This article gives a option on the push towards lower viscosity engine oils.
http://www.machinerylubrication.com/Read/518/motor-oils#at_pco=smlre-1.0&at_tot=4&at_ab=per-1&at_pos=0
http://www.machinerylubrication.com/Read/518/motor-oils#at_pco=smlre-1.0&at_tot=4&at_ab=per-1&at_pos=0