The Triumph Stag is a 2+2 sports tourer which was sold between 1970 and 1978 by the British Triumph Motor Company, styled by Italian designer Giovanni Michelotti. The car was launched one year late in 1970, to a warm welcome at the various international auto shows. The Stag rapidly acquired a reputation for mechanical unreliability, usually in the form of overheating. These problems arose from a variety of causes. First, the late changes to the engine gave rise to design features that were questionable from an engineering perspective. For example, the water pump was set higher on the engine than is usual. If the engine became hot in traffic, and coolant escaped from the cooling system via the expansion bottle, the reduced volume of fluid left when the engine cooled down again fell below the level of the pump, which would eventually fail as a result. Water pump failures sometimes occurred due to poorly-hardened drive gears, which wore out prematurely and stopped the water pump. A second cause of engine trouble was the lack of attention to corrosion inhibitor in the coolant. The block was made from iron and the heads from aluminium, a combination that required the use of corrosion-inhibiting antifreeze all year round. This point was not widely appreciated by owners or by the dealer network supporting them. Consequently, engines were affected by electrolytic corrosion and white alloy oxide sludge collected in radiator cores, reducing radiator efficiency and causing overheating. The result was head gasket failure due to cylinder head heat distortion, a very expensive repair. Owners would usually get their repaired cars back with the radiator still clogged, leading to repeat failures. A third cause of trouble was the engine's use of long, simplex roller link chains, which would first stretch and then often fail inside fewer than 25, 000 miles (40, 200 km), resulting in expensive damage.
