The K-series engine is an all-aluminium unit, and the cooling system includes an aluminium radiator, aluminium thermostat housing, and aluminium water pump housing. This extensive use of aluminium throughout the cooling circuit demands a coolant that provides effective corrosion inhibition for aluminium specifically, in addition to the usual anti-freeze and boiling point protection. The wrong coolant specification, or running the engine on plain water, can cause rapid internal corrosion of the aluminium components, producing a white oxide deposit that blocks narrow coolant passages in the radiator, heater matrix, and engine block, reducing cooling efficiency and accelerating the thermal conditions that contribute to head gasket failure.
Mixture Ratio and Capacity
The cooling system capacity on the MGF and TF is approximately 6.5 litres, though the exact capacity varies slightly between models and depends on whether the heater circuit is included. The recommended coolant mixture is typically a 50:50 ratio of antifreeze concentrate to clean water, which provides frost protection to approximately minus 36 degrees Celsius and raises the boiling point to approximately 108 degrees Celsius under atmospheric pressure. The system pressure cap further raises the effective boiling point. Over-concentrating the antifreeze beyond 60 per cent actually reduces the coolant's heat transfer efficiency, so more is not better, the 50:50 ratio represents the optimal balance between protection and cooling performance.
Coolant Change Interval
Standard antifreeze coolants should be changed every two years to maintain their corrosion inhibitor effectiveness. The extended coolant circuit of the MGF and TF, with its underfloor pipes and numerous connections, means that old or degraded coolant has more surface area to attack and more potential points of corrosion. When changing coolant, the system should be thoroughly flushed to remove any old coolant residue and any corrosion deposits. Draining the system requires attention to the underfloor pipes, which can retain old coolant if the car is not positioned to allow complete drainage.
Refilling requires careful bleeding to eliminate air locks, an air pocket in the extended circuit can prevent coolant flow to the engine and cause localised overheating with no indication on the temperature gauge until damage has occurred.
Bleeding the Cooling System
Air locks are the most common cause of overheating immediately after a coolant change or any work that involves draining the cooling system. The long underfloor pipe runs and the vertical height difference between the front radiator and the rear-mounted engine create natural air traps that are more difficult to purge than on a front-engined car. The bleed procedure typically involves filling the system slowly through the expansion tank with the heater set to maximum (to ensure coolant flows through the heater circuit), running the engine to thermostat opening temperature, and then topping up as air escapes.
Some owners and workshops use a vacuum fill system to pre-fill the circuit and eliminate air locks before starting the engine, this is a particularly effective approach for the MGF and TF layout.