As far as I know about lubrication the ideal oil should have stable viscosity at all conditions e.g. temperature, pressure and etc. To be more precise it should have the viscosity of hot oil at cold start let say 15cSt. For our beta engines it should be even slightly "thicker" to maintain proper oil pressure. Unfortunatelly that products so far does not exist and still remains the "holy graal" for all petrolheads... The best available approximation would be 0W60 for good quality synthetic esters. Regular oils, especially mineral ones have, unfortunatelly, strong temperature related viscosity. This means they are almost not flowing at extreme cold temperatures and on the other hand at running temperatures they become too thin, not maintaning the proper protection against wear.