Hey people. Ok, I was at school today talking with one of the security guards who also happens to own a 1990 DeVille. So he goes on to tell me that his mechanic/friend used a mixture of castor oil and motor oil when it is time for an oil change. He then said that the guy told him that it is very helpful and it may as well change the time lengths at which you change your oil. Like instead of 3000 miles, the guy told him maybe 4000-5000 miles. He also told him that if everything goes well, you may not even have to. He wasn't so sure about not changing it, and neither was I. I've heard of people doing this before, but I just wanted to be sure about it before I tried it. I know castor oil provides an excellent lubricant. I decided to look to you guys first before I consulted someone else. SO, is castor oil and motor oil mixed a good thing? If so, then what kind?