Nissan: 2002 Altima, Temp gauge fluctuating,heater runs hot and cold, head gasket problem, radiator hoses

Question
I have an 02 Altima 2.5 S. A few weeks ago I noticed that the heater runs hot and cold. Sometimes it blows hot air and then it turns cool. Today I noticed the temp gauge fluctuating between middle of gauge all the way to H, then back down and up. Could this be a thermostat, heater core or head gasket problem. It was a cold rainy day today so I could not tell if there was excessive smoke coming from tailpipe or not.

Answer
HMMM, not sure. Fill up the radiator to the top, stick a funnel in the filler hole, one that seals the hole. Fill the funnel with water and warm up the engine. WIth water in the funnel there should be no bubbles. You may see some at first but they should go away. Make sure both radiator hoses get hot. If they do not then I woud replace the tstat. Loss of heat and overheating is usually loss of coolant.