cleaning a gas tank

Discussion in 'All Things Boats & Boating' started by donaldmay1953, Jun 15, 2012.

  1. donaldmay1953
    Joined: Jun 2012
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    donaldmay1953 New Member

    I found an old thread here and got a lot of great info on cleaning a gas tank.

    I just picked up a 1996 225 Aquasport that had been sitting for 5 years. Replaced blown 225 Yamaha with a rebuilt 2001 225 Merc EFI. I pressurized the tank through the vent tube with 80 PSI and it took every bit of fuel out like a charm. I put 2.5 gallons back in with gas dry, let it sit overnight, repeated the process twice, and the fuel is as clean as it way out of the pump. Replaced filter, filled the tank, and all is good. Lots of great info on this site.

    Don't exceed 80 PSI, or your tank will start to sing to ya.

  2. philSweet
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    philSweet Senior Member

    You're a lucky man, Donald. Anyone one here know what the factory pressure test is?
    The average life of an Aluminum tank in Florida is about 14 years. I'm going to go out on a limb here and guess that the reason the boat didn't blow up is because you already have a leak in the tank that can handle more than your compressor can put out. Pull the deck off. Dig out the foam. Replace the tank and hoses. And please don't anchor next to me until you have done this:p
    Last edited: Jun 18, 2012
  3. philSweet
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    philSweet Senior Member

  4. donaldmay1953
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    donaldmay1953 New Member

    Alum tanks last about the same anywhere. Good thing mine is polyethylene. Remember, pressure testing and putting pressure in something are two different things. According to the post on this site that I got the idea from, the only way to force fuel from the tanks is to put pressure in them. With a 1/2" dia. hose for the fuel to flow from, it would be almost impossible to "blow it up" at 80 pse. By keeping a constant 80 psi, the fuel comes out quickly and evenly.

    I am not sure how they do it in Florida, but up here, most of the yards use this method quite often to clean tanks, even aluminum ones.

    Thanks for the reply.
  5. bntii
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    bntii Senior Member

    You got lucky.

    Kids - don't try this at home........
  6. Frosty

    Frosty Previous Member

    Very dangerous advice--don't do this. I wouldnt blow a tyre up to 80PSI let alone a fuel tank.

    This advise needs deleting. Never mind political or religious posts, this is a killer.

    No need to apply 80 PSI or anything like it , it can be pored out, then washed out and dried. Applying such pressure does nothing to remove the dirt.
  7. Angélique
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    Angélique aka Angel (only by name)

    Below looks like a better idea to me, it's not about pressurizing the tank but about sending the fuel back in high volume and under pressure to stir up the the crud and filter it out, the tank vents are open and the surroundings are well vented during the process while using separate piping for the high pressure and volume going back into the tank I guess.


    P.S. - Oh... and I agree with post #2 #3 #5 #6, as said #1 and #4 are dangerous :!:
  8. Ike
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    Ike Senior Member

    Both the USCG and ABYC specify a max 3 psi for pressure tests. I would second the comment you were lucky. I have watched polyethylene tanks be pressure tested and even at 3 psi they blow up like a balloon.

    I agree. That's exactly how I cleaned out the tank on my 1972 Sea Ray.
  9. rxcomposite
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    rxcomposite Senior Member

    Truck tires are about 45 PSI and when it burst, it is an explosion. Maybe the OP meant 80 psi in the compressor side. But he said "I pressurized the tank through the vent tube with 80 PSI". Something wrong here.
  10. Frosty

    Frosty Previous Member

    Returning fuel under pressure into the tank does not mean the tank is under pressure. This pressure return keeps the dirt in suspension so it can be removed.

    These are techniques used for cleaning internal fixed tanks and not for small tanks that can be removed, turned upside down and washed out with a hose pipe.
  11. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Can you elaborate on that? 14 years for a metal tank seems very short to me.
  12. dinoa
    Joined: Oct 2007
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    dinoa Senior Member

    If you have access through an inspection port try this. While the boat is out set up a steel barrel on the ground lower than the lowest part of the tank. Get a large preferably clear hose to siphon fuel. Those ball type siphoners with an extension work great. Ground the tank, youself and barrel and wipe the static charge off the hose with a wet rag. Start siphoning the fuel out of the tank through the inspection port while using the pick up end as you would a swimming pool bottom cleaner to suck out deposits off the bottom.
    Lighting the port entrance with a sealed divers light will help guiding the tube. With imagination and a mirror you accomplish the task even through a small inspection port. If you want to flirt with danger just once drop the grounded diving light in the tank on a string for better illumination.


  13. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    I rigged up a pump and couple filters and recirculated the gas till it got clean. On the tank with 10 year old gas, there was a sludge on the bottom. For that I rigged up a vacuum pump and glass jar and that got out the worst of the mess.
    It took months of work to get these 2 150 gallon monel tanks clean. E10 is a great cleaner to loosen up 40 years of crud. Did that with the boat in it's slip.

    Old gas tends to stick intake valves and I found the only thing that worked was adding ATF to the old gas. I put in a qt of MMO which did not stop the sticking. Then another qt of ATF which did. I had about 40 to 50 gallons of old gas in each tank at that time.

    Adding the MMO and ATF did not cause engines to smoke.
    If I took a gas sample and let it evaporate, I was left with a green clear oil. Green color maybe from all the PRI-G and Stabil that I had used over they years.

    gas sludge sucked out of tanks
    suction rig

    final recirculating pump and filters to run for hours and days cleaning the fuel. Copper dip tube sucks straight off the tank bottom. The return dumped it back in by way of the fill tube. You can see the green colored gas in the plastic lines.
    Thos lines are the hard polyetyhlene hoses you can buy from HD or Lowes. I think 5/16 ID which fit nicely onto the 3/8 rubber hose. I powered the pump using a 12 volt battery charger.
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