High-blend biodiesel and renewable diesel are increasingly recognized as viable drop-in fuels for heavy-duty diesel engines to meet stringent emission reduction targets. This study experimentally investigates the effects of conventional diesel (B0), diesel–FAME blends (B40F–B70F), and diesel–HVO blends (B40H–B70H) on engine performance, exhaust emissions, and short-term wear characteristics. Tests were conducted on a production heavy-duty Komatsu SAA12V140E-3 engine under controlled operating conditions over a wide range of engine speeds. Engine performance was evaluated in terms of brake torque, brake power, brake thermal efficiency, and brake-specific fuel consumption, while emissions of CO, NOx, O₂, and CO₂ were measured. The results show that increasing the FAME blending ratio leads to noticeable performance deterioration. At higher blend levels (B60F–B70F), brake power and thermal efficiency decrease by approximately 5–10%, whereas fuel consumption increases by 12–25% relative to B0, primarily due to the lower heating value and higher viscosity of FAME. In contrast, diesel–HVO blends exhibit performance comparable to conventional diesel, with reductions in power and efficiency generally below 5%. All biofuel blends reduce CO emissions by approximately 8–20%; however, FAME blends show a more pronounced increase in NOx emissions at higher blending ratios, whereas HVO blends provide a more balanced emission profile. Wear metal concentrations in used lubricating oil remain below critical limits for all tested fuels. Overall, the results indicate that HVO offers superior compatibility as a high-blend renewable fuel for heavy-duty diesel engines, achieving favorable performance–emission trade-offs without requiring engine hardware modifications.