Engine Running too Cool?

Before you get to worrying too much one way or the other, check it with a thermometer. Then decide on a course of action that will keep it in specs. Any sort of wear from too much or too little heat is all relative. Even the amount of time it spends in certain heat ranges, like warming up or cooling off all count. If it could go 500,000 miles and you only get 470,000 does it really matter?