About this sentence:
Der Motor des Autos hat viel zu wenig Öl. Infolgedessen ist er kaputt gegangen.
Why it is er not es?
As I know er means he in English. So, es should be used as it in English.
Whilst German and English grammars share many features, you face now something which is radically different: gender. Motor, in your example, is masculine. Therefore the pronoun should be also masculine, er (alternatively der). German does not quite obey English-pronoun rules regarding whether you treat an object or a person.