hmm I've always filled mine up to the fill plug in every vehicle I've had, generally this is right around what the fluid capacity is supposed to be(in fact both mitsubishi and Chevy told me to do this for my gsx and my vette). Filling it up to the plug shouldnt give you any problems, I need to change mine out again so I'll measure this time how much it takes to fill it to the plug. I actually use a long ass tube that i feed down thru the engine to fill up, best for gravity setup up, but the pumps are also a wise investment!