I just rebuilt a 65 289 when it gets hot the thermostat will not open and the thermostat hose is really hard (from compression?) however, no water is flowing back through. The water pump sucks the water out of the radiator but it's not flowing back through. I changed the thermostat and still get the same results. I took the thermostat out and of course it circulates fine. The water pump is new and pumps from the passenger side (just info) Could the return hose on the water pump not be working since water should pass through it when the thermostat is closed. I blew into the return hose and felt no restriction, the thermostat is installed correctly. I bought another thermostat and tested it in how water and it opened I'll try that one tomorrow. Any suggestions would be greatly appreciated.
Thanks

 

the only thing that will make the upper radiator hose hard before coolant flow & full temp is combustion gases interring the coolant system.aka blown head gasket wrong gasket warped or damaged heads or block & of course cracked block or head when you say passenger side assume that is the lower radiator hose .
are you completely full of coolant the t stat needs to be in full contact with a liquid or won`t work properly.
coolant does not pass the thermostat when it is closed the is its sole purpose to regulate coolant flow to maintain the temp marked on it in the engine.
so if the thermo end of the T stat is facing the block & you engine is going above the T stat rated temp bad T stat .
I think you have a more serious problem that a thermostat.
keep us informed.
Paul

 

I drill 1/16 inch hole in all my tstats to allow easy filling and steam bubbles to exscape the intake...some brand come with hole....

 

I think the block is cracked I took the engine out and tore it apart, the machine shop now has it, I should know something in a few days.