Bought the truck about 8 months ago. Had a problem overheating then. I changed water pump, thermostat, clutch fan... turned out to be the radiator which supposably new. Issue fixed. 2 weeks ago during the "Polar Vortex" I believe there wasn't enough coolant in it and overheated again. I have a Failsafe thermostat and after refilling the coolant it stopped overheating but only blew cold air. Failsafe stayed open. Replace the thermostat today with another failsafe, but now it is overheating again. Both hoses to and from the heater core are hot but the top hose to the radiator is cold. Could the new radiator I bought 8 months ago be clogged?

 

Failsafe thermostat or not. The thermostat must not be opening. Only other possibility, you are SLIGHTLY low on coolant.

 

Also make sure the thermostat is not installed backwards. The Thermal Spring faces towards the Engine.

I have had 2 customers in the last week with overheating problems, related to thermostats being installed backwards!

 

Not trying to give you a hard time, but a 92 doesn't have a V-6.

Replace the thermostat with an OEM Motorcraft.

 

You may want to do a co2 test to see if co2 is present in your cooling system. I hate to say it but looking more to a head gasket problem. Your t-stat will not open because of a blown head gasket. Your t-stat only opends with water temp. If you have an air pocket because of compression going into the cooling system it will not open. It cannot detect air temp only fluid temp. So have a test co2 done.