Nissan Repair: ENGINE BOILING, radiator caps, nissan cars

Question
Recently whilst driving on a cold night i noticed the engine temperature had risen well above normal.This was the second time happening.I stopped in the middle of the journey and decided to add more water to the radiator. I waited for the engine to cool down and then decided to open the radiator cap.In the rush of things i lost the cap.Since the next garage was 10km away i decided to just seal the radiator temporarily with some plastic that i had.Less than 5km down the road the temperature had gone extremely high again.I had no option but to stop.I then hitch hiked to the next garage and bought a raditor cap.I then continued with my jouney but twice stopped to top the radiator as the engine temperature was continously above normal.My car has never been the same.The temperature is always higher than normal sometimes reaching very after a few minutes of driving.I have done everything, clean the radiator,remove the thermostart and tested for possible head gasket burnout.What could be the problem?  

Answer
Kennedy,

Lets baseline the cooling system first.  Replace the radiator cap with a factory Nissan unit and purchase a new Nissan thermostat.  After installation and filling the system up with a 50/50 mix of demineralized water and anti-freeze see how things work.  The system should be normal.  If not, check that the electric fan works properly.  And, if not turn the airconditioner on and see if that makes the fans come on.  If so, replace the relay for the fan on the temperature sensor side.  If not, replace the fan motor on the radiator.  Make sure that you do not have trapped air in the system.  You did not say what model you have so I do not know the configuration.  But, many Nissan cars have specific bleeding procedures to get rid of trapped air in the system.  Also, the next time you have the car getting hot turn the heater on to aid in the cooling process.  I like NISMO radiator caps since they have four pounds more pressure and help prevent overheating.  However, the increased pressure in the systemm can cause weak components to leak or pop.  So, if the system is not iin good working order just go with a factory cap until you can get all components renewed.