98 Cadillac Eldorado HELP

The hard start, coupled with the smoke and coolant consumption suggests an internal leak. The overheat is another indicator. To confirm this you can have a block test for the presence of combustion gases in the cooling system. Since you have quite a few miles on the vehicle, you may opt to have it repaired, as that may be the most inexpensive route. The problem is, having the trust in the person working on the vehicle, and that they are going to restore it into factory condition. A major repair performed by the wrong person, can lead you to continual problems, expense, and frustration. The proper repair would include the installation of thread inserts to restore the threads in the engine block, a common reason that the leak occurred in the first place. There are special tools that have been created for this procedure, and they do work. If you were to get 1)a used motor or, 2) a rebuilt, there is no guarantee(or way to tell) that the thread inserts are there. With that amount of miles, and since the powertrain has to be disassembled, you may also consider having other procedures done, to take advantage of the long term savings in labor. Things like oil leak correction if the lower crankcase is leaking, transmission repairs, etc.