170 Thermostat?

you know that test is old, look at the graph! Data courtesy Continental Motors and it as referenced in a Ford rebuild book dated 1989, but the test data graph has been around since at least a 1986 book and its probably older than that...mid 70's with same era motor oil? You wonder why these Magnums still have hatch marks in the cylinders at 120k? They ran hotter than 170 for sure, ~190? My Silverado has a working temp range up to (red) 260