@Danja, I am not certain. I know when I pulled the old thermostat it was covered in sediment. Yuch I am going to boil it if I remember this afternoon and see if it opens. Also, my slim fans are bolted in the stock location, which is about 3/4-1"off of the radiators. I think for more effective cooling I am better off putting them on the rad and using slim fan straps for faster cooldown. Fans do not come on @highway speed right? I suspect air.