The MGC water pump is an entirely different component from the MGB unit, designed specifically for the C-series engine's cooling system layout. The pump is mounted on the front of the engine block and driven by a V-belt from the crankshaft pulley, also driving the cooling fan from the water pump pulley. The C-series pump circulates coolant through a longer and more complex path than the MGB's system, from the pump through the engine block water jacket, up through the cylinder head, out through the thermostat housing to the radiator, and back to the pump via the bottom hose, with additional circuits serving the heater and the bypass loop. The pump's impeller diameter and flow rate are specified for the six-cylinder engine's greater coolant volume requirements, and the bearing and seal assembly is designed for the higher operating loads of driving a larger fan on a heavier engine.
Pump Replacement & Adaptors
The water pump is available as a new assembly, supplied without the two adaptors that must be transferred from the old pump or ordered separately. A heater system adaptor with a sealing washer provides the connection for the heater hose circuit, screwing into the pump body and accepting the hose that feeds hot coolant to the heater matrix. A bypass adaptor with sealing washers maintains the coolant circulation path between the pump and the thermostat housing when the thermostat is closed during warm-up, without which the engine would overheat locally at the cylinder head.
When fitting a new pump, the sealing washers on all adaptors should be renewed, as reusing old copper or fibre washers that have been compressed and work-hardened risks a slow coolant weep that can be very difficult to trace once the engine bay is fully assembled. The water pump gasket seals the pump to the engine block face, and five bolts with spring washers secure the pump to the block.
Pulley & Fan Belt
The water pump pulley drives both the pump and the cooling fan from the crankshaft via a single fan belt, the fan mounting to the front face of the pulley via a spacer and screws. Correct belt tension is critical, as a slack belt slips under load, reducing both pump flow and fan speed when maximum cooling is needed, while an over-tightened belt overloads the water pump and alternator bearings. The belt should deflect approximately half an inch under firm thumb pressure at the midpoint between the two pulleys, and should be checked regularly for cracking, glazing, or fraying.
Thermostat
Three thermostat temperature ratings are available, 74°C for hot climates, 82°C as standard, and 88°C for cold climates. The standard 82°C thermostat was the factory fitment for UK market cars and is the correct choice for most British driving conditions. The 74°C allows the engine to run cooler and suits consistently warm climates or performance-modified engines, while the 88°C brings the engine to a higher operating temperature more quickly, beneficial in cold climates where the engine struggles to reach its optimum temperature. All three ratings are fully interchangeable.
The thermostat is housed in a casting on the front of the cylinder head, sealed by a gasket and held by two studs with nuts and spring washers.
Filling Point & Dual-Cap System
The thermostat housing also serves as the cooling system filling point, with a filler neck bolted to the housing by three screws with spring washers and sealed by its own gasket. A plain non-pressure cap is fitted to the filler neck for topping up only, while the pressure-rated cap is located on the separate expansion tank mounted on the front left-hand side of the engine bay. This dual-cap arrangement is a key difference from the MGB, as filling and checking the coolant level is done at the thermostat housing filler neck, not at the expansion tank, and the expansion tank cap should not be removed when the system is hot, as it is under pressure.