From September 1976, the MGB cooling system was significantly redesigned. The radiator was moved forward and a thermostatically controlled electric fan replaced the mechanical engine-driven fan. A separate expansion tank was introduced, pressurised with a higher-rated 15lb cap, creating a sealed system.
These changes altered the cooling hose layout, and the hoses used on post-September 1976 cars are not interchangeable with the earlier mechanical fan configurations. The top and bottom radiator hoses on electric fan cars are both different from the earlier types, reflecting the revised radiator position and connection points. The expansion tank is connected to the radiator by a small-bore hose, and an overflow hose runs from the expansion tank to allow coolant to vent safely if the system overpressures. These additional hoses are specific to the post-1976 system and should be inspected alongside the main radiator hoses during any cooling system maintenance.
The expansion tank itself is available in both the original metal type and a plastic alternative. The radiator cap on these cars is a 15lb rated item fitted to the expansion tank rather than to the radiator itself, a distinction from the earlier 10lb cap fitted directly to the radiator on pre-1976 cars. Using the incorrect cap pressure will affect the system’s ability to maintain the correct operating temperature and can cause premature coolant loss or overheating.
Electric Fan & Thermostatic Switch
The electric fan is controlled by a thermostatic switch fitted to the radiator. Two switch types were used across later production, an earlier type with pin terminals and a later type with spade terminals, and the correct seal and clip should be matched to the switch fitted. The fan motor, fan blade, guard, and mounting brackets are all available individually. A complete Kevlar-reinforced cooling hose kit is available for the post-September 1976 configuration, providing all the hoses and clips needed for a full system renewal in one package.
As with the earlier configurations, Kevlar reinforcement offers improved resistance to collapse and deterioration compared to standard rubber. Hose clips are available in both worm-drive and original-style wire types, in the sizes used on this cooling system. When renewing hoses, it is advisable to flush the cooling system thoroughly, inspect the radiator and expansion tank for corrosion, check the thermostat and water pump condition, and verify that the electric fan and its thermostatic switch are operating correctly. A cooling system that has been neglected internally, with scale, corrosion, or degraded coolant, will shorten the life of new hoses and compromise the system’s ability to regulate engine temperature.