lower viscosity oil

[aerohead]

If you run a viscosity lower than what is specified for your particular engine you can destroy it in the quest for higher mpg.
Under strong loading,the hydrodynamic film which separates moving parts from one another can be literally squeezed out allowing the condition known as asperity,where dry contact is achieved.
Without the metal surfing on the film of oil,the tops of the micro structures of journals and babbit will 'high-point',momentarily spin-weld together,break apart,then repeating,in a cascading rapid death spiral ending in a ruined engine.
Don't lose a $3,000 long block in your quest for mpg,and find yourself with your thumb out trying to hitch a ride home.