What is the best operating temperature for a small block? My daily driver '55 Chevy has a stock-type radiator in it. I drive it regularly in the heat here in N. Florida, and I use the A/C sometimes when it's really hot. I've noticed on the hottest days when I'm sitting in traffic, the temperature can climb to almost (but not quite) 220...that makes me a bit nervous. So, at what temperature should I be concerned?