[masterbeavis]

Did you use RTV to seal the t-stat housing in any way? If so, take the housing off and redo it minus the RTV. I have personally had a Tstat get stuck closed because we used too much RTV on the stat housing. (we used very little to begin with). The RTV squished out, eventually broke off partially, and got stuck in the tstat... RTV used elsewhere in the cooling system can and will cause the same problem. While you have the t-stat out, toss it and buy a balanced one, they fail in the open position (except RTV related issues, and are less prone to failing like the cheapies do. Robershaw used to be the brand to buy, now Prestone sells them (you see the robertshaw name on the package.