Radiator putty is usually different than what I'm talking about. What I keep here is specifically for fuel tanks and will last a long time. You will need to determive your real problem first because like said above, it won't fix a rotten tank. It will, however, fix any puncture holes. The biggest I have ever used it on was about the size of a quarter, it took 3 but got the job done. If I remember right it is a permatex product and much less than a new tank. I would suggest a new tank at some point also, but if it's just a tank with a puncture wound, the putty should work well until you can figure out what you want to do.