'94 chevy caprice radiator

My Caprice's radiator doesn't have a radiator cap on top. The gauge has been reading hot at times and I have to refill the plastic radiator fluid overflow tank. Where do I go to fill the radiator or check the fluid level?

Thanks.

The expansion tank is the only place to fill the system and monitor the cooling system level. It is not simply an overflow tank on the LT1/L99, but is an active part of the cooling system, under constant system pressure. It's just like the space at the top of the radiator in an older system.