X2 on the 195...
Arb, have you used the prestone flush to get oil out of the cooling system?? I tried it years back and it didn't work so well.. Laundry soap such as tide is usually what I've been using to degrease.. Not as harsh as say cascade, but still a decent non foaming degreaser...
The thermostat will dictate the coolest temperature the engine will run. Get a thermostat with the proper temperature, and the coolant is a safety measure to keep it from getting much hotter than that, like during extended "spirited" driving.
The engine will run below thermostat temps; the thermostat really just controls when you gain access to the radiator.
If you have a coolant issue or combustion issue and your engine is running well below t-stat temp (say, only firing on two cylinders, perhaps, or severely underfueling) then the thermostat won't have any bearing on engine temperature.
Does anyone know where to get a Wahler or Behr thermostat in southern california, and I mean from a autoparts place other than the stealership?