200 degrees is fine and normal for a 400 with A/C in hot weather with the A/C off. Mine does fine at that temp in gear in stopped traffic for hours during the Dream Cruise, the only complaining component was the trans as the trans fluid was not cooling sufficiently. If you don't typically sit idling in traffic for hours, you won't have an issue.
Some signs of an unhappy hot 400 are rougher and louder than normal sounding exhaust, possibly some stumbling, slow trans engagement (auto), burping coolant (you can smell the antifreeze even if it's not dripping) and loud ticking when you shut down.
After you've hit 210 and continue driving at normal speeds, how long does it take to drop back to 200?
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
