Magnum water neck and thermostat ?'s

I have that same thermostat housing, and I just had it off the other day, and thought to myself, that t-stat sure does fit really loose in there. I wonder if I just threw the old t-stat on that I had, and what I really need to do is pick up the right t-stat now. It does fit, but I could see water being able to get around it when closed.