[G.M.]

You can run 100 lb cap and not have a problem until you have an over heating problem. The hotter it gets the higher the pressure in the system gets. First the radator tank will pucker up and then something will break and steam and hot water will shoot out. This can burn or harm the person it comes in contact with. A 4 lb cap is all that is required on these engines. A 4 lb cap will hold pressure produced by about 212 degrees. The pressure cap seals the over flow tube and allows the coolant to be filled up to the filler neck provideing better cooling and stops the lose of water. The cap is also a safety valve that opens at 4 lb pressure releaveing the pressure in the system. Pressure can also be interduced in the system by a compression leak. Again I caution that most pressure caps don't seat at the bottom. G.M.