RE: 97 Deville cooling system
Check the coolant by pass hose from the holding tank to the block. It can plug up over the years and it wont burp properly. Remove the hose, engine off, and make sure the nipple at either end is not plugged up with debris. Very common issue with the northstar. When I fill a cross flow radiator, I have a friend hold the engine rpm above 12 to 1300 RPM while I add the fluid. Once full wait till the thermostat opens and the coolant will drop quickly. Keeping the fast idle, top off the radiator and quickly install the cap.
2 1984 Eldos, 1991 Allante, 88 Allante (sold)