Why is a car engine made of iron?

Why is a car engine made of iron?
Car engines are mad from iron because it is material that is not only strong, but one the remains strong throughout heating and cooling. It has a constant rate of expansion and contraction at cold and hot temperatures, and can also be salvaged if exposed to overheating. However, some manufacturers increasingly, like Audi, BMW etc, are using aluminum blocks because of their superlative lightness. Aluminium does have disadvantages because unlike iron it cannot cope with extremes of temperature. This is clearly shown in Rover's K-series engines, which used an aluminum block, and often suffered from head gasket failure, and as a consequence, many engines were scrapped