The oil just gets thinner as it heats up. The engine also gets looser as it heats up. With everything expanding the thinner oil leaks thru the bearings easyer. Its nothing to worry about. The **** most likely just has a different type of sender and gauge. I have a factory gauge and add on mechanical gauge in my 85 Dodge. The factory gauge hardly ever moves from the green, but like your engines, the mechanical moves from 15 to about 50 once it warms up. Its just normal engine stuff. Thicker oil would help some. Joe
