The MGB GT V8 was fitted with twin electric cooling fans from the start of production, a significant departure from the four-cylinder MGB's single engine-driven mechanical fan. The fans are mounted on brackets in front of the cross-flow radiator and blow cold air through the matrix when activated, rather than drawing air through it as on a conventional puller-fan installation. There is no provision for an engine-driven fan on the V8: all radiator airflow at low road speeds depends on the electric fans operating correctly. The twin-fan installation also provides a degree of redundancy, should one fan fail, the other can keep the engine within tolerable temperature limits in most conditions.
Fan Motors and Blades
Each fan comprises a small electric motor with a multi-blade plastic fan blade. Motors are conventional brushed DC units running directly from the car's 12-volt supply when switched on. Worn motor brushes, dry bearings and corroded earth connections all cause symptoms ranging from slow fan speed to complete failure.
Replacement motors and blades are available individually.
'Otter' Thermo-Switch
The fan is controlled by the BHA5252 thermostatic switch (commonly called the 'otter switch'), fitted in the top of the inlet manifold and sensing coolant temperature directly. The switch closes (turning the fans on) at approximately 90°C and opens (turning them off) as the system cools. The switch is supplied complete with its 236022B sealing gasket. A failed otter switch is a common cause of overheating in stationary or slow-traffic conditions, the fans simply do not turn on when needed.
Renewing the switch is a routine job and should be the first item checked when investigating intermittent cooling problems.
Fan Relay and Wiring
Fan operation runs through the UKC5146 relay (now supplied as a black plastic relay), with circuit protection from the engine bay fuse box. Earth connections at the fan motors are particularly prone to corrosion and should be cleaned during any cooling-system service.
MGOC Spares
MGOC Spares supplies cooling fan motors, fan blades, the BHA5252 'otter' thermo-switch and gasket, the UKC5146 fan relay, fan-bracket fixings and all associated wiring components for the MGB GT V8.