within seconds of start the radiator starts filling the overflow. i just got a new radiator cap, 16 lbs on a diesel radiator that is attached to a 350 engine. after a while it stops overflowing and when it cools off it sucks fluid back in. my question is, isnt the overflow not suposed to fill unless your overheating. and how can i be overheating seconds after start up? could it be my fluid has been watered down too much? it still is green, just not solid thick green.