The 1500 water pump is completely different from either 1275cc pump. It bolts to a separate water pump housing on the front of the engine block, with studs, nuts, and a gasket sealing the pump to the housing. The pump cannot be exchanged with any 1275cc unit, the mounting pattern, impeller, and housing are all unique to the Triumph engine.
1500 Cooling Fan
The 1500 cooling fan is a plastic item specific to this model. It mounts to the water pump pulley with bolts and spacers. The fan belt length (1088mm) is unique to the 1500 and is not shared with any 1275cc specification. As with the 1275cc, correct belt tension is critical, a slipping belt causes overheating, while an overtight belt damages the water pump seal and bearing.
1500 Thermostat Housing
The thermostat on the 1500 sits in a separate housing bolted to the water pump assembly, with a dedicated filler cap providing the coolant filling point for the system. This differs from the 1275cc arrangement where the thermostat sits in a housing on the cylinder head. Thermostats in the 82°C and 88°C ratings are available, with the 82°C unit being the standard UK specification. The thermostat housing gasket is specific to the 1500.