1996 cadillac eldorado

Take it to your mechanics shop, they can do a drop of coolant and put fresh in. Also put a new thermostat and/or water pump.

Or read owners manual find out which coolant to use and overflow reservoir location and top off as required by marks on side of it. Then, if it still evaporates follow answer# 1's advice.

if you dont have access to the radiator it means the reservoir (Tank of extra coolant), is physically higher than the radiator, and gravity itself feeds the system., make sure that is at the required level.

you probably need to back flush the coolant system to get sludge out of the bottom of the rad and replace using a good quality antifreeze,you do this easly via the top and bottom hoses,but make sure you know where the header tank is by refering to the handbook