What you are experiencing sounds normal to me.
We must review several key properties of water to understand what is happening here:
1) water expands when temperature rises. If you run the engine with the pressure cap off, the temperature of the water will rise, and the water will expand, if you shut the engine off, the water flow in the radiator stops, and heat transfer to the air is halted, the water will instantly start to expand in proportion to the amount of heat that was put into the water by the engine.
2) The the hoses will feel hard when the pressure cap is installed and the engine is run to operating temperature, the cooling system is designed to hold pressure to about 16psi.
3) Water boils at 212 F @ sea level, and will boil at a lower temp. as altitude increases (lower atmosphere pressure). The pressurized cooling system raises the boiling point
of the engine coolant, this allows the water to remove more heat from the engine. The higher the pressure rating of the cooling system, the higher the water temperature before it boils.
Typical operating temperature of the cooling system in the 3800 is around 180-230 F, the preferred temperature is around 200-215 F. Anything over 230 would be considered hot, but as long as
pressure and coolant have not been lost due to hose rupture hose or other scenario, it's not overheated. Loosing pressure and coolant at temperature are what can cause damage.
On one occasion I have reached 240 F in my car, I was trapped in stopped traffic on I77 in Charlotte NC. It was a HOT afternoon day. The coolant temp went down when traffic finally started moving again, the car handled it with no problems.
If your really worried about a blown head gasket, watch for water in the oil, and/or get the coolant checked for combustion gases.
