I found out a couple months ago I head a blown head gasket. The temp gauge never showed signs of overheating. At that time I checked the hoses and the upper hose was hot & the lower was cold when engine at “operating” temp. I thought well thermostat went bad. I replaced head gaskets, water pump, thermostat. I have just come across the same initial situation of the upper hose is hot, lower hose is cold, temp gauge did not show over heating. Both heater core hoses are hot & I have heat. Has anyone ever come across this or ha e an idea of what would cause it.