I am starting to wonder if my temp sender is incorrect.  What size are the temp sender threads in the rear of the drivers side head?  1/8" NPT?
What about the threads in the thermostat housing?

Thanks.  

1954-1956 Ford Y temperature sending unit threads are 3/8” NPT.  1957 and newer is ¼” NPT.  The heater hose connection in the intake manifold behind the thermostat is 3/8” NPT for all years.

Lorena, Texas (South of Waco)

Thanks Ted!