Gasoline shelf life?

Discussion in 'All Things Boats & Boating' started by gerard baladi, Nov 23, 2008.

  1. gerard baladi
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    gerard baladi Junior Member

    I have a boat that has been sitting high and dry for about a year or so, Fuel tank full (200 liters+-)

    How do I know (or test) if the gasoline is still good?
    Would adding fuel enhancers improve the gasoline to be used again?
    In case the Gasoline is beyond usage, How do I dispose of it?

    Any suggestions will be greatly appreciated.

  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Your gasoline was several million years old when you bought it, so a year more or less won't make much difference. It may have dissolved (weakened) rubber parts like flexible fuel lines and seals, but maybe you have none.
    What can happen is, that some very light fractions have combined to form longer chains (polymerize), causing some chemical changes like another smell, but they will all still burn.
    I have a classic car in my garage that I start once a year, drive it to the next village and back, clean the garage floor and put the car back in.
    The tank was filled in 1994...
  3. clmanges
    Joined: Jul 2008
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    clmanges Senior Member

    I saw somewhere that gasoline starts going bad after a month or so -- what a bunch of hogwash. I heard that it will form something like shellac if it sits too long, but I don't know if there's anything to that, either. May be one of those things that was true many years ago, but no longer, due to some additive.

    If you're worried about it, you can go to an auto parts store and buy a can of fuel stabilizer for a few bucks, but you probably don't need to.
  4. gerard baladi
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    gerard baladi Junior Member

    Thanks Guys, It's a relief.
    I starting getting worried when I got that same info that it goes bad.
    I also have a 1979 El Camino, but I do enjoy driving it around. (although it swallows gasoline)
  5. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Sorry guys, but Diesel and Gass both go bad (or at least all of it manufactured since 1910 or so). There are a number of different reasons for it, and I am not a fuel engineer, but I can at least point you to some places that may add some science to my answer.

    First you need to understand that petrolium fuels are not made up of one type of molocule. There are tens or hundreds of different chemical compounds found in every gallon of fuel, and not all of these have the same properties. This is in addition to all of the chemical additives mixed with the distilled fuel for reasons ranging from lubrication enhancers, fuel stabalizers, chemical catalysts added during the refining process, thermal property modifications, vaporization control compounds, ect... Each of these compounds can effect the long term storrage of the fuel in different ways, but when combined they must be dealt with a a whole.

    Now that we understand what we are talking about, we need to understand a little bit about how fuel is refined. A century ago crude oil was heated to different tempratures and those compounds that were volitile at that temprature gassed out from the crude and were labeled based upon that. Modern refining takes this a step further.

    Once the volitiles are seperated by heating the larger, heavier compounds are broken into smaller ones (say from tar to gassoline) by the addition of chemical catalysts. This increases the yield of high priced fuels (gas/diesel) from one barrel of crude at the same time reducing the amount of low cost by-products (tar/asphalt).

    The next step is the removal of other compounds that for one reason or another are no longer desirable in modern fuels (Sulpher from diesel for instance).

    The end product then is a heavily engineered fuel designed to be put into regular gass engines. Like many on this forum know there are ALWAYS trade offs when designing anythine, and the fuel companys have made a decision to design fuels for vehicles that routinely need to be filled up. In other words vehicles that do not store significant amounts of fuel for any period of time.

    So what happens over time:

    1) The highly volitile chemicals in the fuel start to evaporate away and leave the heavier compounds behind. To some degree this can be controlled by vapor proof containers, but even the best in time will allow some percentage of vapor to leave.

    2) The chemical catalysts used to break the large chains start to degrade and the bromen chains reform back into heavier compounds.

    3) Oxidation occures further accellerating the breakdown of large strand organic compounds. Similar to the reason why doctors now say we should drink red wine regularly (for the anti-oxidants)

    4) To some extent there are algie capable of living in the surface barrier of water and fuel. As these colonies die their remains form yet another trapped solid that can clog fuel lines, filters, and generally mess stuff up.

    So what does this mean to us?

    The major manufacturers of fuel, I looked at chevron and exxon, indicate that diesel has a shelf life of between 6 months and 1 year, with gassoline having a shelf life of 3-6 months. The filter manufacturers say that this time is really 1-3 months from refining for gass and 3-6 for diesel. With the fuel system managing companies varrying between these numbers. But I think it is safe to assume the real numbers can't be longer than 1 year for diesel and 6 months for gass.

    Some websites for further reading
    2 people like this.
  6. Ike
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    Ike Senior Member

    Interesting info. On top of that, letting fuel stand in the fuel system for long periods of time degrades fuel hoses, gaskets, and other plastic parts. I have a 1980 2hp johnson. I always run the fuel out of the system, and if going to let it sit for months, I empty the fuel tank. It runs perfectly and has never had anything other than routine maintenance. I once did not use it for over two years, and after checking and cleaning the spark plug and filling the tank, it started on the third pull. So if you are going to let the engine sit for 3 months or more, run the fuel out of the system (simply shut off the fuel and run the engine until it quits). If you don't want to drain the tank, add a stabilizer to prevent phase separation, and you can add stuff to keep the bugs from growing as well.
  7. marshmat
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    marshmat Senior Member

    Some nice research there, Stumble.

    Some engines are more tolerant of crappy fuel than others. My Johnson 30 will reportedly handle 67-octane, and I know a guy who once ran his Chevy pickup on Coleman camp fuel when he ran out of gas. On the other hand, a modern fuel-injected engine or a smaller outboard with its tiny jets may not respond so well.

    The main issue with old fuel seems to be the solids or gel-like substances that come out of it when it's been sitting for a while. This "fuel varnish" is a real pain to clean up, and so for my engine, I'll add stabilizer to the last tank of the season and, at haul-out, run the carb dry while on the flush fitting.

    If you don't have any solids or contamination in the bottom of your tank, Gerard, the fuel that's in there could very well be OK. You might have to change the fuel filter a bit early, though.
  8. El Sea
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    El Sea Junior Member

    Here in the US of A we have ethanol being introduced in to all vehicles. I clean fuel tanks and todays fuel are turning bad at a higher rate than before. They not only turn bad, they are attacking the rubber components within our fuel systems. Vehicles older that 5-8 years old are see a higher degree of problem. The newer vehicles are weathering the change better.

    Here in Florida the state had a posting applied to all gas pumps ablout the size of a business card stating the fuel contained up to 3% ethanol. Now the state has applied a placard large enough to be read twenty feet away stating the contents can be up to 10% ethanol. The change in the size of notice is actually a warning to all consumers.

    Gas is being phased over to a higher ethanol blend while the diesel is being reduced in sulfur and more blends of bio are showing up. The diesel tanks we clean are as problematic as the gas tanks. From the gas tanks we are removing what I call 'oatmeal' and from the diesels tanks it can be a thick glob or a black mealy product. All of which depeand on how the owner took care of their fuel.

    Good Luck to All,

    El Sea
    'What's in your tank?"
  9. Guest625101138

    Guest625101138 Previous Member

    Clearly you have the illusion of driving the car each year. It cannot possibly work with 14 year old fuel!!!!!

    I accept there are relatively slowwww chemical changes in a sealed container but slow is the operative word in terms of our time frames here.

    With two strokes using oil/fuel mix I have seen carburetor parts gum up with oil residue after evaporation has occurred. This can happen inside a few months.

    If the fuel tank is breathing then the light fractions will be lost to atmosphere and ignition could be difficult to impossible for a spark ignition engine. A lesson I learnt about storing lawn mower fuel. Will deteriorate to the point of hard starting inside 6 months if the tank breaths and it is being temperature cycled from teens to high twenties in centigrade. Typical Australian summer.

    I expect only highly tuned engines would notice any loss in performance using fuel that had been stored in a sealed container for 6 months. Certainly not at a stage to be discarded.

    One other thing I have seen is fuel reacting with a "protective" surface film placed inside a fuel tank that peeled off and turned into rubbery flakes. Gives the illusion of scum formed from the fuel when removed from the filter.

    Rick W
  10. gerard baladi
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    gerard baladi Junior Member

    I will try and empty the tank (since I am hardly using this boat), Is there a way to test the gas (other than putting it a car or boat and get stranded).

    Would adding Fuel enhancers do the trick?

    Thanks guys for keeping this thread alive
  11. Guest625101138

    Guest625101138 Previous Member

    If you blend it into your car fuel tank over a few fill ups it should not make much difference.

    If you have a small IC engine like a lawn mower or grass trimmer you could try a few tanks through one of those. If they are hard to start then you could have the same problem with a car or boat.

    Most important aspect with storage is to ensure it is properly sealed so the volatile components are not lost. This is likely to be the biggest issue right now. It will still burn well but could be more difficult to ignite.

    Rick W
  12. Stumble
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    Stumble Senior Member


    you can send fuel off to a lab for testing, but this is probably more expensive than it is worth for what you are doing. Fuel additives can be any mix of stuff, and like I said this is not my area of expertise, but I doubt most of them are worth adding. Some of the diesel fuel stabalizers might be, but I don't have any science I trust saying that they are. Plus if any are worth it why arn't the big oil companies adding it themselves?

    As for how to handle it, I guess it depends on exacally how old the fuel is. If it is 6 months old I would top off the tanks with fresh fuel and run it, but bring extra filters. If it is a few years old I would probably just dispose of it depending on the amount.

    I know for diesel there are fuel polishers that work pretty well to cycle out junk but I don't know if they work on gass.
  13. Guest625101138

    Guest625101138 Previous Member

    One more point. If the existing tank is not well sealed you might be getting condensation in it as well. This settles to the bottom so be careful when you draw off that it is not contaminated with water.

    Rick W.
  14. Frosty

    Frosty Previous Member

    Why don't you try a bit in the car. 200 liters is a lot to throw away and I would not. You would be able to shift that very quickly in the boat anyway. What about adding some fresh to the point that its Ok, providing that the car doesnt like it.
    I have had probs with petrol going off but thats after years and I doubt if your big jetted American iron engine will struggle with it.

    As far as diesel!!! I have on the dock 80 liters I bought a year ago and I still consider that to be fresh. I have over a ton in the tank that is 4 years old.

    My engines are new 4200RPM double stage injected Yanmars.

    Diesel may discolour but still runs the motor. Now if you are saying the fuel has lost .05 % of its calorific value at 30 degree I will not disagree, but it runs the motor in a satisfactory way that you will not notice.

    Again if you say that a cold engine in winter will emit 10%more smoke on cold start with 3 year old diesel I wont disagree, but you don't throw it away.

    Im sorry that this does not fall in with various web sites but in my old age I knows what I knows.

  15. CDK
    Joined: Aug 2007
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    CDK retired engineer


    The car is a Porsche 928S from 1980. I do not need it here on the island because the roads aren't good enough and I need 4 people to get it on the ferry. The current value is too low to sell it, so it waits for better times in my garage.
    It needs some air in the tires and a battery to come to life; it has always started at the first attempt, the last time being just 3 weeks ago. After 14 years the tank is still half full.

    There are so many fairy tales kept alive by interested parties. I've even seen building bricks with a printed text "use before .....".
    The 'cracking' of oil to obtain more fuels is done with catalysts as "Stumble" wrote, but it happens at very high temperatures and pressure. The process reverses during long storage, long being expressed in centuries, not in months. There is also oxidation and evaporation, but the surface is very small when compared to that of the vaporized fuel inhaled by the engine.

    For 2 stroke engines the story is completely different. They start very reluctantly or not at all after a year's storage because the fuel in the carb has gone, leaving only a few drops of oil that clog the metering holes and nozzles.
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