3 port thermostat with 79°C opening temperature. This is a recommended lower temperature version of the type originally fitted to Scorpion and early Montecarlo S1 cars.
On later Montecarlo cars, a 3 port thermostat can be used to replace the factory 4 port version with a modification to the heater return hose connection - the hose needs to be routed to the water pump by
either replacing the pump 2 port flange with a 3 port flange from early cars
or by joining into the lower expansion tank hose via a Tee piece hose adapter such as
CO311.