Re: 20 year old Coleman stoves
I have a three burner Coleman stove that's over 36 years old and it lights right up. I just recently used it a little over a week ago. It only gets used once every other year and I store it full of fuel. One bad part of regular fuel are the additives (including ethanol) and dye that turn old fuel into a varnish like substance that plugs small orifices. Coleman fuel is pretty pure, for the most part, so it doesn't suffer quite as bad, however, it must be kept where it can't absorb moisture.
I have used five year Coleman fuel without any ill affects. I can't say the same thing about automotive gasoline, where I have seen it gel in just months, especially if it can attract moisture. That's why I ALWAYS use a fuel stabilizer, like Staybil, in all my fuel containers as soon as I fill them. Fuel left in my commercial mower, lawn tractor, generator, and other small engines (chain saws, string trimmers, blowers, etc) all have fuel stabilizer added.