Be careful here. Too much oil will cause an engine to run hotter than it should. The reason is that he oil doesn't combust, and doesn't compress, so it raises the engine's compression, and that causes more heat. It may not make a lot of sense, but I've seen this demonstrated first hand.

Also, the reason I didn't suggest an overheating problem the first time was that the engine had been running fine for quite a while. If the problem was heat, I'd expect it to have shown up before. However, if something changed, heat could become a problem when it wasn't before