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Is my diesel fuel rotten?

  • August 21, 2011 5:16 AM
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    Message # 681310
    Anonymous
    I decided to pour the 6 month old diesel from my 5 gallon jug into my tank, but when pouring I noticed a "rotten" or "sour" smell. I know that nasties can grow in diesel and I assume this is the cause of the odor, but how can one tell when it's too far gone? I did not add bio-diesel additive because I figured I would use it up before any substantial growth could occur. Was I wrong? Will rotten fuel hurt my engine? 
    Last modified: August 21, 2011 5:17 AM | Anonymous
  • August 21, 2011 10:01 AM
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    Reply # 681441 on 681310
    Anonymous
    If the fuel is suspect, hire a qualified pro to come clean your fuel or "polish" it for you.  They can usually clean out your tank at the same time.  If that is impossible.... 

    Filters are what should protect your motor from things in diesel that your motor will be damaged by.  Namely that is water or debris (organic or otherwise).  If there is biological matter in your fuel it will quickly accumulate in a filter, clogging the filter, then the motor will die due to fuel starvation.  Of course the "fix" is to clean up the fuel and then change the filter, then bleed the system. 

    Most boats have at least 2 fuel filters.  One filter will be mounted on the engine itself.  Generally it will be immediately in line after the hand priming pump and before the injector pump.  It should be a spin on type filter. 

    Trace the supply side of your fuel line back to the tank.  There will usually be another filter between the motor and the tank.  That is the filter you should be most concerned with.  It will clog first.  If you do not have a filter there, you should consider installing one to protect your motor. 

    Organisms grow in the fuel because water is introduced into the fuel.  If this is a problem often for you, investigate ways water could be entering your fuel.  Was your jerry jug left outside for a long time?  Are the seals tight?  Did it expand and contract many times in the sun? 

    If you add something to the fuel to kill the infestation, it will result in a lot of organic matter dying and drifting to the bottom of the tank.  This will speed up the process of clogging, so be prepared.  Ie, don't go out on a big sail with suspect fuel. (carry spare fuel filters!) Most additives combat the problem by removing water from the fuel.  Some are actual biocides that kill what is growing.  If you decide to use it, do not over use it.  And add it on a regular basis.  Think of it as a preventative medicine rather than a "quick fix". 

    Hope this helps. 

    Tate
  • August 21, 2011 11:40 AM
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    Reply # 681478 on 681310
    Anonymous
    Thanks, nice surprise getting such a clear and comprehensive answer. I didn't know that water ingress was the culprit behind contaminated fuel. 

     I have a small fuel tank, so having someone come to the boat to polish the fuel, would cost way more than the actual value of the fuel. Currently, have about half a tank full. The quote from the mobile fuel polishing dude in Colonial Beach VA was $300.000. 

    I was hoping to discover a way to measure the "goodness" of the fuel.  Is there a test kit I can purchase that will measure the amount of biological material in the fuel?

    Worse case, I guess I could just siphon the fuel into jerry jugs and throw it away. In an environmentally responsible way of course :-)

    Eric
  • August 21, 2011 11:50 AM
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    Reply # 681489 on 681310
    Anonymous
    Eric, 

    You may want to try to "polish" it yourself.  Siphon it out of your tank into jerry jugs.  Purchase one of those "baja" type fuel filter funnels and pour it through that back into your tank along with some additive to keep the water/bio down.  This will take some effort as those funnels are not fast.  I have no affiliation with Jamestown, its just the first link I came across to show you what I'm talking about: 

    Hope this helps. 

    Tate


  • August 21, 2011 12:00 PM
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    Reply # 681498 on 681310
    Anonymous
    Not sure on test kits.  I've never tried to test the fuel.  Usually if you have biological contamination you'd find some gooey junk in the fuel itself.  Look for it. You'll know it if you see it.  Just pour it through a fine mesh.  If you don't find any, you might be okay.  I've never "smelled" contamination beforehand so I have no idea.  Smelling rotten could just be some sulfur smell. 

    As another side note for the curious...  Water is not the "actual" cause, its just the controllable part of the cause of diesel bio contamination.  Diesel is a great food source for micro organisms.  It provides carbon that a lot of organisms like to eat.  It also provides sulfur and oxygen for their respiration.  We can't fix that.  Water is needed for many of these baddies to reproduce though.  So if fuel is contaminated and water gets into it, they will begin to grow.  Keeping water out the tank will keep them from getting started. Most diesel additives to control growth just remove water from the fuel.

    Water can get into the tanks from poor seals like your o-ring on your fuel fill.  It can also enter if there is a lot of temperature change that causes your tank to vent out air and pull more air in.  Some people recommend keeping a full tank for this reason, to reduce the amount of air circulation.  Though its somewhat questionable how much water can actually condense in a tank this way.   
  • August 21, 2011 12:03 PM
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    Reply # 681499 on 681489
    Anonymous
    Tate McDaniel wrote:Eric, 

    You may want to try to "polish" it yourself.  Siphon it out of your tank into jerry jugs.  Purchase one of those "baja" type fuel filter funnels and pour it through that back into your tank along with some additive to keep the water/bio down.  This will take some effort as those funnels are not fast.  I have no affiliation with Jamestown, its just the first link I came across to show you what I'm talking about: 

    Hope this helps. 

    Tate


    Thanks Tate, I might be going that route, that filter looks like a pretty inexpensive way to handle it.

     I sure wish I had a way to test the fuel. After all, the fuel may be good enough to use without polishing. I'd hate to go to all that fuss and muss if the fuel didn't need polishing.
  • August 21, 2011 12:08 PM
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    Reply # 681502 on 681310
    Anonymous
    Maybe its fine.  If you want to just let it be, just make sure you familiarize yourself with how to change your fuel filters and how to bleed your engine's fuel system.  If it clogs up, you may have to do it underway.  

    In any event, its prudent to have those skills.  You can also check your filter now, then run the motor for a while and check it again to see if it has any debris clogging it up progressively, etc.  
  • August 21, 2011 12:19 PM
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    Reply # 681506 on 681310
    Anonymous
    As a teenager, I had a job fueling small aircraft at Manassas airport. One of my tasks was to remove water from the fuel tank by way of a bleeder valve underneath. I wonder if installing something like that on my tank would be a good thing?
  • August 21, 2011 12:24 PM
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    Reply # 681508 on 681310
    Anonymous
    Eric, 

    Almost all diesel fuel filters separate water from the fuel as it passes through them.  There is a drain in the bottom of them to remove the water.  The problem is though that the fuel/water isn't separated until it passes through the filters.  That means that water sitting in the tank allows growth.  

    Some people build a "polishing" system into their boat with a pump that will cycle the fuel in the tanks through the filters without the engine running.  Bud has a diagram of this type of setup that you may want to ask him for.  Though if you're on a tight budget that might be overkill at the moment. 

    Tate
  • August 21, 2011 4:25 PM
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    Reply # 681601 on 681310
    Anonymous
    On a budget? HAH! That's an understatement, I just did a rough draft cost assessment of all the major projects I either need, or want to do. I stopped at 26K because it was so depressing. This refit is gonna take a long time, i think.

     But seriously, I wouldn't have it any other way. Learning about, and tinkering with this boat has been the most interesting project that I've ever been involved with. The boat can have all of my discretionary income for all I care.