my car is getting hot in traffic with ac on. it still runs hotter that it should on the highway but not that bad. has a stock radiator with 180 thermostat. i think i might have a head gasket leak. is there an easy way to find out. no coolant in oil. car has h/c/i swap. stock style fan/clutch. car would run 160-180* on cool days before this tennessee weather got hot. what is the easiest and cheapest way to add a temp guage to be sure temp is accurate?