It could be a blockage in your radiator , your thermostat , head gasket.
Mostly likely your thermostat is worn out and is sticking closed.
Replace thermostat and check.
Your radiator and have blockage. You need to flush it and check the inside of it visually for any corrosion build up. Replace fluid and add the proper amount of antifreeze.
Antifreeze also cools your engine, and has anticorrosion properties as well as stops it from freezing.
Headgasket is major problem and should be taken to a service dept for repair.
Mitchboogie, July 2005