Aircraft Systems

The oil temperature gauge measures the temperature of oil. Air cooling is accomplished by air flowing into the engine A green area shows the normal operating range, and the red compartment through openings in front of the engine line indicates the maximum allowable temperature. Unlike cowling. Baffles route this air over fins attached to the engine oil pressure, changes in oil temperature occur more slowly. cylinders, and other parts of the engine, where the air absorbs This is particularly noticeable after starting a cold engine, the engine heat. Expulsion of the hot air takes place through when it may take several minutes or longer for the gauge to one or more openings in the lower, aft portion of the engine show any increase in oil temperature. cowling. [Figure 7-19] Check oil temperature periodically during flight especially The outside air enters the engine compartment through an when operating in high or low ambient air temperature. inlet behind the propeller hub. Baffles direct it to the hottest High oil temperature indications may signal a plugged oil parts of the engine, primarily the cylinders, which have fins line, a low oil quantity, a blocked oil cooler, or a defective that increase the area exposed to the airflow. temperature gauge. Low oil temperature indications may signal improper oil viscosity during cold weather operations. The air cooling system is less effective during ground operations, takeoffs, go-arounds, and other periods of high- The oil filler cap and dipstick (for measuring the oil quantity) power, low-airspeed operation. Conversely, high-speed are usually accessible through a panel in the engine cowling. If descents provide excess air and can shock cool the engine, the quantity does not meet the manufacturer’s recommended subjecting it to abrupt temperature fluctuations. operating levels, oil should be added. The AFM/POH or placards near the access panel provide information about Operating the engine at higher than its designed temperature the correct oil type and weight, as well as the minimum and can cause loss of power, excessive oil consumption, and maximum oil quantity. [Figure 7-18] detonation. It will also lead to serious permanent damage, such as scoring the cylinder walls, damaging the pistons and Engine Cooling Systems rings, and burning and warping the valves. Monitoring the flight deck engine temperature instruments aids in avoiding The burning fuel within the cylinders produces intense high operating temperature. heat, most of which is expelled through the exhaust system. Much of the remaining heat, however, must be removed, or Under normal operating conditions in aircraft not equipped at least dissipated, to prevent the engine from overheating. with cowl flaps, the engine temperature can be controlled Otherwise, the extremely high engine temperatures can lead to loss of power, excessive oil consumption, detonation, and serious engine damage. While the oil system is vital to the internal cooling of the Cylinders engine, an additional method of cooling is necessary for the Baffle Air inlet engine’s external surface. Most small aircraft are air cooled, although some are liquid cooled. Baffle Fixed cowl opening Figure 7-18. Always check the engine oil level during the preflight Figure 7-19. Outside air aids in cooling the engine. inspection. 7-17