I have been looking around the net for the answer to this exact question. We just purchased a 1992 STS, and I wanted to make sure at what temp we should get concerned. The person who sold it to us was a service advisor at a local repair shop, and he told my wife if it reached 220 degrees pull over and let it cool down.
While I respect his knowledge, it seemed to me that 220 wouldn't warrant having to pull over. It has reached this temp a few times, with no smells, noises, that one might expect from overheating.
I would truly appreciate if someone might be able to tell me what I might want to look for as far as temps under normal conditions in SoCal.
220 is not a problem for these cars. Most new cars run hotter than that in stop and go traffic. The low speed fans on the 92 Seville won't even kick on until about 225 degrees F.
My 92 STS runs at about 198 on the freeway, or when I'm driving it at a speed that's actually cooling off the radiator. In very bad stop an go traffic it'll hit 225 all the time, then go down to about 215 where the fan kicks off, but it never gets above 235 (I think the high speed kicks on at about 230 or so).
I'd say if you hit 240-245 you should pull over and shut it off. That's too hot.