Fill Gas Tanks Up Or Not ?

Not really any need to fill up but do use a fuel treatment, we use Seafoam but others are fine too. I for one have fuel readily available all over my lake so I never have more than a half a tank in both tanks. This saves weight and improves performance while increasing gas mileage.
 
Fill tank and I use Sea Foam. $5.99 can at local gas station.
 
Been doing this for a long time...Stabalize what ever fuel is left in the tanks. Replace water separators after first run. NEVER had an issue. IMO, filling is over rated.
 
Always filled mine with stabilizer for 2 reasons: 1- less chance of condensation. 2- had an insurance guy require it (not my boat) to reduce gas vapor if stored indoors. JMHO.
 
40 plus yrs in the petroleum business. Don't waste your money on fuel additives they are all snake oils! Ethanol bases fuels love water and or condensation. Keeping your fuel tanks at 90 percent at end of season will eliminate any problems. I have had to treat underground fuels tanks that came in contact with water too many times. Prior to ethanol in the fuel, condensation and water would drop to the bottom of the tank and could easily be removed with a pump. This is an awful fuel and the oil industry hates it! Sorry for not being politically correct. End of rant!
 
... For reference both watercraft are stored right where Ala, MS & TN Meet

You must be close to Aqua Yacht Harbor Marina, where I keep my boat. The fuel there contains no ethanol, but does have fuel stabilizers in it. Just fill up. Doesn't hurt to adc Sta-Bil, but no need since it's already in there.
 
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This end-season I asked this question to 3 highly respected mechanics in the great lakes area. One said fill it and use stabil. The next said fill it half way and use stabil. The last one said store it almost empty and use stabil. So, I dont think it matters, but Stabil was the common thread in all methods.
 
This end-season I asked this question to 3 highly respected mechanics in the great lakes area. One said fill it and use stabil. The next said fill it half way and use stabil. The last one said store it almost empty and use stabil. So, I dont think it matters, but Stabil was the common thread in all methods.

2 out of 3 were correct.

Here's the thing. Condensation is real. It is not a made up thing, it's not magic and it does happen. But, there are many variables that determine whether or not it will form. How quickly the temperature swings is one of the main factors. The tank, itself, where no fuel is, will change temperature faster than the fuel inside (I'm sure there's a better scientific explanation to this than what I am providing). That can equal condensation. It's hard to physically see this, given where the tanks are located (and that it's on the inside) so some people will refuse to believe it if they can't see it. Bad idea. What IS easy to see, though, is condensation that forms on your engine. I can't even count the number of times I've seen this. For someone to think that gas tanks are somehow immune to this, well... maybe they would be interested in buying that plot of land I have... unseen.

Boat fuel systems are also MUCH more open to the environment (until just recently) than in a car. Another factor is the tank material. Plastic tanks are less susceptible, although not immune, than aluminum. Whether or not leaving a tank half full has "worked" for someone in the past, does not necessarily mean it will work in the future nor does it mean it will work for everyone. Remember, there's lot's of variables. It could be that for the person who is leaving the tank half full (and is also using appropriate additives), they are indeed getting some condensation, but the additives are doing their job.

And, do we need to talk about Ethanol and what it does and how it can pull moisture from the air? I think we're all pretty much in agreement on this is terrible fuel, for more than just that reason.

In the end, hey, everyone can do what they want - it's their option. But condensation is NOT fake. It does happen. If you're on the fence about it, think about it this way... What does it hurt to fill it up? Completely emptying is not feasible for most of us, unless you have portable tanks. If there's even a possibility that condensation will occur, filling the tank dramatically reduces that possibility, or at least lessens the amount of water that gets in the tank. The stabilizers we have available nowadays are very good. They will easily keep the fuel good until next season, and really, even longer.

What's the downside to filling it up? Is there more or less of a chance of getting water in your fuel if you fill it up?
 
Startron !!! - recently got a large bottle of it (qt?) on Amazon for decent price. I use it for all my gas engines.
 
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I put a gallon of Seafoam in my 100 gallon tank and fill up it…so far no problems.

Condensation? How much exactly does a tank breathe, how many cubic feet of new air is moving in and out of your tank…I dunno, I don‘t think much in storage. I do know that on my little 100 gallon tank, if it was totally empty, potential condensate at any time could be measured in fractions of teaspoon.

Ya condensation is a ‘real thing‘. I think one of the contributors to fuel/fuel storage/winter layup problems is the fact that condensation and other ways of accumulating water is a ‘year around thing’. Those that have spring start up problems, phase separated fuel, are probably not just dealing with the winters accumulation of condensation.

What will help? Good quality fuel to start with, don’t leave your tanks empty all boating season, use your boat/run some fuel through it. In a way what we don’t like about ethanol actually helps get rid of the water as long as you burn some fuel. So there’s an excuse to use our boats more….we could call it fuel tank maintenance.:grin:
 
Your tanks breathe all the time, anytime the atmospheric pressure changes....you ought to know that. The only way to prevent it would be to seal them, or fill them.
I do know that. Adjusting to changes in pressure or volume is one thing. The question is on air exchange....how much is there? How many cubic feet of new air and it's associated water vapor is the tank subjected to? I don't think much in storage.
 
I filled mine up with 48 gallons of ethanol free gas and added Marine Stabil. To me, it's not worth the risk even if the chance is small. It's not like I won't use the gas next season.
 
I saw this in the manual the other day... Just to throw in Merc's perspective

image.jpg
 
Thats exactly what my manual said, so thats what I did, I made sure.my last tank had the recommended amount of seafoam to run through the system, there is still some in the tank. I taped over the vent to try and help condensation issues. It has a plastic type tank. I am tempted to try to drain it completely before the.first fill. We'll see in the spring, soon, I hope.
 
Not to put a twist on this thread, but how does this all apply to diesel fuel tanks, and what are the recommendations for diesel.

---fill 'em or leave 'em near empty?
---fuel additives or not?
 

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