A thermostat mounted on the oil cooler controls the oil temperature by allowing some of the oil to flow through the cooler and another portion to flow directly into the oil supply tank. This arrangement allows the temperature to remain below65°C（150°F) of hot engine oil is mixed with the cold uncirculated oil in the tank. This increases the entire engine oil supply to operating temperature in a shorter period of time.

reciprocating engineDry thin oil lubricationsystem–Oil pressure regulating valve

The oil pressure regulating valve limits the oil pressure to a predetermined value depending on the installation situation. This valve is sometimes called a safety valve, but its actual function is to regulate oil pressure at the current pressure level.

The oil pressure is high enough to allow the engine and its accessories to be adequately lubricated at high speeds and power. This pressure helps maintain the oil film between the crankshaft journal and the bearing. However, the pressure cannot be too high, otherwise it may cause leakage and damage to the oil system. Oil pressure is usually adjusted by loosening the locknut and turning the adjusting screw.

On most aircraft engines, turning the screw clockwise increases the tension of the spring that holds the valve on its seat and increases oil pressure. Turning the adjustment screw counterclockwise reduces spring tension and reduces pressure. Some engines use washers under the springs that are removed or added to adjust the regulator valve and pressure. Oil pressure should only be adjusted after the engine oil is at operating temperature and the correct viscosity has been verified. The applicable manufacturer's instructions contain the exact steps for adjusting oil pressure and factors involved in changing the oil pressure setting.