I agree the most important thing is all bearings run about the same temperature. If one is much hotter than the others there may be a problem. I just checked mine last week with an infrared gun after running 100 miles. They were about 100-105 F when the ambient was about 80 F. I also agree you do not ever need to add grease. Grease is not consumed and if it has been compromised by driving through a lot of water or the trailer as not been used for a long time then repack the bearings and check the brakes.