Within the last 30 days my mechanic replaced the radiator, radiator fan and themostat yet the temperature guage continues to fluctuate and eventually overheats. This appears to happen when I come to a complete stop and comes back down while driving. My mechanic is NOW telling me, it's the head gasket. After putting close to 2k in his pocket last month, I don't feel comfortable paying him another dime for another 'assumption'. Other than replacing the head gasket, does anyone know what else could be causing this to happen?