Nissan Repair: cooling system, head gasket problems, center bolt

Question
car started overheating about a month ago.I changed the radiator&themostat,I had no visiable leaks or no coolant coming out of the tailpipe,so that ruled out the waterpump or head gasket problems.I have a 93 infinity Q-45.Do you know if this vehicle has a drain plug that I must disengage to release the steam and air out of the engine housing.I would appreciate anyones assistance

Answer
Kevin,

Yes, the system has to vent the air from the system.  If you check out the upper hose at the engine you should find a vent bolt on the housing.  It is a ten millimeter and all you do it open it to let the air out of the system.  Do this with the engine off and the radiator cap off.  The air will be forced out of the system.  Now that you have done it once run the car until it reaches temperature and let it cool off and repeat the process until water comes out around the threads.  Do not remove the center bolt all the way or it will be a pain to reinstall.  All you need to do is loosen it enough until the air comes out.  Also, did you replace the radiator cap?