Tank rust sealing issues :(

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  • wirelessguy
    • Feb 2026
    #1

    Tank rust sealing issues :(

    I've been on/off this forum for some time now. Been spending the past few years restoring an old GS bike (sadly more time wrenching than riding).

    I've been traveling this summer and haven't had a chance to ride at all. I decided to check on the AGM batter yI have in it and was able to get it charged up just fine and started up. She ran a bit rough, which was not unexpected on my end.

    I opened up the gas tank and my heart sunk a bit.

    I had stripped down the inside of the tank and coated it with POR-15 (also did rust inhibiting paint job on the outside and repainted the tank nicely).
    Anyhow, when I looked into the tank I saw a ton of bubbling/rippling

    I was pretty sure I gave the tank plenty of time (more than a week) to cure before putting any gas inside. Perhaps it was the engine heat after running the bike for a while that baked in the inside of the tank. I'm not really sure.

    Can anyone out there give me some opinions on what might have happened and how I can avoid this again?

    I'm really not happy that I'll have to unmounted and protect the paint job on the outside of the tank while going through a process like this once again. Looks like I may have yet another winter project ahead of me.

    Thanks.

    photo2_zps340e35e4.jpg
    Tags: por-15, rust, tank
    • Rob S.
      Forum Guru
      Past Site Supporter
      • Dec 2013
      • 9395
      • New York City
      #2
      I saw an interesting video on cleaning tank innards.

      1. Make sure the Mrs. is out of the house.

      2. Put in the tank a pile of nuts, bolts, washers, etc.

      3. Wrap the tank well in blankets, quilts, etc.

      4. Put it in the dryer (no heat) and let 'er rip.

      A few minutes later, the inside is shiny new, the lady of the house is none the wiser.
      1982 GS1100E V&H "SS" exhaust, APE pods, 1150 oil cooler, 140 speedo, 99.3 rear wheel HP, black engine, '83 red

      2016 XL883L sigpic Two-tone blue and white. Almost 42 hp! Status: destroyed, now owned by the insurance company. The hole in my memory starts an hour before the accident and ends 24 hours after.

        Comment

        • chewbacca5000
          #3
          As far as tank liners are concerned I like Red Kote the best. Por 15 and creme are good, but will not fully cure if even 1 drop of sweat gets in there. You can use Acetone or MEK to remove the old liner. Remove petcock first as these will destroy the o-rings or rubber. Do not let acetone or MEK touch paint at all will eat it.

          After a 24 hr acetone soak the old liner will come out in sheets or strings. You may need to strain the acetone and repeat.

          Nuts, bolts dry wall screws work good to cut remove any remaining residue. I would not shake tank with acetone and nuts and bolts in it too great of a risk of spark

          Just let er soak.

          RedKote has been around forever and is alcohol resistant up to 20%. Absolute easiest to apply. Just get tank super clean with power washer or other method then use a little denatured alcohol to get water out. Make sure tank is 100% dry inside before appling RedKote. If MEK is available RedKote can be thinned a bit for more even coverage and better drying. If thinning 2 to 3 coats are in order. Good stuff.

            Comment

            • bille
              #4
              Originally posted by Rob S.
              I saw an interesting video on cleaning tank innards.

              1. Make sure the Mrs. is out of the house.

              2. Put in the tank a pile of nuts, bolts, washers, etc.

              3. Wrap the tank well in blankets, quilts, etc.

              4. Put it in the dryer (no heat) and let 'er rip.

              A few minutes later, the inside is shiny new, the lady of the house is none the wiser.
              #1 is the most important step and should not be skipped no matter what!

                Comment

                • 81GS850
                  #5
                  Can you tell us what coating you used? I got all the rust out of my tank and left it bare. Sometimes I think about coating it, then i see these issues. If the bike is ridden a lot then there's not need for a tank liner. Also have you tried maybe electoplating the tank inside instead of a paint? This would be the best method.

                    Comment

                    • 60ratrod
                      #6
                      from the research that i've done, i've seen that oxalic acid does a good job of removing rust and leaving a protective layer that is also good for applying a coat of liner. i like the drier idea though. since i'm the one and only in my house, i just need to make sure that i'm out in the garage for 90 minutes while my tanks to their thing

                        Comment

                        • 81GS850
                          #7
                          Originally posted by 60ratrod
                          from the research that i've done, i've seen that oxalic acid does a good job of removing rust and leaving a protective layer that is also good for applying a coat of liner. i like the drier idea though. since i'm the one and only in my house, i just need to make sure that i'm out in the garage for 90 minutes while my tanks to their thing
                          Phosphoric acid is supposed to leave a film too and I can personally vouch that it'll clean rust up no problem. However it didn't really leave a protective layer like it said it was supposed to. I got some flash rust fairly quickly.

                            Comment

                            • 60ratrod
                              #8
                              phosphoric is for mild-heavy build up, and the product it leaves behind is perfect for applying a tank liner, but if you leave it untreated, it will start allowing sediment to flow into the fuel and clogging jets. oxalic acid just leaves a galvanized looking coating, that is also great for applying tank lining compounds, but will beggin rusting again if left untreated, just like any steel tank on the market.

                                Comment

                                • 81GS850
                                  #9
                                  Yea I have an inline filter catching all that. I am thinking about doing a red kote tank liner.

                                    Comment

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