If the radiator fans are not running resulting in overheating, the first thing to check are the two fuses:
Radiator Cooling Fan Fuse 1 #28 30A
Radiator Cooling Fan Fuse 2 #29 30A
If the fuses are OK, the other items in the diagnostic chain
1 Connectors & wiring. Check for cuts and corrosion
2. Fan final stage amplifier that is located on the passenger side under-hood ahead of the radiator (black finned module). If you have access to a known good unit, swap it out and see if the fans run.
3. Fan controller (located to the right of the passenger seat under the carpet covered panel).
4. Fan motors
Not directly an issue, but also to be aware is the cooling flaps. 928 S4s had a shutter system in front of the radiator. By now, many may be disabled in the open setting. If fuse #23 is removed, that is likely why.
Cooling Air Flap Adjustment Fuse #23 7.5A
Cooling Air Flap System Relay XVII
Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
