorate rapidly, so it makes sense that filling the tanks on airplanes is usually the practice.

I used to believe that leaving the tanks full of fuel was the best practice. About five years ago, I switched to leaving them as low as possible as a result of tests that we performed on fuel to see how it held up during long storage periods. The bottom line is that modern pump gasoline tends to get stale faster than we imagined.

When you bring the boat out of storage, I recommend filling the tanks with premium gasoline. Using the higher-octane gasoline will improve the overall quality of fuel when mixed with the existing fuel in the boat’s tank(s). In addition, using a quality fuel stabilizer can’t hurt. In short, you win the debate.

– Bob Teague is Powerboat’s lead test driver and a columnist for nearly 40 years.
http://www.powerboatmag.com/february-2009.html

http://www.teaguecustommarine.com/

ON E with a full bottle of Marine Stabil.

I have not looked into the contents of Stabil so it may be great. With that said, make sure you use a NON-alcohol stabilizer. It should say alcohol free on the label somewhere...

I use AMS Oil Fuel Stabilizer but I do know the Merc stuff is NON-alcohol as well. Don't forget about all your other toys that have engines.

I don't winterize the boat but I do use it in generator and compressor. Works well. A year is about max comfort level for me. Never leave anything full long term with Ethanol. Today's pump gas sux.