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FORD BRONCO -> ENGINE & COOLING; swaps, specs, snorkels, vac. diagrams... -> ENGINE COOLING -> Thermostat
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Description & Operation, Diagnosis & Testing, Removal & Installation, Service Procedures, Cleaning & Inspection & Special Service Tools/Equipment in a 96 from 1996 F-150, F-250, F-350, and Bronco Workshop Manual
Source: by Ford via
DTC P0125 Insufficient Coolant Temperature For Closed Loop Fuel Control "...Indicates the ECT or CHT sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting engine. Insufficient warm up time; Insufficient warm up time Low engine coolant level Leaking or stuck open thermostat Malfunctioning ECT sensor..." miesk5 Note; Remember to have engine @ Normal Operating Temperature before doing the KOER portion
Source: by slingblade at The National Lightning Owners Club
Engine Coolant Concerns TSB 93-24-08 for 84-94 Bronco, F Series, Aerostar, Econoline & many others; in Table, check Thermostat; "...ISSUE: Engine performance concerns such as hesitation or stall, rough idle, and/or poor fuel economy may be caused by the thermostat stuck in an open position or opening at a temperature lower than specified. ACTION: Use the following "Cooling System Diagnosis" procedure to diagnose a cooling system that may not be reaching normal operating temperature. Follow the "Thermostat Diagnosis" procedure to determine if the thermostat may be at fault. Check the thermostat without removing it from the vehicle by using Rotunda Service Coolant Temperature Monitor Harness 007-00064. DIAGNOSIS PROCEDURE; A new cooling system diagnosis procedure has been developed for engines that do not reach normal operating temperature. A new thermostat diagnosis procedure also has been developed, using a new service coolant temperature monitor harness. See chart for proper diagnostic procedure. NOTE: THIS PROCEDURE WILL DIAGNOSE ONLY COOLING SYSTEMS THAT MAY NOT BE REACHING NORMAL OPERATING TEMPERATURE. IT WILL NOT DIAGNOSE A THERMOSTAT THAT CAUSES AN ENGINE OVERHEAT CONDITION. THERMOSTAT DIAGNOSIS; NOTE: DISCONNECTING THE POWERTRAIN CONTROL MODULE (PCM) TO ATTACH A BREAKOUT BOX OR AN EEC IV MONITOR WILL ERASE THE ADAPTIVE LEARNING FROM MEMORY AND MAY "HIDE" A DRIVE CONCERN TEMPORARILY UNTIL THE ADAPTIVE LEARNING IS RE-LEARNED. NOTE: THIS PROCEDURE IS MOST ACCURATE IF PERFORMED INDOORS AT LESS THAN 100°F (38°C) AMBIENT TEMPERATURE. THIS TEST MAY BE PERFORMED WITH OR WITHOUT THE HOOD OPEN AND WITH THE ENGINE WARM OR COLD. CAUTION: ALWAYS VENT THE EXHAUST TO THE OUTSIDE WHEN PERFORMING THIS TEST. 1. Check the coolant level in the radiator and coolant recovery reservoir. 2. With the key in the "off" position, proceed as follows: a. Remove the engine coolant temperature (ECT) sensor harness connector. b. Attach Rotunda Service Coolant Temperature Monitor Harness 007-00064 as a jumper between the PCM and the ECT. c. Attach Rotunda 73 Digital Multimeter 105-00051 or equivalent to the thermostat monitor harness. Voltage values (0-5vdc) may now be monitored while the sensor retains its connection to the wiring harness. NOTE: A ROTUNDA NEW GENERATION STAR TESTER (NGS) 007-00500 OR THE ROTUNDA SERVICE BAY DIAGNOSTIC SYSTEM (SBDS) 001-00001 MAY BE USED TO MONITOR THE ECT ON VEHICLES EQUIPPED WITH DATA COMMUNICATIONS LINK (DCL). THE SBDS SEQUENCE TO USE FOR THE SCREEN IS "TOOLBOX - ELECTRONIC ENGINE CONTROL AND DCL - ITEM". 3. Vehicles equipped with electric engine cooling fan(s) must have a fan running during this test (high or low speed may be used). Two methods may be used to turn the fan(s) on: a. Disconnect the A/C compressor clutch power supply and turn the climate control to A/C "ON". Or b. Disconnect the power supply to the cooling fan and supply 12 volts direct to the fan connector from the battery. NOTE: A GROUND MAY BE REQUIRED FOR SOME APPLICATIONS. 4. Place transmission in "park" or "neutral". NOTE: RUNNING THIS TEST WITH THE VEHICLE IN GEAR OR WITH THE A/C COMPRESSOR CLUTCH ENGAGED (RUNNING) WILL CAUSE IMPROPER DIAGNOSIS 5. Start the engine and allow to idle throughout this test: a. Allow engine to run for 2 minutes, then record ECT voltage. b. From now on, record ECT voltage every 60 seconds. c. When the ECT voltage trend changes direction or changes only slightly (0.03 volts or less) from the previous reading, record this as the thermostat opening voltage. d. Use the "Voltage and Corresponding Temperature Chart" shown below to obtain actual coolant temperatures. 6. If the opening voltage is GREATER than 0.75 volts (less than 180° F/ 82° C), or 0.85 volts (170° F/ 77° C) for 2.3L HSC engine only, replace the thermostat. Refer to the dealer Master Parts Catalog for correct thermostat usage. 7. If the thermostat opening voltage is LESS than 0.75 volts (greater than 180° F/ 82° C), or 0.85 volts (170° F/ 77° C) for 2.3L HSC engine only, the thermostat is good and should NOT be replaced. The "Cooling System Diagnosis Chart" should be referenced for further instructions. NOTE: The 10° F opening temperature difference for the 2.3L HSC engine is due to the ECT sensor location. OTHER APPLICABLE ARTICLES: NONE SUPERSEDES: 93-14-04 WARRANTY STATUS: INFORMATION ONLY..."
Source: by Ford via Steve83 (Steve, That dirty old truck) at
Faulty Thermostat or Coolant Sensor; Emissions Failures, Diagnosis Tech Tips (high CO, O, CO2, etc.)
Source: by via
Heater Outlet Nipple Fabrication (from the t'stat cover to the heater core) in an 83
Source: by Steve83 (Steve, That dirty old truck) at
High Idle & Dieseling Troubleshooting Chart in a 94, from PCED Chart 7 for a 94; Preliminary Checks; Overheating or not Reaching Normal Operating Temperature, Vacuum Leaks, Throttle Plate & Linkage, Speed Control Chain Binding/Sticking, Air Intake Tube/ Intake Manifold Leaks..." READ MORE
Source: by Ford via Steve83 (Steve, That dirty old truck) at
Installation pics in a 92 5.8
Source: by 2bet at
Location Pic in 87-95 4.9
Source: by Steve83 (Steve, That dirty old truck) at
Source: by Steve83 (Steve, That dirty old truck) at
Repair Price Estimator, Bronco from 90-96 and other Fords; including labor & parts, shops in area, by Zip Code
Source: by RepairPal
Source: by Kyle W at
Replacement Discussion
Source: by members at FSB
Replacement in a 92 5.8
Source: by digitalbill (Bill Crozier) at
Replacement in a 93
Source: by Kevin L at via
Replacement in a 94 5.0 (part of his gauge installation)
Source: by Aaron42 at FSB
Stant 205 Degree, housing & by-pass hose pics
Source: by Sixlitre (Malcolm H, Eddie Bauer) at
Thermostat w/Pressures & Gasket Parts Catalog, Bronco/Ford truck & all Fords w/Ford Part Numbers & Cross References; 29.35 MB PDF
Source: by