As the global energy transition moves to increased levels of electrification for passenger cars, then the number and role of hybrid electric vehicles (HEVs) increases rapidly. For these, the power reaches the road from an internal combustion engine (ICE) and/or an electric motor, with several switches between these three modes, over a typical drive-cycle. Consequently, this comes with a large increase in the number of significant engine stop and start events. Such events are potentially challenging for the HEV engine lubricant, as by comparison, for standard ICE cycles there is almost continuous relative movement of the two lubricated surfaces, for most areas of the engine. Based on both field and test cell observations, a challenging area for the lubricant within the gasoline direct injection (GDI) engine is the high pressure (HP) fuel pump, typically driven by a cam and follower, whilst lubricated by engine oil. From engine start, the speeds are low, also the fuel pump loads are high and transient. The loads continue to be variable and highly transient over a drive-cycle. A novel motoring friction test rig is described, which measures transient GDI HP fuel pump friction accurately. Using the same engine, further comparison data showing the contribution of this to engine friction is presented over the Worldwide Harmonized Light Duty Transient Cycle (WLTC), for both ICE and two types of HEV operating in charge sustaining mode (CS mode); lubricant friction differentiation in this area is shown. Based on measured data from vehicles tested on a chassis dynamometer, this friction rig runs from a controlled cold start, whilst also achieving the correct transient oil and coolant warm-up profiles. Further, it achieves the vehicle highly transient fuel flow, so the relevant transient GDI pump cam loading, over the WLTC. The frictional energy required is used to compare engine lubricants.