More and more gasoline engines are using direction injection system to improve engine performance and to reduce fuel consumption.One of the potential negative effects of gasoline direct injection(GDI)is the increase of cylinder wall wetting,hence fuel dilution to the oil in the sump.Fuel diluted oil could cause lubrication failure and the common consequences include①low oil pressure due to low viscosity; ②oil film breakdown(in bearing or between piston/ring and liner due to low viscosity;③oil level increase with running time,hence higher churning loss; ④shorter oil life due to oil degradation and⑤loss of sealing effect(hence increase of blowby)etc.This paper will present investigation related to the oil dilution on oil pressure and bearing oil film thickness.