The MGB cooling system evolved throughout production, with changes to the radiator, system pressure, fan configuration, cooling hoses, and water pump. Understanding these differences is important when selecting replacement parts to ensure compatibility with your specific engine and cooling system layout.
Radiators & System Configuration
Early MGB models from 1962 to 1967 used a rear-fill radiator, where the filler cap was located at the back of the header tank on the engine side of the diaphragm panel, a design that made it difficult to visually confirm coolant levels when topping up. In 1967, with the introduction of the MkII, MG adopted a centre-fill radiator, allowing owners to see the coolant level more easily while also introducing a revised thermostat housing outlet pointing to the left-hand side of the radiator. MGBs up to September 1976 used mechanical engine-driven cooling fans of varying types along with radiators that had limited expansion space.
From September 1976 onwards the system was redesigned with a separate expansion tank and a higher-pressure 15lb cap, creating a sealed no-loss cooling system. At the same time, the traditional mechanical fan was replaced by a thermostatically controlled electric fan, improving airflow while reducing engine drag.
Cooling Hoses
Across production there are three main cooling hose configurations, which correspond with the rear-fill, centre-fill, and later electric fan radiator assemblies. The hoses are not interchangeable between these configurations, and complete hose kits, including Kevlar-reinforced and silicone options, are available for each.
Cooling Fans
The mechanical cooling fan changed several times during production. The earliest cars used a three-blade metal fan, painted yellow. A six-blade metal fan was fitted to North American specification and automatic gearbox cars from 1967.
In December 1972, North American cars adopted a seven-blade plastic fan, and from March 1974 the fan type was finally commonised across the range with a seven-blade plastic fan with metal inserts. The original three-blade fan was briefly reinstated on Swiss-market cars from October 1974 to meet local noise regulations.
Water Pumps
During production the MGB was fitted with four different water pump types. Three main bearing engines (18G, GA) from 1962 to 1964 used a unique pump. Five main bearing engines (18GB, GG) produced from 1964 to 1971 used a different type, with all 18V engines from 1971 to end of production using a third. It is not uncommon for owners to order the incorrect water pump, owing to components having been altered from standard during a previous rebuild.
Where this arises, it may be necessary to measure the depth of the water pump from the engine block face to the rear of the pulley to confirm compatibility. The later 18V pump supersedes the original 18V chrome bumper type, but requires different mounting screws when fitted in its place.
Thermostats & Housings
The thermostat housing cover also changed across the three cooling system configurations, rear-fill radiator cars, centre-fill radiator cars, and post-September 1976 electric fan cars each use a different cover. Three thermostat temperature ratings were available throughout production, 74°C for hot climates, 82°C as standard, and 88°C for cold climates, all fully interchangeable. The MGOC Spares range encompasses cooling system components including radiators, aluminium radiators, coolant hoses, hose kits, pulleys, mechanical fans, thermostats, thermostat housings, water pumps, and expansion tanks. Plus a proven range of performance upgrades such as Revotec electric fan kits, silicone cooling hoses, Forlife coolant, and aluminium radiators designed to improve cooling efficiency and reliability.
A full engine prefix reference table is available to help identify which cooling system configuration applies to your car.