Our 10/17/2012 post “Putting Your Boat to Bed” generated many conversations regarding fuel in the tank. I asked Columnist and freelance writer Captain Fred Davis to review the subject and here is what Captain Davis reported.
I’ve spent quite a bit of time researching and reviewing the topic regarding fuel in the tank your bloggers inquired about. I’ve talked to chemists, fuel company reps and other experts.
Oil company reps suggest your fuel tank should be filled to around 90% after treating with a marine stabilizer. It’s best to replace the water separator filter just prior to stabilizing the fuel. When adding the stabilizer, (Sta-Bil or StarTron additives work well), be sure you use marine grade which is twice as strong as the automotive mixture. Do not skimp on the stabilizer; it will do no harm if you use extra. Be sure to run the treated fuel completely through the entire system.
Now the controversial questions: Why not drain the tank, leaving it near empty? Or, as some suggest, why not “leave it half-full” so you can add a half tank of fresh fuel next season?
Ethanol is an alcohol; it absorbs moisture during the season. The water, mixed with the ethanol will pass through the system and burn with the mixture. While in storage, the fuel starts to break down in approximately 30 days. Once the alcohol absorbs enough moisture the breakdown separates leaving a thick content at the bottom of the tank. Absorption takes place as the moisture in the tank, having entered through the vent, exceeds a certain point causing phase separation to occur.
If the fuel tank has more air space it can circulate more moisture, which expedites phase separation. Less air space means less moisture and therefore, if the tank is 90% full there is still enough room for expansion as the tank warms from the sun shining on the cover or as warmer air temperatures circulate around it.
There are opinions put forth that emptying the fuel completely is the best action. Actions, such as using a shop vac may prove dangerous. In many states, Fire Marshals prohibit storing a boat with an empty fuel tank. An empty tank could be considered a bomb because of the danger of fumes.
Sea Foam is my additive of choice. Has been for years.
Yes there are additives for diesel as well and do the same job or better. I wont be worring anymore since I lost my 43′ Egg Harbor in Huricane Sandy. It sank with twinn 6-71 Detroit deisels,
Is Marvel mystery oil considered a good fuel stabilizer? will this product prevent phase separation?
Im not sure butI wouldnt why not check with the MFG?
Great advice. I use Sierra and Lucas ethanol additives but they are very expensive. Don’t be afraid to add a little extra. 1 oz treats 10 gallons.
full tank is best in anything you have car. mower. mc. boat. marine stabilizer is the best have done this fore years ben a mach for 30 years
This article talks about storing a gas powered boat. What is the recommendation for diesel?
With diesel fuel top off fuel tanks and add Biocide. Do not drain fuel lines or run engine out of fuel. Fog the intake on diesel engines.
My boat stays in the water year a round (Galveston, TX area). The boats sits for long periods of time between uses. There are additives on the market called BioGuard or BioBoard. Are these any different than a Stabil additive?
Another good reason NOT to use Ethanol added fuel in any boat. How about advice for those of us who don’t?
What about boat motors that run marine (non Ethanol)fuel?
What if you use what is sold as “ethanol free” gas from marinas? I live in S. Louisians & all marinas in my area advertise ethanol free gas. If there still truely ethanol free gas, or is it that they don’t have to state it has ethanol if the percentage is less than 10%????
the recommendation of stabilizer
in gas goes way back to before
ethonal
What about diesel?
What if you use ethanol free, or pure gas? That topic seems to be missing form this conversation. Thank you.
1-I assume you are talking gasoline and not diesel. You never identified which you were talking about.
Yes, gasoline.
Good advise, but does the same apply to diesel?
Thank you for the info this has been a question of mine for along time . What do you recommend staybil or seafoam for the fuel tank . I have a 90 hp Honda on my boat with a 12 gallon tank . Thanks , Scott ( Michigan)
Great Information! How about a story on Diesel fueled boats?
Why not install a quick drain in the bottom of the fuel tank and drain out what ever seperation there maybe after the winter season is over. Water is heavier than fuel. General Aviation aircraft do this all the time prior to each flight.
Nitrogen is cheap. Take N2 purge the empty tanks. Leave an N2 blanket in the tank. N2 not only keeps a tank safe from an explosion or fire, but it also dries the moisture in the space. N2 is an amazing gas to use. Just my opinion.
Please help me. I have a boat that has been in storage with a full 2 tanks for the last 6 years, and I’m afraid to run the engines with this fuel in it. What should I do? If I need to drain the tanks and refuel, who does that? My boat is at Great Oak Landing in MD. Please help as my husband passed away and left me with this situation and I don’t know what to do. I don’t want to sell my 3807 Carver cause I love boating. But, I know something needs to be done. Maybe I should just run the bad fuel out??? HELP!! Thanks, Eileen
Do NOT run the old fuel thru the engine. There are many safe ways to get the fuel from the tank. In an open, not pressure tanks after 6 months gasoline starts to loose much of its octane. Contact the storage facility and ask if they know of someone who can remove and clean the system.
sorry to hear of your loss
i suggest you have your marina
take care of your tanks. dont
just run them out
How about Diesel?
Additives or not, full or not?
bio cide is reccomended for
diesel and yes a full tank
I take it this applies to gasoline engines/ tanks, not diesel. There is no alcohol additive in diesel.
your correct