Originally Posted by n4zou

It's the soap used in the mixture that makes differing types of grease incompatible. Most automotive-based grease use lithium soap but you can still have compatibly problems between synthetic and vegetable based lithium grease. Then there are the grease types with additives such as Teflon. Considering how little pressure and heat bicycle bearings are subjected too most any grease will work as long as there is no contamination present from incompatible grease or petroleum products. My favorite is Aircraft approved red synthetic grease available from aircraft supply retailers. It's impervious to water infiltration, extreme heat, and it's super slick. It's also compatible with any other aircraft approved grease types. For my bicycles I had been using it but having retired I ran out of my personal supply of that stuff and purchased a tub of green colored marine grease. In any case when I service the bearings of anything the bearings get a through cleaning with mineral sprits to remove all traces of the old grease (compatible or not) dirt, and grime. Bicycle Coaster brakes need grease that can survive high temperatures especially if the bicycle is used in an area with long steep hills. When servicing a coaster brake hub I use red colored synthetic automotive grease made for disc brake hubs as this grease is made for very high temperatures.