I've done the service work on lots of Nissan CPJ and H models with the H20 and H20 II motors and never had a overheating problem, even with dirty radiators. I guess the first step would be to check to see if the radiator is as hot as the motor when it overheats to prove the the coolant is circulating. Sounds like it isn't circulating good due to the thermostat or maybe the head water jackets are plugged. If the head gasket is bad and blowing combustion gases into the water, it will definately have problems.