The 1275cc water pump, fan, and thermostat configuration varies within the 1275cc range depending on the engine prefix and the cooling system layout (vertical-flow or crossflow). The vertical-flow water pump (GWP132) was fitted to all 12CC and 12CE engines (1967 through August 1971), while the crossflow water pump (GWP134) was introduced with the 12V-prefix engines in August 1971 and continued to the end of 1275cc production. The two pumps differ in their impeller design and housing geometry to suit the corresponding radiator layout, fitting the wrong pump for the cooling system in use will compromise circulation. The crossflow radiator itself was introduced earlier, in December 1968 at GAN4-66226, but cars built between December 1968 and August 1971 retained the vertical-flow water pump despite running a crossflow radiator.
Cooling Fan
The 1275cc cooling fan is a six-blade item throughout production, with early cars using a metal fan and later models a plastic fan. The plastic fan is widely regarded as a superior upgrade where the metal item is still fitted, offering improved durability and reduced risk of radiator damage. Both bolt to the water pump pulley, which also drives the fan belt. Three fan belt lengths were used across 1275cc production, 863mm, 838mm, and 813mm, with the correct length determined by whether the car has a dynamo or alternator and the pulley diameter fitted.
A loose fan belt will slip, causing overheating and undercharging; an overtight belt will overload the water pump bearing and dynamo/alternator front bearing.
Thermostat
Thermostats are available in 74°C, 82°C, and 88°C ratings. The thermostat gasket and housing cover differ between the vertical-flow and crossflow systems, the vertical-flow type has the outlet pointing upward, while the crossflow type directs the outlet to the left-hand side of the radiator. A bypass hose between the water pump housing and the thermostat area maintains coolant circulation through the engine when the thermostat is closed during warm-up.