This study investigates the effect of engine warm-up time on the emissions of hydrocarbons, carbon monoxide, and nitrogen oxides. Data were analyzed under eight different engine speeds and two load conditions (15% and 30%) over a 15-minute period, in both thermostat and non-thermostat configurations. The results indicated that at 1,500 rpm and 15% load, installing a thermostat reduced the warm-up time by up to 29%. On average, increasing engine speed by 500 rpm shortened this time by 27% at 15% load and by 32% at 30% load. Furthermore, hydrocarbon emissions were substantially elevated during the first three minutes after start-up but stabilized within the range of 150–250 ppm once warm-up was complete. Nitrogen oxides exhibited the most significant variation: doubling the engine speed from 1,500 to 3,000 rpm tripled their concentration, and doubling the load increased it by approximately a factor of 1.6. Moreover, under low-speed and low-load conditions, installing a thermostat reduced carbon dioxide emissions both during and after the warm-up period. Ultimately, it can be concluded that shorter warm-up times, achieved through the use of a thermostat and optimal management of this period, significantly reduce pollutant levels and have a positive effect on controlling engine emissions. These results emphasize the importance of employing optimized cooling systems to decrease pollution and improve the environmental performance of combustion engines.