This makes no sense to me...you put a little grease into a bearing cap, the bearings are looser, and they run better. Heat down.So you put in a lot of grease they should be too loose or run too slick. But that's not what happens in real life. Instead, they overheat. Why on Earth would they overheat? It's not like they are lacking needed air to cool down. Can anyone explain?
When you put grease into bearings (cone and cup of a ball or roller bearing set) it does not change the tolerance of the bearings, i.e., make them looser. The grease fills the voids between the moving parts and takes up the tolerance with grease. If bearing tolerances are too great, or the bearing lacks sufficient grease, then differential loading will cause some parts to have significantly less tolerance than other parts and there will be points of excessively high load in some areas of the working parts. This will create excessive friction and heating.
Bearing manufacturer's recommend 25%-33% fill for the voids in radial ball bearings. They cite shear, and churning as sources of volitalization of the grease which leads to loss of the lightest fractions; and reduction of lubricity. See the source below:
