2002 Nissan Sunny engine temp going high

When the coolant gets drained or leaked out. You will get air in the system in other parts of the cooling system. When you first filled the radiator after installing it. Did you fill it, leave the cap off while it was running till it reached operating temperature (thermostat open), then raise the rpm to about 3000 a few times, fill the radiator again with coolant, and check to see if you have heat. IF you did all that and you coolant was low again then you have a leak somewhere else.

Ok, when you pull the oil dipstick does the oil have a milky consistency?

Ok, have you replaced the thermostat? Seeing bubbles will be normal after first filling the the radiator when the engine is running cause it is pushing air of of the system. If you continue to see a lot of bubbles then it could mean you have a leak in the head somewhere and compression is going into the cooling system (forcing in air). The coolant will boil if the cap is off and been running for a while (dont mistake that for bubbles).

If coolant is actually boiling (not overheating) then you may just need a new radiator cap. The is meant to to build up pressure in the system (about 16psi). A fluid under pressure raises its boiling point. If the cap is faulty then it may not be holding pressure at it should. Have a new thermostat installed if you havent already to just be sure. I still cant say for sure your head is good or bad. I can only go off your info that you have provided me thus far.