Hi John.
My name is Javier, and I recently got a 550, 2000. I was reading an old post about your 550 running on the hot side of the temp gauge. Mine happens to be doing the same, and I just changed the water pump, as well as the thermostat, and still is doing the same. I wonder if you had the radiator replaced for that, since the mechanic said that it was the last part to replace pertaining that matter.
I will really appreciate your insight in this matter.