If it's a stock motor then use whatever came in it for the Thermostat. I think it's 180. I am having problems with my truck running too rich right now and not starting very easily. One prob is that the Q Jet carb is old and needs rebuilt but then again there are millions of hoses and some aren't even hooked up and I can't find where they even go. I looked for places where hoses can go into and nothing to be found. I am going to keep up with this thread and see what you come up with because I have kind of the same problems.