Are you putting it in facing the right way, o-ring & everything? It should just set right in place, with the spring inside the cylinder head. If it is staying that cold (which mine used to when the t-stat dies & stayed open), it is either the t-stat, or there is somewhere else that a LOT of coolant is bypassing the t-stat. Is the housing damaged inside at all? There should be a little groove between the inlet & outlet side of the housing, make sure it is cleared of gunk. Also check inside the head where the t-stat site to make sure that there is not some sort of damage allowing the coolant to flow by the t-stat.