There is a myth that is quite popular in some countries with hot climate, even among mechanics; "cooling system's thermostat is not needed in the car".
This believe is not necessarily true even though the importance of the thermostat is not as much as it is in a car in a cold climate.
SOME OF THE EFFECTS OF THERMOSTAT DELETE
The engine does not warm up on time. One function of the thermostat is preventing the coolant from circulation until the engine has attained a particular temperature. When the thermostat is not in place, the coolant begins to circulate right from the moment the engine is started. This extends the time the engine takes to attain operating temperature. The cooler the ambient temperature, the more time it will take to attain operating temperature.
The friction between the piston rings and the cylinder walls is increased hence the engine wears faster. This effect is more pronounced in colder climates.
The car stays in open loop for a longer period. In open loop, there is no feedback control by the air to fuel ratio sensors (oxygen sensors). It is a fuel enrichment phase. The more time the car uses in open loop phase, the more the fuel consumption.
Similarly, the cooling system will not be able to also transfer heat to the transmission during warm up to bring up the automatic transmission to operating temperature fast. If the thermostat is not there, transmission cooling starts immediately the engine is started. This increases wear in the transmission and hence transmission lifespan reduction.
In cold mornings or during the rainy season of harmattan when the weather can be cold even in the afternoon, the engine can be overcooled even though the cooling fan system is working well. In this situation, the cooling fan is turned off by the controller and just the outside cold air is enough to cool and over cool the engine. Indepth article on this can be read in causes of car engine overcooling.