Andy, Stewart and Sloper, thanks for your replies.
I am not sure of the possibility of using olive oil alone, because the resulting viscosity should be rather low, but what appears the interesting is that ,by mixing with appropriate proportions of castor ,one can vary the working viscosity matching better his engine/flying needs. This seems really an appealing way to better mixes.
As for adding mineral or synthetic oil, the matter can be really different since these oils differ widely also between them.
A stone in a pond: DID ANYONE USE FOR MIXES BIO CHAINSAW LUBES? Some of them have very interesting properties at high temperatures and are listed at prices cheaper than olive oil. I am searching for them, but BIO (vegetable) and not mineral biodegradable ones.