The head gasket for a 261 had been installed purposefully to restrict coolant flow through the block. In cold climates you need it to run warmer as the cold air will keep it cool whereas in Houston- quite a hot climate- you need the maximum coolant running through. The 235 gasket was placed and she has run cool ever since.
That's a load of bunk. Whoever put the WRONG gasket in your 235 just screwed up.
The thermostat is what regulates temperature, not putting an incorrect head gasket in place that blocks some of the coolant passages.
True story.
