Nissan Repair: car boiling back in over flow jug, spark plug heat range, water coolant

Question
change thermostat new radiator fans come on boils over lose heat when sitting still good heat when driving

Answer
As you drive, the water flow increases and moves faster in the heater core. Seems there is a water flow restriction that prevents the water, (coolant/antifreeze, never use plain water) to circulate and it can very well be in the heater core. Other causes could be a retarded ignition timing which will cause the motor to overheat, wrong spark plug heat range and improper engine adjustments.