The coolant would not circulate threw the system right if it bad. I had one of blades break off it and it didn't move coolant properly in the system. I had no leaks of any kind. It just froze up one day
Some if the signs are: weaping from the pump, if you remove the radiator cap while the car is running the coolant won't be moving. While driving the temp will be normal, when setting still temp will rise.