ranchpig...synthetics start to burn at about 450F but castor is about 550F so it'll stay a liquid longer. When synthetics get hot they break down immediately into the various chemicals that were used to make them. When castor gets hot enough to break down it turns into yet another lubricant. It keeps doing this until you get to the dreaded varnish which just happens to be a lubricant as well

But medicinal castor is no good because it's had an extra refining process that takes most of the good lubricating qualities out of it.