My mech replaced the thermostat and its pretty much taking care of the problem.
With the temp @ 45 today...he changed the thermostat let the car idle for 1 hr with no problem...hovered just above the 80 hash mark the entire time.
When I picked up the car...went for a 20min drive of 70-80mph no problem. Ran with full A/C and also full heat...no problem...temp remained just a a little above 80. Came home let it sit for 15mins still I couldn't get the temp to rise to 85 or 90.
My mech said...drive around for a week...if its acting up then we'll try something else...hopefully this will be the only problem.
Talked with him for a bit afterwards.....said most of the time he's only found thermostats going bad. If it was ever a radiator problem its was from the older design like on the 300E that didn't have the metal neck. With all the difference in temp the neck would become brittle over time and crack.
Another happy E320 owner again :-)