Dear Cliff, You have to bleed the air out of the cooling system. Air trapped in the system can cause damage to the engine. The bleed screw is on the top of thermostat housing. There are several methods to bleed the air out of the cooling system. According to the DeLorean World Technical Index (1996), the procedures are covered in DeLorean World Vol. 4 # 1, Vol. 6, # 3 & Vol. 9 # 3. Sincerely, Mike