I did my rear axle seal job today. The guy at Oreily told me I need 1.5 quarts of differential oil. So I got two bottles (1 quart per bottle). After I got home, I started to fill my rear axle. I read somewhere that fill oil till it come out from the filling hole.... But I fill two bottles, there is still no oil coming out... Maybe it's because my truck's rear tire sits on a ramp?

Anyway, did I add too much oil (2 quarts) or not enough oil? If too much, what will the harm be?