Because the engine is not reaching normal temperature, check whether the thermostat is stuck open or missing and replace it if needed. A clogged heater core is less likely until the engine runs at the proper temperature.
The owner reports that the Ford heater blows air but never gets truly hot and the temperature gauge stays on cold, asking whether the heater core or thermostat is at fault. The expert says a clogged heater core is a common heat problem, but here the lack of proper operating temperature points to a thermostat stuck open or removed. A second owner describes similar heat and gauge issues on a 1982 150, but no further diagnosis is given.
