•a new 3-D multi-physics coupling model is proposed for lubricated piston-liner systems.•The sub-models for mixed lubrication, spatial multibody dynamics, and heat transfer are fully coupled on a unified absolute coordinate frame.•The coupling model is discretized employing unified spatial and temporal discrete methods.•The occurrence of wear and failure on either side of the piston skirt is predicted by the model. In this paper, a new 3-D multi-physics coupling model is proposed for lubricated piston-liner systems. The sub-models for mixed lubrication, spatial multibody dynamics, and heat transfer are established and fully coupled on a unified absolute coordinate frame. The coupling model is discretized and solved using the unified spatial and temporal discrete methods. Then, an application example of a four-cylinder engine is employed to comprehensively investigate the coupling characteristics in the piston-liner system. The new coupling model reveals the presence of two distinct locations with the lowest local film thickness on either side of the piston's central axis, consequently yielding elevated local oil film pressures. This observation provides a reasonable explanation for the occurrence of wear and failure in the piston skirt on both sides. Display omitted