Abstarct: Checking the instantaneous state cary out for the internal combustion engine oil to ensure the lubricant's protective function and engine health. The purpose of present study is design and manufacturing capacitive sensor for online oil quality monitoring sensor. Noise factors such as temperature, pressure and oil discharge were investigated on sensor performance. The effects of various oil deterioration factors such as water pollution, fuel contamination and oxidation on the sensor outputs in the hydraulic circuit were online. In addition, the sensor was evaluated in real operating conditions in both investigated Inside the circuit online and offline durability tests. The geometry of the electrodes of this capacitive sensor is designed to increase its capacitive capacitance, which by increase of capacitive capacitance the oil changes measuring more precise manner and the presence of bubbles in the oil not affecting in the measurement. The oil passes through this capacitive sensor, which allows online monitoring of the oil pressure difference between the input and output, and, in the case of oil discharge control, oil viscosity can be monitored. The advantages of this design are better oil flow, lack of deposition within the sensor and consequently increased accuracy in detecting oil defects and detecting gasoline contamination in the oil. Sensor outputs, capacitive capacitance, theta angle (the ratio between the imaginary part and the actual part of permittivity), the difference in pressure between the two sides sensor and the oil temperature, that the different causes of oil degradation have different effects on each one. The results of the tests indicate that the sensor is capable of detecting various oil defects such as water pollution, fuel pollution, and oxidation, so that a specific range of sensor outputs for oil health can be determined.The low cost of production and the simple and online processing of sensor data output and high accuracy are the oil quality sensor features.