My 66 coupe with 289 4v 4 speed overheated a while ago due to leaking water pump and broken hoses. I replaced water pump, all radiator and heater hoses, thermostat , thermostat housing, radiator and changed to electric fan. Was driving great then randomly overheated again, no signs of a leak anywhere. No air bubbles as i checked for that. Any ideas what I should look at or try next?