Meaning that the engine is not actually overheating?
It will knock under load whenever that temperature is reached, but you may not hear it (and ignore the damage).
That temperature is not the water temperature everywhere inside the engine. I assure you that the water closest to the exhaust ports, exhaust valves and spark plugs is much hotter than 210, and is only prevented from boiling where it it (not in the radiator) by cap pressure.
