Fill it or not

[Tom7227]

I have a Crestliner pontoon with a built in gas tank.  The manual for the boat said that the 17 gallon gas tank should be filled in the fall.  I have done that and used the non-oxy gas and stabil.  When I first got the boat it would go 22 miles per hour in calm water.  Now the best it will do is 19.3.  I think a major factor is that the gas sits over winter.  I don't use the 17 gallons until very late in the year, in fact I haven't used it all for the past couple of years.  I store the boat in an unheated pole barn up near Stacy MN.

Should I fill the tank or not?  If I don't what are the downsides?  I assume condensation but I wonder how much that will be and whether it is a big issue given the use of stabil.

Thanks for your time.

Tom

[Ufatz]

Dump in a bunch of Sta-Bil.  Then fill the tank right up to the top,   where you can SEE the gas (if possible) and call it good. It is better if you can run the engine for a short period to make sure the Sta-Bil is getting into the fuel system so it is laying in the lines and carburetor (assuming you have one) or injection system.

Nuttin' to it.

[delcecchi]

I have thought about the condensation issue and even did some calculations.  I have decided it is not a significant problem, at least here in Minnesota.

But gas getting stale is a problem I know people have had.   The Techs that winterize my motor said to not bother with filling the tank, but just put in fresh gas in the spring instead.  So I just store it with whatever the amount of gas happens to be.  

My buddy who has a 70 Suzuki 4 stroke on his pontoon has noticed that stale gas in the spring makes the motor run bad(ly). 

[CaptainMusky]

My boat has a 41 gallon tank. rarely is it ever full and I will never leave it over the winter with a full tank of gas.

Here is what I do. When I know I am getting to the last few uses of the boat for the year I will make sure I have at least a half tank of non-oxy gas and pour in a full bottle of sea foam. No stabil for this guy. Stabil has a shelf life of like 3 months so who knows how long it has sat on the store shelf before you purchased it.

Sea foam has other benefits and a fuel conditioner and system cleaner. Win Win.

Come Spring when the boat comes out the tank is then added to or topped off with fresh non-oxy gas.

Ive been doing this for 20 plus years with various boats, snowmobiles, etc and have never had a fuel system related issue.

 

[Mike89]

captain musky does pretty much what I have done for over 35 years and yes with sea foam. 

[PurpleFloyd]

I look at it this way. People started using heat/isopropyl in their gas originally as a way to bind water that is in the gas an prevent it from freezing. When they started to add ethanol it served the same purpose. The only time it becomes a problem is if there gets to be more water through condensation in the gas than the alcohol can absorb but if that happens, having no ethanol/alcohol in the gas doesn't fix or make it better. The problem is water and filling it with gas eliminates the chance of condensation and thus you should not need to add products like stabil or Sea Foam. 

Sea Foam contains like 20-25% alcohol itself so if your concern is the ethanol in the gas this is no cure for that part. The rest is just petroleum based solvents that can dissolve buildup but you can get Naptha or other products from a paint store much cheaper to do that job. 

If I had to pick one method that would be bulletproof it might be to fog the motor with any sort of product you felt comfortable with and then drain the tank completely and leave it dry over the storage season. Obviously any moisture in a metal tank can cause corrosion so make sure it's dry. Then, prior to the next activity, verify the tank is clean and dry, clean and dry it if it isn't and then fill with fresh gas before you use it. That way you know the tank was clean, dry and the gas is good. 

[delcecchi]

I think the gas tanks in most boats and pontoons are plastic these days.   I am pretty sure the one in my boat is and it is a 1998.   And the neighbors' pontoon tanks are plastic as well.    So rust is not an issue. 

The problem to be solved is that gasoline deteriorates in storage, with the RFG (reformulated gasoline) containing ethanol going bad faster.   That is why folks are getting away from filling the tank for storage.  

As for whether seafoam or StaBil or other products do much to keep the gas from deteriorating, that is an open question in my mind.   I haven't seen any tests from anyone objective, although I haven't looked very hard.   

I don't think condensation is a problem in the winter in our climate, since there just isn't much water vapor in cold air, especially below freezing. 

[BartmanMN]

How much extra weight have you added to the boat with Gear and dump?  That could take some top end off.

I doubt it is the gas.  I fill up my tank with non oxy and add the marine stabil at end of the season. 

Then it is ready to go for the next season,

 

[delcecchi]

Neighbor's 70 suzy four stroke on his pontoon has definitely had performance issues in the past when running on old gas in the spring.   Put some new gas in and it ran better.  

I have not noticed any such effects on my Suzy.  

Apparently gas will oxidize slowly even at normal temperature just from exposure to the air.   This oxidation produced gums and other bad stuff and degrades the properties of the gas.  The more sealed the container,the additives in the gas,  the temperature variation, and the temperature all affect how fast this process happens.