The water pump is bolted to the front of the cylinder block and driven by a V-belt from the crankshaft pulley, shared with the dynamo and the engine-mounted cooling fan, circulating coolant through the engine block and cylinder head, through the radiator, and back to the pump inlet. It is a centrifugal impeller type with a carbon-faced seal to prevent coolant leakage along the shaft. A failing pump typically announces itself through a weeping seal visible as coolant staining below the pump, a worn bearing producing a rumbling noise that increases with engine speed, or shaft play detectable by gripping the fan and checking for movement.
Pump Types & Fitment
Original MGA water pumps were of cast iron construction with a single bearing and a rear seal that sat against the pump body, and a rear seal is still available for owners rebuilding the original pump. The current replacement is a modern equivalent of the same mounting pattern and drive ratio but of updated internal construction, supplied ready to fit, and is common across all pushrod variants, the same item fitting the 1500, 1600, and 1600 Mk II engines. The Twin Cam water pump is of entirely different design owing to the Twin Cam's different block casting and coolant passage layout and is not interchangeable. The pump is secured to the block with short screws and longer bolts, spring washers, and a paper gasket between the pump body and the block face, and when fitting a new pump the gasket surface on the block must be clean and flat, as any residual gasket material will cause leakage.
Fan, Pulley & Fan Belt
The engine-mounted cooling fan is a six-blade metal unit bolted to the water pump pulley, which in turn bolts to the water pump shaft and takes the drive from the fan belt to rotate the pump and fan together. Fan, pulley, and mounting screws are available as individual replacement items.
For owners wishing to reduce engine load and improve warm-up time, an electric Kenlowe fan kit is available as an upgrade, with a separate thermo-switch kit to fit in the top hose. The fan belt drives the water pump and dynamo from the crankshaft pulley, tension adjusted by moving the dynamo on its mounting bracket, with correct tension allowing approximately half an inch of deflection at the midpoint of the longest run, as a loose belt slips and causes overheating and undercharging while an overtight belt accelerates bearing wear. The fan belt specification is common across all pushrod variants.
Thermostat & Housing
The thermostat controls coolant temperature by regulating the flow through the radiator, closed when the engine is cold so coolant circulates internally via a bypass port in the housing for rapid warm-up, then opening as the wax element expands to allow flow through the radiator. Three temperature ratings are available, 74°C for hot climates, 82°C as standard equipment, and 88°C for cold weather use, all three interchangeable in the same housing. The housing is bolted to the front of the cylinder head and carries the thermostat, the top hose connection, and the temperature sender for the dashboard gauge, the specification being consistent across all pushrod variants. On the MGA the bypass function is handled internally by a port within the housing, with no separate external bypass hose between the housing and the water pump, which is worth noting when sourcing parts, as a bypass hose listed for an MGB application is not required.
Ordering Notes
All pushrod variants take the same water pump, thermostat housing, fan belt, fan, and pulley, with the thermostat available in three temperature options to suit the operating environment. Gasket kits cover the pump-to-block gasket and other cooling system seals, and electric fan upgrades are available for owners seeking reduced engine load. Twin Cam cooling components are of different design and fall outside the standard pushrod range, so Twin Cam owners should contact the MGOC Spares team directly for specialist support.