The Midget cooling system evolved significantly across production, with four distinct cooling layouts used during the car's life: the early vertical-flow system fitted to the 948cc and 1098cc engines, the early 1275cc vertical-flow system, the later 1275cc crossflow system, and the 1500 crossflow system carried over from the Triumph Spitfire. Identifying which layout is fitted to a particular car is essential when ordering radiators, hoses, water pumps, and thermostat housings, as components are not interchangeable between systems.
948cc and 1098cc Cooling
The earliest Midgets used a vertical-flow radiator with the top tank acting as both the coolant reservoir and the filler point. From 1965 an oil cooler became available as a factory option, mounted at the bottom of the air intake, with blanking grommets fitted to the bodywork where no cooler was specified. Oil was routed from the engine through the cooler and back into the filter. There was no thermostatic control of the oil cooler, although a blanking plate was offered to restrict cooler airflow during cold weather.
1275cc Vertical-Flow Cooling
Early 1275cc engines retained the vertical-flow radiator concept of the 1098cc, with a similar layout but matched to the higher cooling demands of the larger engine. The water pump, fan, and thermostat housing were specific to the vertical-flow arrangement, with the thermostat outlet pointing upward.
1275cc Crossflow Cooling
Later in 1275cc production, MG introduced a smaller crossflow radiator designed to operate at higher system pressure, allowing more efficient heat rejection from a more compact radiator core. The water pump was revised to suit the new layout, and the thermostat housing was redesigned with the outlet pointing to the left-hand side of the radiator. A six-blade plastic fan was adopted in place of the earlier metal item.
1500 Cooling
The 1500 cooling system was carried over from the Triumph Spitfire 1500 and is fundamentally different from any earlier Midget cooling arrangement. It uses a crossflow radiator contained within a black-painted steel cowling, an expansion tank mounted in the right-hand front corner of the engine bay, and a 15lb pressure cap. The cooling fan is a seven-blade plastic item specific to this engine. The home-market system capacity is 4.3 litres.
Radiators and Hoses
The radiator and coolant hose section covers all four cooling layouts. Radiators are available as direct replacements for each system, and uprated alloy radiators are stocked for owners requiring additional cooling capacity for fast road or competition use. Coolant hose kits are model-specific, comprising the top and bottom radiator hoses plus the bypass hose where applicable.
Water Pump, Fan and Thermostat
The water pump, cooling fan, thermostat, and fan belt section covers the engine-mounted cooling components, with separate sub-sections for the 1275cc and 1500cc. Water pumps differ between the vertical-flow and crossflow 1275cc layouts, and again for the 1500. Thermostat housings, gaskets, and the thermostats themselves are similarly model-specific.
Forlife Coolant
Forlife coolant is a long-life ethylene glycol-based coolant suitable for classic engines, providing both freeze protection and corrosion inhibition for the cast iron block, alloy components, and brass radiator core typical of the Midget cooling system. Unlike modern OAT coolants designed for contemporary aluminium engines, Forlife is formulated to be compatible with the mixed-metal cooling systems found in classic vehicles, where the wrong coolant chemistry can cause galvanic corrosion and rapid radiator failure.
Cooling System Upgrades
The upgrades and alternatives section covers electric cooling fan kits (which free up engine power and reduce noise), uprated alloy radiators, oil cooler kits in three sizes, oil thermostats, and silicone hose kits in a range of colours. These options suit owners using their cars for competition, sustained high-speed touring, or driving in hot climates where the standard cooling system may struggle.