Oil oxidises over time and becomes more acidic indicating the age of the oil. If the oil is too acidic it can damage metal components and further accelerate the ageing process.
A rapid increase in the Acid Number may be due to:
- Severe oxidation (often caused by overheating)
- Depletion of additive package
- Top up with a large volume of incorrect oil with a much higher base acidity e.g. hydraulic oil
- Contamination with process fluids; or in case of engine oils with combustion products