How hot can you safely run a Chevy 350?

i would not go much over 220 its pretty hot, if u have to run it hot its safer to use full syntheitc oil. If its running hot for some reason u may want to change the thermostast, give the coolent system a flush, and make sure the fan clutch is not worn and is pulling enought air. If its electric fan make sure there coming on. The hotter the engine is the thinner the oil gets and the engine will wear out sooner. Its not good to run them to cold either, but hot is more dangerouse. I have a sbc 350 and the most it gets on a hot summer day with the ac on, and not moving is around 210 or 215 tops . If yours is running 220 or hotter with nothing on or on a hot day u may want do somthing. If everthing in the sytem is good and clean working properly even the water pump, you may want to get a more heavy duty fan clutch or get a more heavy duty radaitor.