Just bought a 01 Bonneville with 209000 miles runs good but my oil pressure gauge goes max when I start the car going to replace oil pressure sensor ,filter and oil wondering what oil to use

They recommend 5w30 weight oil, witch I like running in the cold weather, in the heat I like 10w30 weight. Also keep with the dex coolant. That is what it came from the factory.

Better to read high than low. I agree with Js08016, if it drops back to normal after the engine gets up to temp - leave it be. Good idea to drain and change oil and see what happens to it with proper viscosity and fill level.

Have a 2000 SSEi with 199k. Have used Mobile1 synthetic since day one. 5w30 year round. Engine is like new, inside. Never too late to start, eh?

10-30 is best and it is normal to have various oil pressure readings as the car is either cold, hot, idling or revving motor. 30 to 55 is normal depending on what the motor is doing. Enjoy and drive the car.