<p>Climate change owing to global warming caused by human activities has raised concerns worldwide. The primary cause of global warming is increased emissions of carbon dioxide (CO₂) into the atmosphere. There is growing emphasis on strengthening emission regulations, particularly in the transportation sector, to reduce CO₂ emissions and their environmental impact. Several studies are currently underway to address escalating CO₂ emission regulations while also improving engine thermal management and fuel efficiency. In this study, the characteristics of coolant flow rate, heat rejection and fuel consumption based on coolant temperature were experimentally analyzed using engine tests in a different test-cell environment. In addition, a preliminary experiment was conducted to compare the differences in cooling performance and fuel consumption using two types of systems: the cooling system of a real vehicle and a coolant external control system in an experimental test cell environment. After confirming that there was no significant difference in the average cooling performance and fuel consumption between the two cooling systems, the results were compared and analyzed based on the engine speed and coolant temperature using only the external control system.</p>