That's funny, b/c my Volvo manual suggests using Castrol motor oil.
Hammond oil has to be of a certian wieght (it's a fairly light oil) and I'm sure that Hammond suggested using their oil so as not to create confusion about which oil to use. Although they obviously didn't manufacture the oil, they use a specific kind that works best with their machinery. (you wouldn't use car engine oil on a hammond).
Antifreeze has nothing to do with what kind of gas a car engine burns. You could just simply use water, except that it would freeze in the winter, and antifreeze has an anti-rust and lubricating agent that is better for long-term performance. It is contained in a system of pipes, radiator, and a pump (reffered to as a water pump, btw) that cools the engine and keeps it from overheating.