TSB 92-15-14 Fan Clutch Diagnosis
Publication Date: JULY 15, 1992
LIGHT TRUCK: 1987-92 BRONCO, ECONOLINE, F-150-350 SERIES
1988-92 F SUPER DUTY
ISSUE: A comprehensive diagnostic procedure has been developed for determining if the engine cooling fan clutch is functioning properly. A fan clutch that is not functioning properly may cause engine cooling concerns and/or vibration.
ACTION: Use the following diagnostic procedure to determine if the fan clutch is functioning properly. A fan clutch that is not functioning properly should be replaced.
CAUTION: DO NOT ATTEMPT TO MODIFY THE BI-METALLIC COIL ON THE FACE OF THE FAN CLUTCH.
DIAGNOSTIC PROCEDURE
NOTE: PROCEED ONLY AFTER COMPLETING THE ENGINE COOLING DIAGNOSIS PROCEDURE IN SECTION 03-03 AND THE ACCESSORY DRIVE BELT TENSION PROCEDURE IN SECTION 03-05 OF THE APPROPRIATE SERVICE MANUAL.
1. Turn off the air conditioner, heater-A/C fan and radio.
2. Check for viscous drag...
a. Before starting the engine, rotate the fan and clutch assembly by hand. It should have some viscous drag, but it should turn smoothly during the full 360%uFFFD of rotation.
b. Replace the fan clutch if it does not turn smoothly or does not turn at all. Refer to the Dealer Master Parts Catalog for correct parts usage. Refer to the appropriate Service Manual, Section 03-05, for service details.
c. Replace the fan if there are only cracks.
d. If this is not the concern, go to Step 3.
3. Check for lack of viscous drag...
a. If the fan clutch spins with no viscous drag when it is cold, and it has not been run for an hour or more, it should be replaced. Refer to the Dealer Master Parts Catalog for correct parts usage. Refer to the appropriate Service Manual, Section 03-05, for service details.
b. If this is not the concern, go to Step 4.
4. Check for excessive fan clutch bearing clearance (cold fan clutch)...
a. Hold the tip of the fan blade between the thumb and forefinger.
b. Lightly pull toward the radiator, then push toward the engine.
c. Repeat the motion several times.
* The total rocking movement at the end of the fan blade should be 2/10" (5.1mm) or less when no more than eight ounces of force is applied.
* A force greater than eight ounces may deflect the fan blade with erroneous results.
d. Replace the fan clutch if more than 2/10" (5.1mm) of movement is observed. Refer to the Dealer Master Parts Catalog for correct parts usage. Refer to the appropriate Service Manual, Section 03-05, for service details.
e. If this is not the concern, go to Step 5.
5. Install a temporary engine tachometer if the vehicle is not equipped with a tachometer.
NOTE: DURING THE FOLLOWING TESTS, BE SURE TO MONITOR THE ENGINE COOLANT TEMPERATURE BY THE TEMPERATURE GAUGE IN THE INSTRUMENT CLUSTER. SHUT OFF THE ENGINE IF THE TEMPERATURE RISES ABOVE THE MAXIMUM RECOMMENDED LIMIT FOR THE ENGINE OR IF COOLANT IS DISCHARGED OUTSIDE THE SYSTEM. THE TESTS CAN BE RESUMED USING THE FOLLOWING PROCEDURES AFTER THE COOLANT TEMPERATURE DROPS TO A NORMAL OPERATING LEVEL.
NOTE: IF THE HOOD IS LEFT OPEN, THE FAN NOISE MAY BE EASIER TO HEAR.
WARNING: DO NOT STAND IN LINE WITH THE FAN.
6. Start the engine.
7. Check for fan disengagement and be aware of the following operational characteristics.
* The fan clutch may be engaged when the engine is first started. This will be apparent from the noise level of the fan which has a distinctive roar.
* The fan clutch engagement is due to the viscous silicone fluid draining back and filling the gap between input and output components.
* Running the engine at a constant speed of about 2000 rpm should pump the fluid back to its reservoir, disengaging the fan clutch after no more than five minutes.
* As the fan speed declines, the noise will drop off to a level inaudible to most observers.
a. Continuing the test, If the fan clutch does not reengage after five more minutes at 2000 rpm, the fan clutch should be replaced. Refer to the Dealer Master Parts Catalog for correct parts usage. Refer to the appropriate Service Manual, Section 03-05, for service details.
b. Repeat the test procedure after fan clutch replacement to confirm the fix and to assure customer satisfaction.
c. If this is not the concern, go to Step 8.
8. Stop the engine.
Cut and install a piece of cardboard large enough to cover the front of the radiator with a six inch diameter hole in line with the fan clutch.
If it is not possible to install the cardboard directly against the radiator, attach it to the A/C condenser.
9. Start the engine.
a. With the gas engine at 2700 to 3000 rpm or diesel engine at 2100 to 2300 rpm, the vehicle temperature gauge will rise steadily as the engine warms and then appear to level off for a short time when the thermostat opens.
b. Make note of the temperature gauge position when the thermostat opens. The engine coolant temperature will continue to rise until the fan clutch engages.
10. Check for fan engagement...
a. Continue to observe the coolant temperature gauge. As the fan clutch engages, the fan noise will continue to increase and then level off at full engagement. The fan clutch may cycle off-and-on a few times during the initial engagement.
b. If the fan clutch does not engage before the maximum indicated safe operating engine coolant temperature is reached, it should be replaced. Refer to the Dealer Master Parts Catalog for correct parts usage. Refer to the appropriate Service Manual, Section 03-05, for service details.
c. Repeat the test procedure after fan clutch replacement to verify the fix and to assure customer satisfaction. The rate of rise of the coolant temperature will slow down after clutch engagement, but it will continue to rise as long as the radiator remains covered.
d. If this is not the concern, go to Step 11.
11. Check for fan disengagement...
a. After completion of the above tests, shut off the engine.
b. Remove the cardboard cover from the front of the radiator.
c. Restart and return the gas engine to 2700 to 3000 rpm or diesel engine at 2100 to 2300 rpm, continuing to watch the coolant temperature which will begin to decrease. The fan rpm will drop to a reduced noise level where it was before the cycle began which indicates that the fan clutch has disengaged.
d. If the fan clutch remains engaged and the coolant temperature has dropped below the thermostat opening temperature (as noted in Step 9) for at least five minutes, the fan clutch should be replaced. Refer to the Dealer Master Parts Catalog for correct parts usage. Refer to the appropriate Service Manual, Section 03-05, for service details.
e. Repeat the test procedure after fan clutch replacement to confirm the fix and to assure customer satisfaction.
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS:
Eligible Under Bumper To Bumper Warranty Coverage For 1992 Models, Basic Warranty Coverage For All Other Models
OPERATION DESCRIPTION TIME
921514A Diagnosis Only - F-Series And Bronco 0.6 Hr.
921514B Diagnosis Only - 1987-1991 Econoline 0.9 Hr.
921514C Diagnosis Only - 1992 Econoline 0.8 Hr.
921514D Inspection And Replacement Of Fan Clutch - 1987-92 F-Series And Bronco Except 7.3L Diesel 0.6 Hr.
921514E Inspection And Replacement Of Fan Clutch - 1987-92 F-Series With 7.3L Diesel 0.8 Hr.
921514F Inspection And Replacement Of Fan Clutch - 1987-91 Econoline Except 7.3L Diesel 0.8 Hr.
921514G Inspection And Replacement Of Fan Clutch - 1987-91 Econoline With 7.3L Diesel 0.7 Hr.
921514H Inspection And Replacement Of Fan Clutch - 1992 Econoline Except 7.3L Diesel 0.6 Hr.
921514I Inspection And Replacement Of Fan Clutch - 1992 Econoline With 7.3L Diesel 0.8 Hr.
921514J Complete Diagnosis And Replacement Of Fan Clutch - F-Series Except 7.3L Diesel 0.9 Hr.
921514K Complete Diagnosis And Replacement Of Fan Clutch - 1987-1992 F-Series With 7.3L Diesel 1.1 Hr.
921514L Complete Diagnosis And Replacement Of Fan Clutch - 1987-1991 Econoline Except 7.3L Diesel 1.4 Hr.
921514M Complete Diagnosis And Replacement Of Fan Clutch - 1987-1991 Econoline With 7.3L Diesel 1.3 Hr.
921514N Complete Diagnosis And Replacement Of Fan Clutch - 1992 Econoline Except 7.3L Diesel 1.1 Hr.
921514O Complete Diagnosis And Replacement Of Fan Clutch - 1992 Econoline With 7.3L Diesel 1.3 Hr.
See also:
A Complete Explanation of the Engine Cooling System
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7.3L Engine Fan Clutch Test Specifications:
WP pulley ratio: 1.1
Engine test RPM: 3000
Min.Fan RPM at disengage temp: 650 @ 122%uFFFDF
Min.Fan RPM at engage temp: 2900 @ 200%uFFFDF
WP test RPM: 3300
Minimum Fan Clutch Requirement Test -- Cold
1. WARNING: TO AVOID THE POSSIBILITY OF PERSONAL INJURY OR DAMAGE TO THE VEHICLE, DO NOT OPERATE THE ENGINE UNTIL THE FAN HAS BEEN FIRST EXAMINED FOR POSSIBLE CRACKS AND SEPARATION. Using a suitable marker, mark the water pump pulley (8509), one of the fan blade retaining bolts and the crankshaft pulley (6312).
2. Connect a tachometer to the engine.
3. Install a throttle adjusting tool.
4. Connect a Sun Strobe Light or equivalent. This can be an SLT-1 or SLT-2 Strobotach or an STA-1 Strobe Trigger adapter for the Sun Distributor Test Stand. A Digital Photoelectric Tachometer 055-00108 or equivalent may also be used for this test.
5. Start the engine and run it at approximately 1500 rpm until engine temperature has normalized.
6. Adjust the engine to the testing speed in the Specifications above.
7. Operate the strobe light at water pump test speed and aim it at the water pump pulley. Adjust the engine speed until the light flashes and the water pump pulley marks are synchronized.
8. Aim the timing light at the fan retaining bolts. Adjust the strobe light until it is synchronized with the marked fan retaining bolt (fan appears to stand still).
9. The fan speed must not be greater than the specified fan test speed at water pump test speed.
10. Turn the engine OFF.
11. If the fan speed was greater than the specified fan test speed, check for proper parts usage. If the correct parts are used, replace the fan clutch (8A616). If the part(s) are not the correct ones, replace the part(s) and perform the test again.
12. If the engaged fan clutch requirement test is going to be performed, do not remove the tachometer, strobe light or throttle adjusting tool.
13. If a Maximum Speed Fan Clutch Requirement test is not going to be performed, remove the tachometer, strobe light and throttle adjusting tool.
Maximum Speed Fan Clutch Requirement Test
1. WARNING: TO AVOID THE POSSIBILITY OF PERSONAL INJURY OR DAMAGE TO THE VEHICLE, DO NOT OPERATE THE ENGINE WITH THE HOOD OPEN UNTIL THE FAN HAS BEEN FIRST EXAMINED FOR POSSIBLE CRACKS AND SEPARATION. If the disengaged fan clutch requirement test was not performed, follow Steps 1 through 5 under Minimum Speed Fan Clutch Requirement test.
2. Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille (8200), this will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.
3. Place the air conditioning selector, if so equipped, in the maximum position and the blower switch in the high position.
4. Adjust the strobe light to water pump test speed.
5. Start the engine and adjust it until the water pump pulley is synchronized with the strobe light. This will be near the engine testing speed given in Specifications.
6. Synchronize the timing light with the fan to fan clutch retaining bolt.
7. The fan speed must meet or exceed the specified minimum fan blade test speed at water pump test speed.
8. If the fan speed was less than the specified fan test speed, replace the fan clutch.
