Answer
Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, many thanks for your question that shows your keenness to follow the teachings of Islam.
According to some scholars, it is permissible to benefit from pork fat in producing some products that are not eaten, such as car oil.
In his response to your question, Sheikh `Abdul-Majeed Subh, a prominent Azharite scholar, states:
Some scholars are of the opinion that ingesting the flesh of swine is the only prohibited thing that is meant in the Qur’anic verse, which reads, “Say: I do not find in that which has been revealed to me anything forbidden for an eater to eat of except that it be what has died of itself, or blood poured forth, or flesh of swine– for that surely is unclean– or that which is a transgression, other than (the name of) Allah having been invoked on it; but whoever is driven to necessity, not desiring nor exceeding the limit, then surely your Lord is Forgiving, Merciful.” (Al-An`am 6:145)
Moreover, the Prophet (peace and blessings be upon him) allowed people to make use of the skin of a dead animal after it had been tanned. It was narrated that Ibn Al-`Abbas said: A sheep was given in charity to the freed slave woman of Maymunah, and it died. The Messenger of Allah (peace and blessings be upon him) passed by it, and said: “Why do you not take its skin, tan it and make use of it?” They said, “It is dead meat.” He said, “It is only haram (unlawful) to eat it.” (Muslim)
Therefore, depending on this hadith, benefiting from pork fat in manufacturing car oil is permissible.
Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, added:
It is only prohibited to eat pork, but burning its fat in cars and other machines is permissible. Manufacturing it for this purpose is also permissible.
Almighty Allah knows best.