Over heating

You may have a bad radiator,or your head gasket has blown.

Could be blown head gaskets. Also, it's an older vehicle, so the engine could just be bad.

The thermostat shouldn't be removed for overheating unless it has failed to open at proper temperature, your cooling system doesn't benefit from removing it, you may have other issues such as clogged rods in the radiator or plugged and clogged water jackets in the engine as we'll, prolonged driving while overheating the engine will cause major damage such as TST and Ares26 have stated.

When thermostat is removed and not replaced, your radiator doesn't function as designed, it keeps coolant in the radiator to be cooled until the thermostat opens to allow coolant to cycle properly.

There is hope for your NORTHSTAR ENGINE if it overheats and has blown head gaskets. I spent 5 months researching the problem and finally found Norm Huhn who manufactures the inserts needed to fix the aluminum heads and keep them attached to the steel engine block. After I finally figured out what the problem was on my wife's 2000 Cadillac Sedan Deville, and after wasting my money on what's called the TRIPLE PLAY, (replacing the water pump, the thermostat, and the crossover upper gaskets) coupled with the use of a liquid sealer (which never works) my mechanic told me not to throw any more money into this car. Hogwash, since in my heart, I knew that was the proper way to fix the problem and a good mechanic somewhere out here who knows how to do the job right. Even my own local Cadillac Service Manager was in denial about this engine's inherent manufacturing problem from 1999 through 2003. Norm gave me 3 good leads, all within 30 miles of where I live, and I chose the one guy who had no-call-backs on any of his Northstar Head Gasket repairs. YES, it is a lot of work! A full day to remove the engine from the bottom of the car, a full day to break the engine down and drill out the 20 new slots for the Huhn inserts, replace the gaskets, and torque the new bolts, and another full day to reinstall the engine. The fix turned out to be a steal at $3K since where would we be able to get a Cream Puff 2000 Cadillac Sedan Deville with only 68,000 miles on it for that amount of money, or for that matter, and other good reliable used car? As it turned out, our car also needed new front brake pads, 2 new front rotors, a new power steering pump, a new starter, and a new E-Brake release contact, which my wife and I were well aware of. The same EXPERT Cadillac Mechanic charged us another $1K to do all those repairs too. And now, my wife's Cadillac runs just like it did when she drove if off the dealer's lot 17 years ago. You can contact Norm at his website, http://www.huhnsolutions.com/ And you can reach me at toetoe1@aol.com for additional info if you live in the tri-state region of NY, NJ, or CT.