Why Use Cast Iron Making Engine Blocks?

Cast iron was usually used to make engine block because of its durability level, at one period of time Cast iron was the main basic building block of the automotive industry. Over the period of years cast iron was substituted for other material like aluminium with the basic idea of reducing the weight of a vehicle.

Cast iron generally means grey cast iron, but classify a big faction of ferrous alloys, which coagulate with a eutectic. Iron makes up nearly 95 per cent where as the key alloying agents are carbon and silicon.

The quantity of carbon in cast iron is anywhere between 2.1 per cent to 4 per cent cast irons also generally comprise of appreciable quantities of silicon, generally any where between 1-3 per cent. Due to its low melting point, good fluidity, castability, exceptional machinability and ware resistance, cast irons have gone on to become a vital engineering substance with a broad range of applications.

Cast iron is defined as an alloy of iron (Fe) and carbon (C) with the carbon content greater than 2 weight %. Other alloying elements may be added to enhance mechanical properties or ease processing.
Cast iron is used in engine blocks as it is much cheaper and easier to produce and manufacture than aluminium (Al). It also has superior wear resistance, vibration damping, higher yield point (stronger), greater toughness and a much higher melting point.
Most modern petrol engines (Otto cycle) now use aluminium engine blocks due to the significantly lower density of Al.
Diesel engine blocks, especially those used in the heavy trucking industry, are still made of cast iron. The diesel cycle runs higher pressures and temperatures than the Otto cycle. The types of cast iron used are mainly grey cast iron or compacted graphite iron (CGI).

Because it is stronger the aluminum thus the engine will last longer. Some cast iron machines are still running after 100 years after minimal servicing.

Cast iron does not bend, flex, distort, warp unlike other materials, however it is brittle and is thereofore more prone to cracking.

You have not answered the question!  Why cast iron ?  Why not mild steel?  Why not aluminum?