Methods for detecting oil conditions including a top level of an oil in an oil system which is reduced to a top level of a predetermined threshold amount of the oil, a normal oil deterioration which occurs in the absence of water having a confirmed actual remaining usage of the oil, and an abnormal oil deterioration which occurs in the presence of water. The methods include a first preferred embodiment which applies reference and sensing capacitors to obtain a measured temperature compensated electrical property of the oil. From which a quantitatively measured remaining usage is obtained so as to a predicted one for the oil. Therefore, the respective top oil level, or the normal or the abnormal oil deterioration can be concluded according to the measured remaining usage which is respectively larger than, or similar to, or less than the predicted one for the oil. A second preferred embodiment only includes the sensing capacitor for obtaining the measured temperature compensated electrical property of the oil. Variations to the embodiments lead to application of at least two sensing capacitors to monitor an uneven distribution of the oil deterioration or a full range of the level of the oil in the entire oil system.