"You don't give the year o
"You don't give the year of the engine but 160 deg. F. is the temp some newer models run. When you pull the dipstick is there some foam or bubbles at the top of the stick? Is the oil on the stick gray or milky? How often is the engine serviced?
Just to be sure there isn't any water in the oil, w/the engine cold, loosen the oil pan drain plug enough to allow a small amount of fluid to come out. Water will be the first thing out if it is there.
I've seen the same thing on my vehicles between oil changes. If the oil level never rises above full then it is most likely condensation; I wouldn't worry about it. Clean the cap and hoses w/carb cleaner and go boating."