A thermostat responds to changes in temperature by allowing, restricting or totally blocking coolant circulation from the engine to the radiator.
Climate is a long term weather or atmospheric condition of an area. Some parts of the globe are known to be hot, some are very cold while others have average temperature.
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.
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.
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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.
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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.
The transmission won't warm up on time. The engine and transmission shares same cooling system in many cars. The transmission is cooled by the engine's radiator through the heat exchanger by transferring heat from the automatic transmission fluid to the coolant when the transmission needs cooling.
It causes quicker degradation of the engine oil. When the engine cannot attain the optimum temperature where moisture in the engine oil cannot be burnt off, the engine oil degrades faster which can cause engine wear as the car owner is still likely to stick to the recommended oil change interval (OCI) which is the time the oil is suppose to be in service usually in miles or kilometers. For instance, change of engine oil after 3,000 miles or after 6 months, whichever comes first.
There will be increased emissions which is detrimental to human health and the environment.
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The engine might start oil consumption and smoke quicker as the rings wears faster.
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There is increased cost of ownership as owners or users will spend more money on fuel and parts replacement (for example rings).
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Engine's lifespan reduces. A gradual cummulation of these factors over time causes reduction in the lifespan of the engine.
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Keeping the thermostat in place is one good way of making the engine to last long and that reduces running expenses.