Aluminum expands @ 229 C to remove engine bearings easy But a engine will never get that hot under normal operating temperature. Not even close. Fuel without castor oil will discolor after burning. So it isn't castor oil that burns. It's the ingredients that the manufacture puts in the oil lube blend that is causing the burn. I have used may brands of fuel with and without castor oil . Sig, Redmax, Omega, Byron(crap) Wildcat and S$W. Non of these I nave never seen burning.. So it comes down to the brand and blend! So you can keep on blaming castor oil for the burning but it doesn't BURN under operating temperatures! I have even started making my own blend of fuel. Only 3-4 ingredients. No burning yet.