1967 Mercury Cougar cAR RUNS HOT WHEN STOPPED AT TRAFFIC LI

MY 289V8, IN MY 67 COUGAR, SEEMS TO RUN HOT WHEN I AM STOPPED AT A TRAFFIC LIGHT. WHEN I AM DRIVING IT SEEMS FINE. IF I STOP THE GAUGE STARTS TO RUN TOWARD HOT, BUT NOT IN THE DANGER ZONE. WHEN I START UP AGAIN IT SEEMS TO COME BACK DOWN. Some have told me that this is normal in older cars. One other thing, if the A/C is on it runs hotter as well.