I cured my overheating problems in my 81 Sd with the drilling 1/8 inch whole in the thermostat method the I found in the search section (I think I typed in "drill thermostate" direction very clear complete with drawings, car is running a steady 85 no matter what outside tempiture is.
William Rogers.......
74 240D
81 Sd
81 2wd 454 Blazer hot rod