Ford Repair: Temperature or Coolant Issue, temperature gage, clutch fan

Question
95 Explorer 4.0 When I don't run the heat or defroster my temperature gage runs normal as always. However, when I run the heat or defroster, the temp gage runs normal then spikes towards hot and comes right back down. It does this several times when the heater/defroster is running. Any ideas on what's causing this? New thermostat installed, all hoses are warm as they are suposed to be. No leaks that are visable. Any ideas?

Answer
Hello Richard, I would check to see if the waterpump is giving you enough flow. Have seen something like this before and found the fins corroed and gone on the water pump, Also check to make sure the cooling clutch fan is working. Hope this helps Thanks Tony