Reciprocating Engine Cooling System Maintenance

in Lubrication and Cooling Systems

The engine cooling system of most reciprocating engines usually consists of the engine cowling, cylinder baffles, cylinder fins, and some use a type of cowl flaps. In addition to these major units, there are also some temperature-indicating systems, such as cylinder head temperature, oil temperature, and exhaust gas temperature. The cowling performs two functions:

  1. It streamlines the bulky engine to reduce drag.
  2. It forms an envelope around the engine that forces air to pass around and between the cylinders, absorbing the heat dissipated by the cylinder fins.

The cylinder bases are metal shields, designed and arranged to direct the flow of air evenly around all cylinders. This even distribution of air aids in preventing one or more cylinders from being excessively hotter than the others. The cylinder fins radiate heat from the cylinder walls and heads. As the air passes over the fins, it absorbs this heat, carries it away from the cylinder, and is exhausted overboard through the bottom rear of the cowl.

Figure 6-54. Small aircraft cowl flaps.

Figure 6-54. Small aircraft cowl flaps.

The controllable cowl flaps provide a means of decreasing or increasing the exit area at the rear of the engine cowling. [Figure 6-54] Closing the cowl flaps decreases the exit area, which effectively decreases the amount of air that can circulate over the cylinder fins. The decreased airflow cannot carry away as much heat; therefore, there is a tendency engine temperature tends to increase. Opening the cowl flaps makes the exit area larger. The flow of cooling air over the cylinders increases, absorbing more heat and the engine temperature tends to decrease. Good inspection and maintenance in the care of the engine cooling system aids in overall efficient and economical engine operation.