Temp guage, up & down, up & down...

My son's 1997 Monte Carlo just had the water pump replaced. Now from virtually everytime he drives it, the temp guage will spike to almost the red line, then cool off again, then spike back up, ect, ect. Any ideas

sounds like a classic case of trapped air in the cooling system. Did you replace the water pump or did a shop? If a shop did it bring it back and tell them about it. If you did it, bleed the cooling system. If that doesn't work, you have problems elsewhere.