All winter I have been plagued with the heater in my 40cyl 86 Ranger blowing hot and cold intermittently. Mostly blowing cold. I replaced the thermostat, swapped hoses, checked the air door and heater core all to no avail. As a last gasp, i installed a new coolant recovery system ($7.99 @ Schucks) filled the radiator to the top and purged the coolant overflow line so only coolant was in it. Problem gone. Apparently the failed coolant recovery system (leaking reservoir) was the cause, causing "air-lock" in the heater.

-jwk-

Oregon