This happened back in 1973 when I first purchased my 1969 Z/28 RS. I was 22 years old at the time.
Late one evening, my good friend, Bud, and I had just finished installing a new clutch, repainted and re-installed the headers, adjusted the solid lifters, and numerous other needed maintenance items. We also polished the chrome factory air cleaner and valve covers. Engine bay looked like new!
After adding new anti-freeze and rechecking everything, we decided a test drive was in order even though we were both dead tired. So off we went both keeping watchful eye on the factory gauges on the console as I drove. We came to a traffic light just as it was going amber and decided to pull into the closed, darkened service station to take a peek under the hood. Bud was out ahead of me and had the hood up. I was getting out when Bud yelled, "Shut it off! It's hot!" I wondered how it could be possible as the gauge, which functioned well, read about 180 degrees.
So I shut it off. Bud pointed to the engine which was glowing red, not only the valve covers, but even the air cleaner. We both held our hands over the engine and felt no high heat coming from the engine. I touched the valve cover. Just as I did, everything that was glowing red turned green! The traffic light the car was facing had turned! The colors were reflecting in the polished valve covers, air cleaner and other polished under-hood parts. Our young faces both turned red at this point. We have never told this story until recently. Now we can sit and laugh about it and we are both old and can take the "heat".