Best Way To Clean Years Of Sludge From Fuel Tank?

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  • John Gragg

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 128
    Topics: 36

    Thank you to those who answered my call for help on the TD20 slow speed issue previously posted. I followed the details in the Red Book regarding the carburetor adjustments and possible issues (pgs 87 – ?).

    So it very possibly comes down to a very basic issue. My fuel tank, although I thought I had it cleaned out very well, is still putting out sediment. This is an EBAY cast tank that came to me very caked in varnish and sludge. The petcock would not allow even a drop of fuel (I was cleaning with alcohol) out. When I removed the petcock it was caked full of dried dirt/dust/sediment.

    Anyway – I spent the better part of a couple of days soaking in alcohol, agitating by hand, scrubbing the inside with #6 birdshot from about 8 shotgun shells, etc. I thought I had it pretty well cleaned out, enough so that I put the fresh fuel in it for my test runs.

    Well, after the lean condition and suggestions that I had a fuel delivery issue I went straight to the tank. Drained about 1/2 cup of fuel into a clean, clear glass jar and let it sit. The sediment is clearly accumulating on the bottom.

    Pulled the carb, yep! Sediment already collecting on the check-valve screen and other parts of the carb.

    So – My question. What is the best way to get this tank clean, for good? I don’t have it in me to shake a 3/4 full gas tank for hours on end, so I need something that will get me truly clean.

    Since this is a cast tank, it has a seam where the two halves are screwed together. Is taking it apart for cleaning an option? If so, does it require a gasket? What sealer would I use to reseal, if it is even possible?

    The permanent tank I plan to use is already painted so I can’t use it right now. And I would like to have this tank available to use on future projects if possible.

    Any advice?

    Lastly…Would this amount of sediment cause my troubles? I’m thinking the answer is a BIG YES, YES, YES, but I’d like to know your thoughts?


    John Gragg
    RIverside, CA

    Just starting in the hobby, please be patient.

    49 Sea King 5hp GG9014A
    49 Johnson TD20
    48 Johnson TD20
    54 Johnson QD15
    55 Johnson CD12


    US Member - 1 Year (includes $3 online payment fee)
    Replies: 1063
    Topics: 107

    I use the solvent of choice along with a length of chain.  Tie a wire to the chain so it doesn’t get “lost” in the tank.  Then SHAKE SHAKE SHAKE.  or, if you get tired of shaking do what this guy did…..

    Some people use nuts and bolts instead of the chain but they can be challenging to remove.

    In the meantime I would place a fuel filter in the line from the tank to the carb.


    US Member - 1 Year (includes $3 online payment fee)
    Replies: 2405
    Topics: 56

    I’ve used denatured alcohol along with a handful of hex nuts, then shake until you can’t shake anymore.  As seakaye noted, a length of small chain might be better as getting the last few hex nuts out can sometimes be difficult.


    1937 Champion D2C Deluxe Lite Twin
    1954 Johnson CD-11
    1957 Evinrude Fastwin 18
    1958 Johnson QD-19
    1958 Johnson FD-12
    1959 Johnson QD-20

    “Every 20 minute job is only a broken bolt away from a 3-day project.”
    "Every time you remove a broken or seized bolt an angel gets his wings."


    US Member - 1 Year (includes $3 online payment fee)
    Replies: 7290
    Topics: 1053

    I usually use a bunch of wood screws to shake around…… lots
    of sharp edges. The ones I can’t shake out get plucked out
    with my telescopic magnet.

    Prepare to be boarded!

    Steve A W

    US Member - 2 Years
    Replies: 751
    Topics: 51

    I’ve had success with E85 fuel and shaking.
    Something I’ve thought about is using rotisserie
    from a grill.
    If it will rotate a turkey it should handle an aluminum
    gas tank.
    Good luck with it.

    Member of the MOB chapter.
    I live in Northwest Indiana


    US Member - 1 Year (includes $3 online payment fee)
    Replies: 606
    Topics: 41

    After trying out many different cleaners for aluminum tanks, probably the most effective for removing old fuel mix deposits was ammonia. Best to remove the filter screen and replace it with a 1/2″ brass plug from a plumbing supply prior to shaking. Otherwise, the hardware that you are using for the mechanical removal will damage the intake filter screen.

    Time and patience are the key here. You can shake the tank, then set it down on a different side each time for even treatment. This can take days instead of hours and may require a couple of rounds. I do recall a member that set up a drill with a drum sander to rotate a bicycle wheel with the tank attached.

    No matter how well the tank is cleaned, expect more stuff to come out after it’s put into service. After fuel mix sits in it for months, the last of the most stubborn crud will come out.

    Regarding the two-piece cast tank, I wouldn’t take it apart unless it is leaking, or you want to restore it. There is no gasket between the halves. Permatex anaerobic sealant is one product that will work for the reseal and is available widely. A thin coat is all that’s needed. Of course, preparation is the key with good clean mating surfaces.


    US Member - 2 Years
    Replies: 145
    Topics: 40

    aquasonic is correct in using ammonia for old gas deposits.   And patience–it has taken me a week or more to clean all the residue from some tanks.  The used ammonia can be filtered and used again.  Buccaneer is correct in using wood screws, there is nothing better.


    US Member - 2 Years
    Replies: 576
    Topics: 42

    Disclaimer; Each of us have our oun methods whic may or may not suit various situations. Results may vary from desired.

    I had an early postwar Scott single with a cast tank and side covers. Tank was about a third full of solid remains of fuel  Removed tank, plugged fuel outlet, poured in ladquer thinner, replaced cap and set out in sun. After a week, poured out a jelly like substance and excess lacquer thinner. Poured the lacquer thinner back in tank. Repeated several times until tank yielded no more jelly.

    A member of GLC converted an old wringer washing machine to slowly turn a tank so nuts  and cleaning solution could work on deposits without manual effort.

    I have split and resealed a number of Mercury 2 piece cast aluminum tanks. Practice may not make perfect, but, it will improve your technique. It is    I ASSUMME that other brands may also be split and resealed.

    If carb and tak have had issues, it is possible fuel filer, shutoff and fuel line may need attention.





    International Member - 2 Years
    Replies: 76
    Topics: 9

    I prefer the short length of chain.  Only one thing to get back out of the tank, as opposed to dozens of screws/nuts/bolts


    John Gragg

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 128
    Topics: 36

    Resoaked over night with alcohol.

    Drained and rinsed alcohol out, used sidewalk nozzle to rinse out tank especially the gunk in the rear of the tank. It was 3/4″ thick!

    Used 1/2 cup muratic acid with 95% remainder of tank of water. Shook like heck, let it sit 30 minutes. Fortunately I opened the vent right after shaking because the mixture was a little excessive on the acid side I guess. No damage, no foul, just a little bubbly.

    Drain, rinse, repeat.

    Neutralized with two baking soda baths, then lots of rinsing.

    Great results!

    Clean as a whistle. I’m going to use Por-15 tank sealer on it after it dries really well. I might even use my heat gun just for good measure.

    Thanks for all the advice. I might Crack the tank open some day and do a complete restore on it, bit for now it’s just for testing.

    Best Regards

    John Gragg
    RIverside, CA

    Just starting in the hobby, please be patient.

    49 Sea King 5hp GG9014A
    49 Johnson TD20
    48 Johnson TD20
    54 Johnson QD15
    55 Johnson CD12

Viewing 10 posts - 1 through 10 (of 21 total)
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