[Alan Roehrich]

Get them fairly warm (150 degrees or so if possible). Soak them down several times with oven cleaner, so that the crud is saturated completely. High pressure wash them. That should get them fairly clean, but old fashioned hand labor may be required, and you may have to repeat the process. Any removal of the thick stuff before soaking and washing will help. Eagle One etching aluminum wheel cleaner will remove a lot of the stains, once you get the crud off.