The MGC's cooling system is fundamentally different from the MGB's conventional arrangement of the same era. Rather than a simple pressurised radiator with a combined filler and pressure cap, the MGC separates the filling and pressure functions across two components. The thermostat housing on the front of the cylinder head carries a plain non-pressure cap on a filler neck bolted to the housing by three screws with spring washers, sealed by its own gasket, this is used only for filling and topping up. A separate expansion tank, mounted on the front left-hand side of the engine bay below the radiator header tank, carries the pressure relief cap and is connected to the radiator by a hose, allowing coolant to expand into the tank as the engine warms and return as it cools.
This semi-sealed arrangement was introduced on the MGC three years before the MGB adopted a similar forward-mounted radiator and expansion tank system for the 1977 model year. The MGB GT V8, launched in 1973, also used a semi-sealed system inspired by the MGC's layout. No cooling system components, radiator, hoses, expansion tank, pressure caps, or filler neck, are interchangeable between the MGC and the contemporary MGB.
Expansion Tanks, Two Types by Market
Two different expansion tanks were used on the MGC, and they are not interchangeable. The standard tank for home market and most export cars takes a 10 lb pressure cap, while the tank fitted to USA and later Canadian cars (from 1968) takes a 14 lb cap, the higher pressure on North American cars reflecting the additional heat generated by emissions control equipment and the potentially more demanding driving conditions in warmer US climates. Each tank is retained by a clip and mounted on rubber pads with nuts and spring washers. The expansion tank hose is sold by the metre, with clips securing the connection at both the tank and the radiator ends.
An additional clip secures the hose to the fan cowl on its routing between the two components.
Radiator
The MGC radiator is mounted further forward than the MGB's, a change necessitated by the longer C-series engine occupying more of the engine bay. The radiator is available both new and as a reconditioned exchange unit on a one-for-one basis. It is secured to its mounting brackets by eight screws with spring and plain washers, with handed upper tie brackets (right-hand and left-hand) at the top and two lower tie brackets beneath. Each upper tie bracket uses a screw, spring washer, and nyloc nut; each lower tie bracket uses two nuts, spring washers, and plain washers.
A drain plug at the bottom of the radiator allows the cooling system to be drained. Fan cowl seatings are available for mounting the fan shroud, these require slight modification for use in the upper position.
Cooling Hoses and Bypass
The MGC uses specific top and bottom radiator hoses that are not shared with the MGB, the hose lengths and profiles differ owing to the MGC's forward-mounted radiator position and different thermostat housing orientation. Four hose clips are required for the radiator hoses, available as either original-style Supergrip wire clips for a period-correct appearance or modern worm-drive jubilee clips for ease of adjustment. A bypass hose with two clips connects the water pump bypass adaptor to the thermostat housing, maintaining coolant circulation through the engine block while the thermostat is closed during warm-up. Heater outlet hose is sold by the metre, with Supergrip or jubilee clips securing each connection.
Thermostat and Filler Neck
Three thermostat temperature ratings are available: 74°C for hot climates, 82°C as the standard UK factory fitment, and 88°C for cold climates, all fully interchangeable. The thermostat housing is C-series-specific, sealed by a gasket and secured to the cylinder head by two studs with nuts and spring washers. The filler neck is a separate component bolted to the housing by three screws with spring washers and fitted with a plain non-pressure cap. The split between filling point and pressure point is a key distinction from the MGB and worth familiarising with before routine topping up.
Kenlowe Hotstart and Water Wetter
A Kenlowe Hotstart unit pre-heats the engine to working temperature before starting using a 220 to 240 volt mains supply, eliminating the need for choke and providing instant cabin heat. Water Wetter is a heat transfer agent that can lower engine temperature by up to 15°C. One 335ml bottle treats 15 litres of coolant.