What is little pump behind thermostat on 94 Cadillac Seville 4.8 north star eng?

That little pump behind the thermostat on a 1994 Cadillac Seville with a 4.8L Northstar engine is the water pump. While it's not directly *behind* the thermostat in the sense of being completely hidden, it's closely associated and often in a position where you might see the thermostat housing before noticing the entire water pump.