Which cylinder in a four-cylinder inline air-cooled engine is the coolest while running?

In a four-cylinder inline air-cooled engine, the first cylinder is typically the coolest due to its position at the front of the engine and its exposure to airflow. As the engine operates, air is drawn in from the front and flows over the cylinders. The first cylinder benefits from this direct airflow, allowing it to dissipate heat more effectively than the others, especially when the engine is in motion.

Furthermore, the arrangement of the cylinders means that as heat is generated from combustion and dissipated, the cylinders further back (2, 3, and 4) are subjected to the heat radiating from the cylinders in front of them. This cumulative heat buildup can contribute to their higher temperatures. Additionally, as heat rises and the coolant flow may not always be as direct to the rear cylinders, it can further isolate those cylinders from efficient cooling.

As a result, the first cylinder, by virtue of its positioning and airflow, typically maintains a lower operating temperature compared to the others, making it the coolest cylinder in the engine while running.