I recently changed my t-stat, OEM in '04 was 150* stat. I used Indian Head Permatex gasket Shellac on the stat to housing sealing surface and then put in a new o-ring which probably also got some of the excess shellac on it which I figured would hold it in there better too.
I saw the permatex aviation sealer at the parts store but there were several kinds and I wasn't sure so I just went with the shellac since it is safer (no solvent fumes) and has worked for me for years on other applications. I also replaced the t-stat gasket and as Lou said, I bought several...a 2-pack of Sierra (with the gold brads) and a single OEM Volvo gasket. I went ahead and tried the sierra this time around and shellac'd it to the housing but DID NOT put any shellac on the intake manifold flange because I figured I did a good enough job of cleaning the sealing surface. However, upon a test run on the trailer, the gasket was sweating a tad bit until it warmed up..The Volvo gasket is more well made so I suspect it would have been fine to use without shellac. But the Volvo gasket has a smaller inside diameter and covered part of the intake manifold flange opening and I'm dealing with rust in the system so I wanted the best possible flow which is why I used the sierra gaskets which did not even cover the entire flange at all.
May I ask - how were you determining the temp for the numbers you gave? Did you use gauge only or IR? ALSO - what is the half-way point on your gauge? Mine is 120-220 so I "assume" the half-way is 170*?
