i bought a 1994 mazda mx6. i have been driving it for about three weeks now. just recently it started saying its over heating i thought it may be the thermostat but somethimes the gauge just jumps from operating temp to hot then back to operating temp. the other day it didnt gradually go up to operating temp the gauge stayed at cold but after dirving a little it jumped to operating tempature. could this be the thermostat sensor? or the thermo stat? im hoping the head gaskets arent bad.