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  1. #1

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    Ways to check the gas tank for leaks

    I pulled my gas tank on my 93 SL750 and discovered there was gas on the bottom of the hull. I'm not sure if it was from me wrestling out the gas tank of if there is leak in the tank. Prior to me wrestling out the tank I had not smelled any gas. I did pour out the remainder of the gas and visually confirmed if there were any signs of leakage. My question is how do I test the gas tank for leaks? I do have the tank out of the hull.

    Cheers in advance!


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Pressurize the tank with a few PSI air pressure, then spray soapy water all over, look for foaming bubbles at leak points.

    Do not use huge air pressure, just a few PSI so you don't split the tank apart.

    Also check the gas filler neck and cap for hairline cracks. Same for the fuel tank sender top fitting.

    Fuel selector valve should be replaced if original.

    Fuel/water separator may need new seals, if your model has one.
    Last edited by K447; 11-03-2014 at 10:11 AM.

  3. #3

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    All the gas is in the front part. I know I spilled some getting the tank out, but the amount on the bottom I don't think is consistent with what I believe to be true. I have checked the cap and neck, both look fine. The neck looks like it's been replaced before, seems, newish. Fuel/Water separator, I don't think I have one (93 SL705) How would I pressurize the tank with the neck being open?

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Octoarms View Post
    ... How would I pressurize the tank with the neck being open?
    Use the OEM filler hose and find something that will cap the hose opening. Attach with hose clamps. And remember, the air pressure is going to try to push that cap/plug out, so don't be standing over it with pressure in the tank.

    You only want a few PSI for leak testing, don't over inflate it like a ballon.

    The factory pressure release check valve (which are connected to the fuel tank sender VENT hose fitting) typically opens at about 2.5 PSI. You can use a bit more air pressure than that, but not huge.

    I generally use the VENT nipple to apply the air pressure and loop the other nipples together or cap them off with short hose sections.

    The overall process is very similar to doing a leak-down pressure test on an engine.

  5. #5

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    My original idea was fill the now empty tank with water and let it sit in a dry area. If the area is still dry I can rule out a leaky tank. I'm not sure I have a plug big enough for the filler neck.

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by Octoarms View Post
    My original idea was fill the now empty tank with water and let it sit in a dry area. If the area is still dry I can rule out a leaky tank.

    I'm not sure I have a plug big enough for the filler neck.
    Plastic plumbing dept at your local hardware store. There are caps for various sizes of plastic drain pipe, I imagine something would fit well enough.

    Water leak method may work, depends on how quickly the water evaporates after it leaks out.

  7. #7
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    Air will pass through a breach before water. Water is a poor test.

  8. #8

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    I do have UV dye I could use from when I had a coolant leak in my truck. But I'll also look into doing the pressure test too.

  9. #9
    BlueFishCrisis's Avatar
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    You'll want to check the fuel level sender gasket too. The screws holding the level sender in can strip out causing a poor seal, as can a damaged rubber gasket.

    You can easily add a fuel water separator with integral filter from a later model ski, if desired......

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