Stewart,
I am using an OLD batch of castor Castrol. It was sealed in original tins for ten years and it appears more viscous in such a way to render unreliable a viscosity measurement. It does not presently mix with more than 15%kero, neatly separating in two phases , while the original oil was largely mixible when fresh, but I found that this old castor mixes easily when left sitting with kero for more than a month, shaking gently it time by time. Its runnig behaviour is regular, and it behaves well also with some modified olive.
I do not think a measurement of viscosity in its crude state being meaningful, sice it seems to show an excessive polymerization, that goes broken sitting with kero for making the mix.
Now I am going to test a new batch of modified sunflower, since it seems more viscous than unmodified one, reaching the viscosity of unmodified olive, but being appreciabily less tha modified olive.
I remain in doubt about what happens, someone seems to suggest that some free fatty acids are freed from the process of modifying. but I did not notice the residual glycerin increase that should result from it.
Ugo