Hello, I have a 1981 F150 4x4 with straight 6 and carb. I recently had to replace my radiator had a small accident the rad was destroyed along with the fan, So I have replaced the rad, fan, bottom hose line and both heater core lines. Now the old rad had the orange coolant in it, and with the freezing weather my hose is frozen so I did not flush the system before putting new parts on and bleeding the system with the green coolant. Since then i have noticed that the truck starts up and warms up fine both rad hoses are warm, heat works and when i start driving i notice the heat goes completely cold, I stop look under hood and it appears as tho the over flow hose shot out coolant and notice some steam coming out of it. Now is this due to me not flushing the system out and starting fresh, because i dont believe its the head gasket cause there is no lose of power oil is fine and it still drives normal just. Also this didn't start until after the accident and i put the new parts on before it was never a problem. Possibly heater core issue? What you guys think?

 

Being an orange coolant, it sounds like somebody put GM's DEXCOOL in the cooling system. I would have done a complete flush of the cooling system before installing new green antifreeze. DEXCOOL has been known to gel up when other types of coolant are added to it. When DEXCOOL gells, you do not get proper cooling thruout the engine.