Fuel Tanks and ethanol....

Discussion in 'Metal Boat Building' started by Accurate twrs, Mar 16, 2010.

  1. Accurate twrs
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    Accurate twrs Junior Member

    I"ve been giving some thought to the ethanol problem in fuel tanks... Seems if you could separate out the water from your gas you may have a better chance at improved performance and hopefully not damage you boats motor.

    By fabricating a separator box in the bottom of a fuel tank you can drain out the water from the gas and reduce water from ever running through your fuel system.

    Does this sound doable... Your thoughts and ideas...!!!
     
  2. rasorinc
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    rasorinc Senior Member

    We always had tank drains on single engine aircraft at the lowest point. Good idea if you have the room. The drain tank has to sit lower then the main tank but only has to hold a gallon maybe but it is a manual operation. Real easy when the tanks are in the wings.
     
  3. marshmat
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    marshmat Senior Member

    A sump drain of some kind would seem to be a prudent precaution in tanks of all sorts. It would help with all sorts of crud that builds up in there.

    "Southeast" - as in southeast USA? Something like half of all ethanol complaints seem to come from there. I'd be really curious to see a chemical analysis of your gasoline- our 87 octane here in Ontario is up to 10% ethanol, and many folks leave it sitting around in the tank for eight months of winter with no ill effects come springtime. Something about the additive packages, perhaps?
     
  4. TollyWally
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    TollyWally Senior Member

    I'm as far from Southeast as you can be in the continental US and they put some damn thing in there around my neighborhood. Additive packages or Satan's octane booster, what ever the stuff is it raises pure hell with older tanks. I ended up rigging together a homemade fuel polishing set up and ran my fuel from tank to tank for a day. Now I run my fuel through a double set of Racor diesel filters before it runs the gauntlet of stock filters. So far it's been working but I've only really ran a couple hundred gallons through the motor. So far so good but it's cost me hundreds of dollars in filters and carb repair. The gov't. is so smart, buy off the corn belt vote and poison my boat. Idiots!

    I was under the impression the Coasties frowned on drainable gasoline sumps. I may have to have a new tank fabricated, a sump would be a good thing.
     
  5. marshmat
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    marshmat Senior Member

    They frown on drains coming out the bottom, but I'm not aware of anything against a sump with a pump-out. In other words: have a small sump built into the tank, with a pickup line running to the bottom of the sump, and some way (a cheap hand pump, perhaps) to suck the crud out this line. Then have the real fuel pickup mounted a few inches higher.
     
  6. TollyWally
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    TollyWally Senior Member

    That sounds like it woud work real well Matt. I know how I'd prefer to do it but your way is safer and will keep me from all sorts of trouble with all the various powers that be.
     
  7. gonzo
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    gonzo Senior Member

    Gasohol has a short shelf life. It starts separating in about a month to six weeks. Ethanol alone is corrosive (because of the water content, it's hygroscopic) and also disolves hoses, gaskets and seals when it is in a high concentration. Henry Ford first started using ethanol on fuel in the Ford Gas he sold at his fuel stations. When lead became available, it was better and cheaper so they all switched to that. All tanks have a sump; the pickup tube is at a distance from the bottom.
     
  8. CDK
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    CDK retired engineer

    Let's not mix facts and fiction.

    Jack Daniels nr 7 used to be 43% ethanol, Wild Turkey even 54%. I've never heard of glass corrosion and even the 1 cent cap and seal are never affected by ethanol.

    Yes it is a solvent, but a poor one compared to nearly all other hydrocarbons in gasoline. If fact the only distinction (besides taste and smell) between alcohol and the other HC's is its ability to mix with water.
    Some fuel system manufacturers have used cheap materials in the past because they assumed there would be no water present, but they all use neoprene seals, brass fittings and PVF fuel lines for more than a decade.

    The hygroscopic property of alcohol must not be exaggerated and can also be regarded as an advantage because it avoids engine starting problems from water filled carbs.
    If you feel really unhappy about the invisible presence of water in fuel, unscrew the now useless water separator from under the fuel filter and fill that with silica-gel pellets.
    Keeping the tanks topped up after a trip also helps to reduce moisture contaminating your fuel.
     
  9. gonzo
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    gonzo Senior Member

    With glass engines I would say you are right. With aluminum for example, ethanol produces a lot of corrosion. Pure etanol will destroy a carburetor. I worked in Brazil where 100% ethanol or 90% is the common fuel, and older engines had to get new carburetors with special coatings or be in cast iron. Aluminum tanks have problems too. Most fuel lines, unless they are specially formulated, specifically say not to use fuel with more than 10% ethanol. The same goes for the rest of the fuel system. I am refering to USA systems and materials, which I assume is what he has.
     
  10. Bigfoot1
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    Bigfoot1 Junior Member

    gas drain

    You can build a tank with a catch but you cannot by AYBC rules, have an open drain or valve below the top of the tank Instead make the sump and put in a draw line, into the sump with a valve and fitting on top. I think, but not sure that this valve requires a lock on it so it cannot be inadvertantly opened
     
  11. gonzo
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    gonzo Senior Member

    If you make the draw line with a threaded end and put in a cap it would be legal.
     
  12. TollyWally
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    TollyWally Senior Member

    If that is true that is the way to go.
     
  13. CDK
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    CDK retired engineer

    Can somebody please clarify with at least some credibility how alcohol interacts with aluminum?

    I am not a chemist, but technical chemistry was one of my favorite college topics: I cannot understand what sort of reaction could take place.

    Gonzo claims first hand experience with ruined carburetors, but my wife prepares Coque-au-vin or Boeuf Bourguignon and never complains the boiling wine ruins her aluminum pans.

    Could it be that these stories are kept alive for commercial reasons?
     
  14. Bigfoot1
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    Bigfoot1 Junior Member

    Re Gonzo remark about putting a threaded end and putting a cap on it.
    I would stay away from this without putting a buffer in place. Aluminum fittings on aluminum fittings will often gall the theads. The result is could be a poor seal when you put the cap on and off a few times.
    Remember on an aluminum tank you cannot cannot use brass or bronze fittings only 300 series stainless or aluminum.

    but if you want to use a cap, put in some stainless buffer into onto the draw line that will stay attached to the drawline thread, then put a stainless cap on a stainless nipple.

    When we build diesel or gas tanks in aluminum, for even regular draw lines, this is the procedure that we use. If you dont believe me, try on a bench tightening an aluminum fitting into another aluminun pipe fitting leave it a year, then undo it.
    I would say the survival rate of the the thread would be about 50%
    Additionally if you decide to use a thread sealant ONLY FOR LUBRICATION , as fuel vapor will dilute it, ensure that it is aluminum compatible. Not a copper based sealant.

    copper and aluminum are not galvanically compatible
     

  15. CDN-CUCV
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    CDN-CUCV Junior Member

    I am not a chemist either, however, I hope this can shed some light on the subject: For in the case of aluminum tanks, aluminum is a highly conductive metal that relies on an oxide layer for its corrosion protection properties. Low levels of ethanol, such as E10 (10%), are usually not a problem in aluminum tanks because the oxide layer provides a good measure of protection. The problem occurs when the ethanol content is increased.

    There are two mechanisms that occur with ethanol. Both mechanisms are a result of the hydroscopic property of ethanol which was mentioned. The more ethanol in the fuel, the more water there will be in the fuel tank. Water not only causes the tank to corrode, it also causes the corrosion particles to clog fuel filters, fuel systems, and damage engine components. The corrosion rate can be accelerated under a number of conditions if other contaminating metals are present such as copper which may be picked up from brass fittings or as a low level contaminant in the aluminum alloy. Chloride, which is a chemical found in salt water, will also accelerate corrosion. In the long term, corrosion can perforate the aluminum to produce leaks that would cause fuel to spill into the bilge and end up in the environment. In the worse case it could cause a fire and/or explosion hazard. Boat fuel tanks are often located under the deck next to the engine where the operator might not be aware of a leak until it was too late. .

    The second mechanism that can occurs with the increased use of ethanol based fuel in aluminum tanks is galvanic corrosion. Gasoline fuel is not conductive, but the presence of ethanol or ethanol and water will conduct electricity. The galvanic process that occurs to aluminum trim tabs, stern drives, shaft couplings, etc. will occur within the aluminum fuel tank. Boat builders are able to protect exterior aluminum boat equipment with sacrificial anodes known as zincs. Sacrificial anodes are not a feasible option for the interior of a fuel tank.

    I, personally, have known one welder to lose his life to an explosion resulting from hydrogen gas build-up in an aluminum fuel tank. Recently, another local shop had a fire as a result of a enclosed buoyancy tank exploding that had hydrogen gas inside from use a certain bilge cleaner which reacted with the aluminum. This happened in both cases, after extensive flushing of the tanks.
     
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