I have a 2002 Cadillac Deville and the fans work the coolent reservoir is always empty the next day and when I drive it runs hot

You have a coolent leak somewhere in the system. I have a recommendation you can try but no promises try add some Alumi Seal Stop Leak to the radiator works great most of the time. If vehicle does not have a radiator cap remove top radiator hose with vehicle cold add sealer into hose then reconnect the hose and follow directions on product.

Im no expert but i wouldnt put the alumaseal quick fix in your car unless absolutely neccesary. It could clog your cooling ststem. I would start off by doing a pressure test of the cooling system and observe any leaks. These motirs have bypass tubes and hoses that are hidden and you wont be able to see just by looking. Pressurizing the system will help locate in a area of where the leak is if there is an external leak.

Alumi seal will not clog up your cooling system unless you use more then that is recommended. In other words if it does not work do not continue to add more hoping it will work.

The coolant has to go somewhere. It either leaks into a cylinder and exits as exhaust (head gasket or cracked block) or it leaks out onto the ground (many possible locations but best seen by doing the pressure test recommended by Johnny).

I'm going to try removing top radiator hose on my 2000 Seville put alumaseal in that way. Have leak along seal