ORIGINAL: earlwb

A good grade of olive oil works as a substitute for castor oil. You want light or clear color extra virgin first press olive oil. The best is all pure and not a blend of various olive oils from around the world. Olive oil has similar traits to castor oil. It works in diesel and glow engines. Several people have run it in diesel engines, and a number of people have used it in model RC car glow engines.

The reason you don't see more people using olive oil in their engines is that we have way too many crooks who mislabel poor grades as being higher quality, lie about its origins, and doing other nefarious things with olive oil to boost their profits. Especially here in the USA, you just don't know what you get for olive oil. Too many companies are cheating with it.

Medicinal castor oil is the same as engine grade castor oil. But you have to be sure they didn't add sugar or flavoring to it first, you want the plain pure kind. Sometimes the cost at the pharmacy for castor oil is less than from the hobby shop, but sometimes it costs more though.