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Results 1 to 7 of 7
  1. #1
    Join Date
    Apr 2008
    Location
    brooklyn, New York, USA
    Posts
    31

    Default How to properly clean out fuel tanks

    Hello All,

    I have a 1978 34 foot Chris Craft CoHo with twin Chevy 350's, 285 HP each. There are two 100 gallon fuel tanks on board which cannot be removed without pulling both engines again. I have completely repowered both power plants from top to bottom EVERYTHING brand new, however, soon after the completion of the project I learned the man I bought the boat from had left 30-40 gallons of fuel in each tank for 3 years during storage before I bought it. Now as you could guess I am stalling due to clogged fuel lines. After one incident I removed the brand new Holly mechanical fuel pump and it was filled with a brown rusty scale. I was considering sticking 10 feet of 3/8 inch fuel line down into the fill-up port and using my spare 12 Volt electrical fuel pump to try to get as much gas, grime and scale out as I could. My concern is that this would leave a concentrated mess of grime, rust and gelled deposits on the bottom of the tank compounding the problem. I initially tried to run the fuel level down to approx 20 gallons and then tried to dillute the problem by adding 20 gallons of fresh Hi-octane and cleaned out all the lines but still had the same problems after 20 minutes of running. Anyone have an idea on the right way to get old gas and crap out of these 2 huge tanks?

  2. #2
    Join Date
    Sep 2010
    Location
    Germany
    Posts
    19

    Default Re: How to properly clean out fuel tanks

    Hi Ep... I have the same problem with my 75 35' Aft Cabin. I have the Chevy 350's with 235 Hp. Both engines start-up and run great upto 2800 RPM....Then thay both start to stall out but do keep on running after I pull back the power. I've looked into one ot the Tanks and found a couple of rust spots inside.The inside of the tank has like a powder on the tank walls. Might be rust... I also have brown sediment in the Filter bowls after less than one hour of ops since the last cleaning. My plan is to try to suck all the remaining fuel and sediment out with a hi-power pump, ( I have a "Gasstation" fuel Pump air driven) , and retry. If this fails then I need to reseal the tanks or replace them. There is also the option to shorten the fuel suction pipes in the Tanks. But this won't really take care of the problem....I'll keep you posted on my results.
    Johnscott

  3. #3
    Join Date
    Feb 2009
    Location
    Lindisfarne, Tasmania, Australia
    Posts
    452

    Default Re: How to properly clean out fuel tanks

    I think that you are going to have to bight the bullet and remove the tanks for proper cleaning, and if there is any rust inside them, build new ones out of Stainless Steel.

    The trouble with trying to clean out every spot of rubbish that is in them cannot be done with being able to flush them out, upside down and allow the crud to simply drop out.

    The best way to clean out a dirty, cruddy tank internally is to fill it with a quarter of a bucket of 1/2" Blue Metal aggregate, and shake the heck out of it. This will act as al internal grit-blasting, and after a while, will need changing, and emptying again and again.

    I have had good results tying a tank to a cement mixer bowl end and let the rotation do the hard work. I have never seen a clogged up cement mixer bowl, and the stones will do the same to the tank. Will need to change positions, and make sure that the lashings don't come loose, or things WILL get messy.

    One thing with Petrol Tanks is that you can't use plain steel, or they will rust out very quickly. Okay with Diesel, but Petrol requires either the internals be tinned, or Galvanised.

    Bruce.

    PS. I don't recommend the internal sealing with the auto type liquid sealers that are available, as they do not stick in some cases, and constantly cause blockages as the stuff breaks down.

  4. #4
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    7,200

    Default Re: How to properly clean out fuel tanks

    Suggestion, but at your own risk:

    Pull the fuel tank dip tubes and remove the screens.
    While I won't publically recommend removing the Anti-Siphon valves, note that these can easily become restricted when yuckies are present.
    The thread size/pitch is standard to that of a brass barbed fitting.
    The Anti-Siphon valves are there in part to protect against a fuel line/hose failure that may cause a fuel siphon.
    New hoses would certainly take some responsibility away from an Anti-Siphon valves.
    (note how I skirtted away from that one! )

    Install a pair of Parker RACOR true water separating fuel filters...... It doesn't get much better than RACOR.
    Depending on whether or not you have seen some fairly large yuckies floating in the fuel, you may need to pull the 90* fittings out and clean them occasionally.
    You may even replace the 90's with a more smooth, less restrictive, longer "sweep" 90.
    Keep a close eye on the filters.

    Educate yourself on some of the fuel additive products.

    Anything to avoid removing the fuel tanks since you have described that this would require a lot of work.

    In time, the problem will eventually correct itself, and you can re-install _________________________.

    Again.... just a suggestion.
    Last edited by RicardoMarine; 04-19-2011 at 01:18 PM.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  5. #5
    Join Date
    Apr 2008
    Location
    brooklyn, New York, USA
    Posts
    31

    Default Re: How to properly clean out fuel tanks

    thanks guys,

    I went to the marina mechanic with my dilema and he used a shurflo heavy duty fuel pump and sucked all the fuel out dry. He then added another 5 galons of fresh gas sloshed it around and sucked that out. He tells me my problem should be fixed as the last 5 gallons came out clear. Tomorrow I will change my oil and spark plugs and add some more fresh gas and see what happens. Hopefully the problem will be resolved. I will let you guys know if this method worked. Stand by, I should know for sure by monday the latest. Thanks for all the input

  6. #6
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    7,200

    Default Re: How to properly clean out fuel tanks

    I still recommend that you remove the dip tubes and the anti-siphon valves, and at least examine the screens and the check ball operation.
    This is free to do!
    I'll also still recommend that you install a real true Marine water/fuel separating filter..... i.e., RACOR.
    This is being offered to you from experience, not speculation or theory.

    I wish you a good sea trial.
    Post back!
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  7. #7

    Default Re: How to properly clean out fuel tanks

    I have a 1976 Coho and had the tanks cut out and removed. Replaced with two 50 gal plastic tanks which is enough for lake use. New tanks will fit through rear hatch if ever need to be replaced...plus I gained a lot of storage space below hatch. Had to build bracing for aft deck after removing tanks.
    Quote Originally Posted by ep_brooklyn View Post
    Hello All,

    I have a 1978 34 foot Chris Craft CoHo with twin Chevy 350's, 285 HP each. There are two 100 gallon fuel tanks on board which cannot be removed without pulling both engines again. I have completely repowered both power plants from top to bottom EVERYTHING brand new, however, soon after the completion of the project I learned the man I bought the boat from had left 30-40 gallons of fuel in each tank for 3 years during storage before I bought it. Now as you could guess I am stalling due to clogged fuel lines. After one incident I removed the brand new Holly mechanical fuel pump and it was filled with a brown rusty scale. I was considering sticking 10 feet of 3/8 inch fuel line down into the fill-up port and using my spare 12 Volt electrical fuel pump to try to get as much gas, grime and scale out as I could. My concern is that this would leave a concentrated mess of grime, rust and gelled deposits on the bottom of the tank compounding the problem. I initially tried to run the fuel level down to approx 20 gallons and then tried to dillute the problem by adding 20 gallons of fresh Hi-octane and cleaned out all the lines but still had the same problems after 20 minutes of running. Anyone have an idea on the right way to get old gas and crap out of these 2 huge tanks?

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