Excessive Cooling
 

My 98 Dakota with a 318 has excessive cooling issues. I replaced the water pump this past weekend cause it was leaking and along with it I put in a new thermostat and the operating temperature is around 150. The coolant system has no air in it and it has the proper coolant levels. My dad thinks it’s the radiator fan and that it is enhanced causing excessive cooling. I heard you are suppose to replace the clutch fan the same time as the water pump. Could it be something else? I have not flushed the system but the heater core lines coming out of the firewall are both warm. One thing I noticed is that after running it for about 20 minutes the return line to the radiator is still cool. Any coorilation?
thanks