•Fuel-saving effect of ORC-WHR facilities on trucks are comprehensively evaluated.•Fuel-saving effect degradation due to existing components’ limitations is examined.•Fuel-saving effect degradation due to interactions in system integration is studied.•Effects of system dynamics and control strategies are explored.•It is suggested the system power density should be greater than 70 W/kg. Recovering and converting the waste heat within the exhaust gas of high-density diesel engines to mechanical or electrical energy using an organic Rankine cycle is a hotspot in recent years, and many optimistic views towards the fuel-saving capacity of this technology have been reported. But considering the off-the-shelf components’ limitations, system integration, dynamics, and other attached penalties, there lacks a comprehensive evaluation yet, especially in driving cycle scenarios. For this, a heavy truck co-simulation platform is built, embedded with organic-Rankine-cycle-based exhaust heat recovery models. Based on that the fuel-saving performance of organic Rankine cycle facilities are evaluated and main losses due to limiting factors are also discussed. It is found that an ideal subcritical organic Rankine cycle system improves the truck’s fuel economy by 4.48–7.52% when it is fully loaded. But due to the performance limitations of existing components and system interactions, the fuel-saving effect is reduced from 7.52% to 3.5%. Further considering organic Rankine cycle system dynamics and control operations, this value degrades to 2.07–2.24%, and it continues to decline with the attached weight. It is suggested that the system power density should be greater than 70 W/kg at least. At this point, its fuel-saving effect is just 1.75%.