how can you tell if the water pump is bad on a 93 k1500 350.water temp goes up to 220 and it will drop down to 180. pull termostat out and it still does it.any help.

first with a cold motor take rad cap off. doesn't matter if thermostat is in or not. let it run till it gets hot and look in rad to see if you have flow. if no flow then problem is probably the radiator needs a good flush or taken and have it cooked out also good idea to flush block as well.