Zinc dialkyldithiophosphate (ZDDP), the most widely used antiwear additive in engine oils, has been extensively studied over the last few decades. ZDDP forms surface-bound tribofilms at sliding contacts that prevent surface wear. Recent studies reveal that mechanochemical reactions drive tribofilm growth via stress and temperature. However, the individual effects of shear stress, compressive stress, and temperature on tribofilm growth is not yet fully understood. In this study, these driving factors were investigated separately by using different compositions of a high-viscosity, high-EHL-traction fluid mixed with a polyalphaolefin (PAO) basestock. This allows the compressive stress and shear stress to be independently controlled. Tribofilms were generated with a ball-on-disc tribometer in the elastohydrodynamic lubrication (EHL) regime for tungsten carbide (WC)/WC contacts with mixed sliding-rolling conditions. Shear stress and temperature were found to promote tribofilm growth exponentially. However, compressive stress had the opposite effect, slowing tribofilm growth. Mechanisms to explain these results will be discussed.