My Dodge Dakota has wild swings in temperature (according to the temp gauge). I replaced the radiator recently and have new hoses and thermostat. In addition, the heater doesn't work. When I open the radiator cap, I notice that the temperature cools when the coolant "burps" (when coolant comes out the upper hose). Could this be a water pump problem? The pump doesn't leak. Also, the upper hose doesn't get hot.