To Store Your Boat With a Full or Empty Fuel Tank ?


Ethanol Gasoline :  From about 2005 we began seeing most of the fuel being an E10, or 10% alcohol.  This formulation is NOT good news for the boating industry/owner.  This fuel can effect the older rubber fuel lines by softening them, allowing them to collapse internally.  So you may need to replace your fuel lines with the newer alcohol resistant lines.   An interesting feature of Ethanol in gas is its cleaning ability.   It will over time remove all those old layers of varnish from previous gasoline which then gets deposited in the fuel filter, plugging it and anything that gets thru the filter ends up in the carburetor or injector making life miserable for the boat owner/mechanic.

Full or Empty :  The old word was that during the non running months, (usually winter) you need to top off your fuel tank to keep it from having a large void whereby condensation could form, creating water in your fuel the next spring.  Well there are other variables relating to issues of concern here.  Are you using Ethanol enhanced fuel?  Have you added fuel additives?  How old was the fuel at the time of storage?  How long do you in tend to store it?  How large is the tank?  Is the tank aluminum or fiberglass?  What is the ambient temperature?  Are you storing it in a closed somewhat heated building or is it in a open shed or outside?

Also there is the situation where Ethanol has been known to soften up then deteriorate the actual fiberglass tanks.  It can also clean the inside (because the alcohol softens any existing gum) of the any type of tank, allowing debris to then be sucked into the motor, causing carburetor problems.

One experienced marine mechanic related in formation garnered from a major outboard motor corporation technical training schools, where they were told that the shelf life of fuel is longer in large volumes than in small containers.  They were informed that a 6 gallon can, of untreated fuel looses an average of 4 octane every 30 days.  At this rate in 6 weeks, that fuel would be unsafe to use in a modern marine engine.  It also seems that the higher grades of gas looses it's octane rating faster than regular gas.  But most good fuel stabilizers will double the shelf life of gasoline.

If you happen to be in a location where you can not get on-ethanol fuel,  remember that alcohol attracts moisture and boats in order be used, that dictates they be near water.  The fuel tanks need to be vented, therefore, the fuel itself pulls moisture out of the air, blending it with the fuel in the tank.  After the gas absorbs as much water as it can, the water being heavier than gas settles to the bottom of the tank.  Above this water, we have the alcohol holding all the water it can.  This is called phase separation.  This can be identified by a cloudy appearance.  It is therefore possible to have water on the bottom, faze separation above that with the good gas on top.

Your fuel pickup line will be near the bottom, so you will be sucking in the worst fuel first.  This brings us to the need for a GOOD fuel/water separator in the fuel line between the tank and motor.  There are canister types using filters like a screw on oil filter that are a metal canister.  In use, you never know if they have done their job unless you remove then dump them.  Another better type uses the same type canister but has a clear plastic type bottom with a drain valve.  These can be readily observed visually.

Times have changed as for whether to keep your fuel tank full or empty.  For safety sake now days, some say keeping it empty may have way more benefits (depending on your fuel).  Read on and decide for yourself depending on your individual situation.

Some examples could be (1) with a tank of upwards to 50 gallon, full of FRESH fuel, stabilized, stored inside a building for more than 4 months, should be OK.  (2) same boat with 10 gallons, stabilized stored for 6 months, but topped off in the spring with higher octane fuel to boost the older fuel should also be OK.  (3) same boat but with 4 month old gas, with 25 gallons, no stabilization, stored for 8 months, NOT GOOD, drain or pump out & use it elsewhere. 

Now lets look at the same boat stored outside, #1 would probably be the same, however  #2 would need attention.  It would be recommended in this situation that after the first run in the spring after the old fuel has a chance to be sloshed around, with the potential of any contaminated fuel to be sucked into the fuel/water separator, to change out the separator, possibly more than once while closely watching it's contents when dumping it to eliminate the chance of contaminated water entering the motor.  Then top off the fuel tank with new fuel.

Personally I have a boat powered by a Evinrude E-Tec (a very sophisticated computer controlled) outboard motor that has a 35 gallon fuel tank.  It is stored it in unheated shed.  I try to maintain it close to full of non Ethanol fuel at all times, but do use a fuel stabilizer.  I use this boat very little if at all from early November to late March and have not seen any detrimental effects of this storage.  I have a  fuel/water separator that has the clear drainable bottom so I can check for any separation or water, but to date have never detected any.

With this in mind, for the newer higher demand marine engines, there is a potential detrimental situation that you have just created for your motor if you don't take the right precautions.  Plus, since there is no easy method to test this old fuel, you are dealing with an unknown.

You have to also remember that most newer motors are very sophisticated, many being fuel injected and computer controlled ignition/fuel consumption.   If the fuel is not compatible with the computer's injection it will not be as efficient as may be needed, which could lead to eventual motor failure.  Marine motors are subject to harsh treatment in comparison to a automobile.  A marine engine is subject to about the same as putting your vehicle motor in low gear & driving 60 miles per hour for say 2 hours or more at a time.  Very hard on the motor.  Therefore your selection of fuel and oil can be critical to the motor's longevity which could be the cheapest thing you can do to protect your investment.

Fuel Additives :   There are many companies making fuel additives that are used or designed to be on boat engines.  Some have great claims.  Some simply are a fuel stabilizer, while others do many things, like stabilizing, loosening gunk cleaning the fuel tank and engine, emulsifying the water and gasoline, even neutralize the 2 stoke unburned oil to keep your motor/ transom clean.  A few are listed below.

( STA-BIL)  Fuel Stabilizer eliminates the need to drain fuel during storage, and keeps fuel fresh for up to 12 months or more. STA-BIL now includes more corrosion protection than ever before to help prevent and protect against problems caused by today’s Ethanol-blended fuels. 

For Marine Formula STA-BIL Ethanol Treatment and Performance Improver contains DOUBLE the corrosion preventers and more than FOUR TIMES the fuel system cleaner than in Regular STA-BIL to prevent against corrosion and deposit build up in Marine Engines. Use AT EVERY FILL UP to protect your boat or other marine equipment from the damaging effects of Ethanol in the marine environment

1 oz.  for every 2 ½ gallons of gasoline, gasoline/oil mixtures, or ethanol blends.

(SeaFoam) This is a nationally known product sold thru both automotive and marine dealers.  On the can it says  - A 100% pure petroleum product for use in a; gasoline and diesel type engines. both 2 and 4 cycle.  Also oxygen sensor safe.  Cleans dirty engine parts internally by removing harmful gums, varnish and carbon.  Works and performs instantly.  Removes moisture from oils in crankcases and fuel tanks.  Stabilizes and conditions fuels.  Use for engine storage. Cures hesitations, stalls, pings and rough idle due to carbon build up.  Helps pass emissions tests.  EPA registered. Can be used for fogging for winter storage.   Tested to 60 degrees below zero.  Made since 1942

16 oz. treats 50 gallons of gasoline fuel, or 25 gallons (2 oz per gallon) of gas / oil premix.

(Startron)   This additive is sold by West Marine. A 16 oz. bottle normally sells for $21.99, however you may find it on sale for $16.49.  Their catalog says -- New enzyme-based additive increases fuel economy and engine power while reducing emissions.   Stabilizes gas for short and long term periods of inactivity (up to one year) while preventing the formation of varnish.   Eliminates carbon buildup in fuel delivery system and exhaust components.   Increases octane and removes water from the fuel, making it the perfect solution to prevent and eliminate ethanol (E-10) fuel problems.  Fights organic growth without biocide!  Reduces fuel consumption and engine wear while increasing power.  Enzymes treat water in fuel.   For use with any engine; not toxic to the environment.

16 oz. treats 256 gallons of gasoline.

(Soltron)   Retail price is normally at about $20 for a 16 oz. bottle.  This is called an enzyme fuel treatment and uses 100% natural enzyme technology to deliver multiple benefits to all gasoline and diesel engines.  Effects can be felt in as little as 30 minutes.  Don't worry about using too much as it is pure fuel and harmless to any engine.  It is a powerful dispersant which may loosen and dislodge heavy accumulations of sludge, including deposits caused by overuse of other fuel additives.  Fuel filters may require servicing when first using SOLTRON in contaminated fuel.  Removes bacteria and mold, cleans injectors, will rejuvenate ethanol water separated fuel.

Many boaters of 2 cycle motors report that this product eliminates the black carbony stains on the stern and motor parts at water level,

16 oz. treats 500 gallons of fuel or 1 oz per 30 gallons.  This amounts to about 3/16 oz per 5 gallons.  The old bottle is marked in 1 oz. divisions. 

A salesman for Soltron says that Startron is the same product as Soltron, except in a weaker (near 50%) concentration.

(Yamalube Fuel Stabilizer & Conditioner PLUS)   Strongly recommended for E-10 fuels, this alcohol-free formula helps prevent fuel oxidation and phase separation from moist, rich air. When used continuously, it keeps fuel fresh, potent and free from gum and varnish for up to one year of storage. Its metal filmers, provide extensive protection for steel and aluminum components.

Alcohol-free Yamalube Fuel Stabilizer and Conditioner PLUS is specially formulated to help protect your engine's fuel system from the harmful effects of ethanol-enriched fuel, including its corrosive effects on metals as well as fuel system gum and varnish that can result from fuel oxidation. Also effective with non-ethanol fuels. When used as directed, helps keep fuel fresh and potent during normal use.

For maximum fuel system protection, use this product on a continuous basis.   Add 3.2 oz. bottle of Yamalube Fuel Stabilizer & Conditioner PLUS to every 5 gallons of fresh gasoline.  For off-season storage ask your Yamaha dealer for the concentrated version in 12 oz. and 1 quart bottles.

When you add these additives to your fuel, do not skimp when you guess how much is needed.  This may be the cheapest form of insurance you can buy.


copyright © 2011 - 2015  LeeRoy Wisner  All Rights Reserved

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Originally stated 02-04-2011, Last Updated 12-14-2014 
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