How can I remove white crusty stuff from old clear jars?

if the crusty stuff is a lime/ calcium build up soaking in a vinager water solution and a good scrubbing should work. If not for canning jars...lime away worked for me.

If you were to use them for canning home produce. Inspect for nicks cracks at the mouth of the jar. If you find any rough spots on the rim, mark for craft use only. The jars won't seal properly.

http://www.wikihow.com/Remove-Hard-Water-Stains-From-Glass

Dishwasher - Cream cleaner Hot water - What do you want to use the Jars for?

I just use vinegar and then rinse out afterwards

Fill with a half and half solution of warm vinegar and allow to sit at least overnight. Use a scour pad to rub out any that is left after brushing as much of it out as possible.