Pontiac Repair: temp gauge, blown head gasket, water temp gauge

Question
I have a 1992 pontiac lemans.  When the car is started the water temp gauge goes straight to hot and pegs out.  I have replace the gauge the sensor and the radiatior.  Why would it do this?

Answer
Something is causing it to overheat. Could be a stuck thermostat, cooling fan not working, blown head gasket, or a bad water pump.
You should probably take it in to the shop and have it checked out before you waste alot of money throwing parts at it.