Reg,
From my readings, mosy if not all vegitable oils will form varnish as the temps go up , but the amount and at what temp varies. Vegi oils like canola, peanut and other cheap oils commonly used in comercial cooking tend to be on the low end of the list. Olive oil (maybe others) tends more to castor but with a lower viscosity, modding the olive oil increases its viscosity some( which from my tests seems to be enough) as well as its ability to form larger chain molecules( ie form varnish)
Now apparently modding olive oil is not a new idear, it was used dureing WW1 as an alternative to castor oil in times of shortage.
There are other vegitable oils with similar viscosity to castor due to similar saturated fat levels, but these oils tend to "Dry"/ form varnish at too gigh a rate to be of use to us- they are used in paints as driers!
Castor is the only highly/fully saturated fat vegi oil that doent dry, and the funny thing is that olive oil even though being one of the least saturated vegi oils , modds to be similar to castor.
You noted previously that with the cheap(cooking) oils mechanical noise was higher - i found this also, but with modded olive oil the motor ran as if on castor, I also found this, but also found the olive oil still had the clean running properties of the cheaper oils as well as the easier starting qualities but not so much as the cheap oils- viscosity related I think.
Anyway I dont think that we need be too concerned with lean runs so much as whether the viscosity is sufficient for the job, and as I said previously the viscosity required is dependent on materials and fits and construction/design of the motor in use- motors with large brg surfaces will get away with lower viscosity oils as the loads are distributed over larger areas.
Motors with small dia wristpins should probably stick with useing castor , wereas motors with substantial brg surfaces will do ok on allternative oils.
Stewart