yo,
Could be a number of issues as the guys mentioned above;
From Radiator, see my site @
http://www.broncolinks.com/index.php?index=188
t stat, see my site @
http://www.broncolinks.com/index.php?index=189
to hoses, see my site
http://www.broncolinks.com/index.php?index=187
heater core issues;
such as:debris in Blower Motors/Ducts see my site @
http://www.broncolinks.com/index.php?index=495 for such as:
Location in 80-96 Blower Motors/Ducts
This shows where leaves build up in '80-96 truck ductwork. If they build up around the resistors (green),
the entire truck can catch fire if the motor (yellow) is NOT at full speed all the time.
See more diagrams there and info
Source: by Steve83 (Steve, That dirty old truck) at
http://www.supermotors.net/clubs/superford/vehicles/registry/media/71652
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See my site @
http://www.broncolinks.com/index.php?index=86 for HOT LINKS to such Info as:
Heater Core Failure, Repeated TSB 01-15-06 for 85-96
Lack of Heat, Temperature Blend Door Cam Spring Does Not Blend Door to Seat Properly TSB 92-4-13 for Vehicles Built Prior to 11/11/91, 92 Bronco & F Series & F-47
Low or No Heat/Air Conditioning, High Effort to Turn Temperature Control Knob, Poor Temperature Modulation TSB 96-13-7 for 92-95 Bronco, F Series, F-47
Low/No Heat When Temperature Knob Is Set At Full Heat TSB 94-20-16 for 92-94 Bronco & F-150-350 Series
Odors, Eliminate Air Conditioning Musty & Mildew Type TSB 98-2-7 for 92-96 Bronco; 92-97 Aerostar, Econoline, Explorer, F SUPER DUTY, F-150, F-250 HD, F-250 LD, F-350, Ranger & many others
Poor Heater/Defroster Performance in Engine Coolant Concerns TSB 93-24-08 for 84-94 Bronco, F Series, Aerostar, Econoline & many others; Blend door operation, Check blend door for binding and proper operation; Mode door operation. Check mode door for binding and proper operation. Blower fan operation, Check blower fan for proper operation and control. Heater core plugged, Flush cooling system. Coolant level, Check level in radiator and coolant recovery reservoir. Leakage, Check for leaks using pressure test. Thermostat operation, Check Thermostat. Refer to "Thermostat Diagnosis" procedure.
"...The heater hose connected to the intake manifold or t-stat outlet flows AWAY from the engine. The heater hose connected to the water pump flows TO the pump... In most engines, coolant ALWAYS flows thru the heater core circuit. The outlet for the heater core is beside the t'stat, so the t'stat can never restrict flow to the heater core. This serves 2 purposes: it allows an unrestricted failsafe coolant flow (although the heater core isn't nearly large enough to cool the engine if the radiator becomes restricted), and it allows the cabin to receive heat as soon as it becomes available, irrelevant of the radiator temperature, ambient temp, t'stat, fan, or clutch/relay. Even if the coolant level becomes critically low, the heater circuit will still generally have coolant in it since it takes less coolant to sustain flow within its smaller capacity. In some vehicles, a problem has been recognized in which high engine RPM during warmup can result in excessive pressure within the heater core, resulting in rupture. The fix is to retrofit a slight restriction (an orifice plate) into the circuit upstream of the heater core to limit the flow, and thereby, the pressure. Returning coolant is typically routed directly into the water pump. If the heater core fails, it is safe to loop a hose from the outlet directly back to the return indefinitely. It may also be beneficial to occasionally reverse the hoses at the heater core to keep it flushed out. The direction of flow in the heater core is irrelevant..."
Source: by Steve83 (Steve, That dirty old truck) at fourdoorbronco.com
