Graham,
I did many hrs seaching for info on vegi oils(wished ied saved more of the info and links)
The only reason I can see to use soybean oil for makeing automotive lubricants is price, olive oil is wayyyyyyy more expensive. initial commercial tests with vegi oils used mineral oil additives with limited results. More recent tests/products are useing additives that have been specifically developed to get the best out of the base oil.
Now my reasons for modding the olive oil , I chat online to a bio chemist , I had told her of the priocess we had found to mod the cheap vegi oils , she confirmed this was the correct thing to do . Later I asked what vegi oil other than castor would make the best lubricant, without hesitation she said olive oil as thick as i can find, and also to increase the glycerine used in the modding process as olive oil is very low in saturated fats (the glycerine increases saturation level of the fats in the oil). Im no bio chemist but she is (she runs a gov lab with 15 other chemists/technitions) so i figured she was right. My test runs with the modded olive oil indicated the viscosity was suffient in the test motor (based on mechanical noise with both castor and olive oil lube)
But as I have said previously the required viscosity required for reliable opperation is engine dependent. I'm a motor mechanic and diesel fitter and am pretty good at identifying sources of mechanical noise and weather its normal or too harsh.
I can only say in the motor tested the olive oil was ok to use, the fuel blend was 20% oil 20% ether , 60% kero., the motor was hand started- started easily useing a normal prime technique, needle needed to be screwed in about 1/3 turn and compression down about 1/4turn from running regular old english mix.
Stewart