Moisture in fuel?

A friend of mine has a 1989 XJ with a strange problem. Sometimes when he is low on fuel it won't start unless he puts in some of that HEET fuel treatment stuff. This morning he ran out of gas put four gallons in and it still wouldn't start. It turns over but no starty. We add the HEET and bingo, it starts right up! How in the world is moisture getting into every tank of gas? Does this HEET stuff take the moisture out that quick? How can moisture get into the tank? He uses BP gas most of the time, and when it runs it runs pretty good.

Thanks guys!

Burley

Personally I think that the underlying problem is a sticky/weak fuel pump or possibly a clogged fuel filter. The filter being the most likely. The heat contains alcohol and will tend to free a sticky pump or take just enough sludge out of the filter to allow it to pass fuel. When you turn on the key, do you hear the fuel pump run? Does it quit after a few seconds? It should. Moisture in the fuel, unless you have a large amount, won't keep it from firing at least some of the time. The fuel