The MGA's cooling system circulates coolant through the engine block and cylinder head, through the radiator, and back to the water pump. All pushrod MGAs share the same fundamental layout, a front-mounted copper-and-brass radiator with an integral header tank, a mechanically driven four-blade fan bolted to the water pump pulley, a thermostat in the housing at the front of the cylinder head controlling coolant flow, and rubber hoses connecting the components. The system is pressurised by a cap on the radiator itself, raising the coolant's boiling point beyond the atmospheric boiling point of water. Cooling system capacity is approximately 10 Imperial pints (5.7 litres) with the heater circuit connected.
Electric fan conversion kits and aluminium radiator upgrades are available for owners wanting additional cooling capacity or modern reliability, and are covered under the Upgrades & Alternatives sub-category.
Radiator and System Pressure
The standard MGA radiator is a copper-and-brass unit with a top-fill header tank, produced to original specification for all pushrod variants. The radiator filler cap pressure was upgraded from 4 lb to 7 lb at chassis 71832 (July 1959) on the 1500, a change introduced specifically to address boiling under hard use. The 7 lb cap provides meaningfully more margin against boiling in hot weather or slow traffic. The 1600 was introduced in May 1959, so a small number of very early 1600 cars (chassis 68851 to 71831) also left the factory with the 4 lb cap; all cars from chassis 71832 onwards used the 7 lb cap.
Both caps are still available for owners restoring to a specific production period.
Twin Cam Cooling Differences
The Twin Cam cooling system differs significantly from the pushrod arrangement. The radiator sits further forward in the chassis to make room for the longer Twin Cam engine, and there was no space for an integral header tank, so a separate aluminium remote header tank is fitted on the left-hand side of the engine bay above the exhaust manifolds. The remote tank uses a non-pressurised cap, with a 7 lb relief valve fitted to the overflow pipe, added at chassis 652 in September 1958 and retrofitted to some earlier cars. The Twin Cam water pump is entirely different from the pushrod unit and is not interchangeable.
The Twin Cam thermostat opening temperature was lowered at engine 194 in June 1958; the location of the thermostat did not change. The different radiator position also affects the steering rack location, which sits further forward on the Twin Cam. None of the Twin Cam-specific cooling components interchange with the pushrod cars.
Cooling Hoses
The cooling hoses connect the radiator to the engine. The top hose carries hot coolant from the thermostat housing at the front of the cylinder head to the radiator, and the bottom hose returns cooled coolant from the radiator to the water pump inlet. Hose profiles differ between pushrod and Twin Cam installations owing to the different radiator and engine positions. Internal circulation when the thermostat is closed is provided by a bypass port within the thermostat housing itself, the MGA does not use a separate external bypass hose between the thermostat housing and the water pump.
All hoses should be inspected regularly for cracking, swelling, or softening, a burst hose at speed will empty the cooling system within minutes and can cause overheating and serious engine damage before the driver can stop.
Coolant
A long-life coolant formulated for mixed-metal systems, cast iron block and head, brass and copper radiator, steel hose fittings, is strongly preferred over standard modern antifreeze for the MGA. Modern low-silicate formulations developed for aluminium engines can attack the lead solder in the original radiator and heater matrix, accelerating corrosion and shortening service life. Forlife coolant and similar classic-car-specific formulations are stocked in the dedicated Forlife Coolant sub-category, providing freeze protection and long-term corrosion inhibition compatible with the period materials.
Ordering Considerations
When ordering cooling system components, the key identification points are pushrod versus Twin Cam (different radiator, hose profiles, thermostat and water pump), and for pushrod cars, the radiator cap pressure (4 lb on the very early 1500 before chassis 71832, 7 lb on all cars from chassis 71832 onwards). The water pump, thermostat, and fan belt are consistent across all pushrod variants. Twin Cam components are specific and not interchangeable with pushrod items. Electric fan conversion and aluminium radiator upgrades are available under the Upgrades & Alternatives sub-category for owners wanting additional cooling capacity for modern driving conditions. .