Oil testing – what does acid value mean?

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In oil testing, the acid value is almost always an essential parameter to measure, as it indicates the degree of oxidation and aging of the oil. In new oil, the additives are generally acidic; therefore, in the early stages, as these additives are consumed, the acid value shows a downward trend ； As usage time increases, under conditions of high temperature and high shear, the molecular chains of the oil break apart; under high compression conditions, they recombine, leading to the formation of acidic substances. As a result, the acid value tends to rise continuously. When it reaches a certain threshold, it can cause corrosion to the equipment, resulting in wear and damage. Therefore, we can take preventive maintenance measures based on the acid value, by filtering the oil or changing it as appropriate! In diesel engine oil, we generally test the alkalinity value rather than the acidity value, because diesel contains sulfur, and upon combustion it produces sulfuric acid-like substances that, when mixed with the oil, cause its acidity to rise rapidly. Therefore, diesel engine oils generally contain alkaline additives to neutralize the acidic substances produced by the combustion of diesel. That’s why we usually test the alkalinity value of diesel engine oils to determine the degree of oil degradation!