What cause a car to overheated when you replace the water pump an thermostat?

It's possible that your fan may not be kicking on. To check if your fan is working on your car, turn your air conditioner on, your fan should come on at that time. If it does, you may need to look at your censors that control your fan. Also, make sure that you do not have any leaks in your hoses leading from your motor to your radiator. Hope this helps!