@Ndungu,

 

the thermostat is much debated.... :-)

 

Am in a rush.....I'll give you my short opinion, why its needed and important :

 

1) Engine optimal temperature ensures less friction on moving parts

 

2) Engine Oil properties and correct viscosity are formulated for optimum temperature.

 

3) Fuel deposits. Cooler charge intake is better but achieved at optimum temperature.

 

4) On all Fuel injection engines, engine temperature sensor regulates excess fuel intake. Thus with no thermo, engine fuel intake will always be RICH until temp is reached, thus excess fuel burned and economy not much. More wear and tear at colder temps.

 

5) Your car front wind shield "defroster". You need the heater to remove moisture during rainy seasons.

 

I've listed things in a very basic way.... :-)