Detroit Diesel 4000 Series, Service Manual, Page: 2641 / 2706

SERIES 4000 12/16V SERVICE MANUAL
3. Solenoid valve may not be working properly.
Install a pressure gage in the "COM" or "CLUTCH" port. With a cool engine the solenoid
valve should supply "0" oil pressure to the fan clutch, and the fan should free-wheel.
If the pressure gage readings are correct, disconnect the oil supply hose from the fan
clutch "OIL IN" port. The clutch should release fully, and the fan should free-wheel.
Go to step 4 for a further probable cause.
4. Fan mounting bolts may be too long.
If the fan mounting bolts extend through the fan mounting hub and contact the front of the
front bearing retainer, the fan clutch may be mechanically locked up. Replace with bolts
that fit full thread in fan mounting hub, but do not extend too far through. (Check to insure
bearings in fan clutch have not been damaged.) Go to step 5 for a further probable cause.
NOTE:
SAE grade 8 bolts are recommended in mounting the fan to the fan mounting hub. If
washers are used, they, too, should be hardened. Bolts holding the fan on the fan
mounting hub must fully engage the threads, but must not extend too far through the fan
mounting hub to contact the front of the bearing retainer or other components.
5. A manual override switch may be preventing the fan clutch from releasing.
(Although not recommended by Rockford Powertrain, some vehicles are equipped with a
manual override switch in the cab which overrides the control of the thermal sensor.) Turn
switch to "Off" or replace a defective switch. Go to step 6 for a further probable cause.
6. Control pressure line is restricted, not allowing oil to exhaust from clutch.
Relieve restriction. Go to step 7 for a further probable cause.
7. Compressor override system may not be operating properly.
If vehicle is equipped with air conditioning and override, check components of the system
to ensure false signal is not being sent to solenoid, causing fan clutch lockup.
All information subject to change without notice.
Copyright © DETROIT DIESEL CORPORATION
E -11