From September 1976, the MGB cooling system was redesigned and the traditional mechanical engine-driven fan was replaced by a thermostatically controlled electric fan mounted on brackets in front of the radiator. This change was part of a broader revision that also saw the radiator moved forward, a separate expansion tank introduced, and the system pressurised to 15lb with a sealed no-loss arrangement. The electric fan operates independently of engine speed, cutting in only when the coolant temperature reaches a set threshold and switching off once the temperature falls. This offers several advantages over the mechanical fan, it reduces parasitic drag on the engine when cooling is not required, allows the engine to warm up more quickly, and provides cooling even when the car is stationary in traffic, where a mechanical fan spinning at idle speed delivers minimal airflow.
The fan blows cold air onto the radiator from the front, rather than drawing it through from behind as a mechanical fan does. The thermostatic switch is fitted to the radiator header tank and controls when the fan engages. Two types were used across later production, an earlier type with pin terminals and a later type with spade terminals, introduced from around 1980. The correct seal and, on later switches, a retaining clip are required to ensure a watertight fit in the header tank.
A terminal kit is also available for wiring connections. The switch should be tested periodically, as a failed switch will prevent the fan from operating and can lead to rapid overheating, particularly in slow-moving traffic where there is no natural airflow through the radiator. The fan motor, fan blade, and guard are all available individually. A mesh-type fan guard is fitted between the radiator and the bonnet locking platform as a safety measure, preventing fingers or tools from coming into contact with the fan blade, which can operate at any time when the ignition is on and the engine is at temperature, regardless of whether the engine is running at the time.
The motor bracket and lower clamp secure the fan assembly to the radiator and are also available separately.
Aftermarket Electric Fan Kits
For owners of pre-September 1976 cars who wish to convert from the mechanical fan to an electric setup, aftermarket electric fan kits are available. These kits operate thermostatically, cutting in only when required, and offer the same benefits as the factory electric fan system: improved engine warm-up, reduced fan noise, and the elimination of the engine power absorbed by a belt-driven fan. A separate thermostatic switch kit is available for fitting into the top radiator hose, providing the temperature-sensing trigger for the aftermarket fan independently of the radiator. The MGOC Spares range covers all the components needed for both the factory electric fan system on post-1976 cars and aftermarket electric fan conversions for earlier models.