The Midget radiator and coolant hose arrangement varies according to which of four cooling layouts is fitted to the car. Identifying the correct layout before ordering is essential, a vertical-flow radiator cannot be substituted for a crossflow item, and the corresponding hoses, pressure cap, and mounting brackets are different in each case. Cars are usually identifiable by year, but engine swaps and previous repairs can mean the cooling system fitted is not always the original specification.
948cc and 1098cc Radiators
The earliest Midgets fitted with the 948cc and 1098cc A-Series engines used a vertical-flow brass and copper radiator with the top tank acting as the coolant reservoir and filler point. The radiator is mounted on a cradle bolted to the front of the inner wing structure, with a top hose to the thermostat housing and a bottom hose to the water pump inlet. A bypass hose between the water pump and cylinder head maintains coolant flow when the thermostat is closed.
1275cc Vertical-Flow (1967 to 1968)
Early 1275cc cars retained a vertical-flow radiator broadly similar in layout to the 1098cc but with cooling capacity matched to the larger engine's higher heat output. The thermostat housing outlet points upward, and the top hose connects directly to it. The radiator filler is on the top tank with a 7lb pressure cap originally specified, although uprated 13lb caps are commonly fitted as a service item.
1275cc Crossflow (1968 to 1974)
From 1968 onward, the 1275cc adopted a more compact crossflow radiator with the top and bottom tanks at left and right, allowing a lower bonnet line and improved cooling efficiency at higher system pressure. The thermostat housing was redesigned with the outlet pointing horizontally to the left, feeding into the radiator's left-hand tank. The crossflow radiator runs at a higher pressure (13lb cap) and uses a different hose set from the vertical-flow system. The two radiator types are not interchangeable.
1500 Cooling Layout
The 1500 Midget uses the Triumph Spitfire 1500 cooling system: a crossflow radiator mounted within a black-painted steel cowling, with a separate plastic expansion tank in the right-hand front corner of the engine bay. The expansion tank carries a 15lb pressure cap, and coolant top-up is via the expansion tank rather than the radiator filler. The 1500 hose set is unique to this engine and shares no parts with any 1275cc layout.
Pressure Caps
Pressure caps are critical to the cooling system's operation, they raise the coolant boiling point under load by maintaining system pressure, and they release excess pressure to the overflow if the system overheats. The original cap rating must be matched to the radiator: a higher-pressure cap fitted to an older or weakened radiator core may rupture the tank or split a seam. A new cap should be fitted whenever the radiator is renewed or recored, and at any sign of coolant loss with no visible leak.
Coolant Hoses
Hose kits are model and layout-specific, comprising the top radiator hose, bottom radiator hose, bypass hose, and heater hoses. Original-pattern moulded rubber hoses in correct profiles are stocked for each cooling layout. Silicone hose kits are available as an upgrade in a range of colours, offering longer service life, better resistance to oil and ozone, and a tidier engine bay appearance, particularly suited to restored or show cars. Hose clips of various types are stocked separately, with original-pattern wire-form clips available for concours restoration where the modern worm-drive clip would be incorrect.
Radiator Recoring and Replacement
The original brass and copper radiator cores can be recored by a specialist if the existing tanks are sound but the core itself is blocked or leaking, typically more economical than full replacement and preserving the period-correct appearance. Where the tanks have corroded or split, a complete new radiator is the better option. Aluminium replacement radiators are available for owners seeking maximum cooling capacity, particularly suited to fast-road or competition use, although they alter the engine bay appearance from original.