The test determines the viscosity class of the oil according to SAE (Society of Automotive Engineers) standards and makes it possible to check whether the oil maintains the required viscosity class or whether it has decreased. A drop in viscosity class can indicate the presence of fuel in the oil.
Combining the results of oil viscosity tests at 40°C and 100°C allows the viscosity index to be calculated.
Viscosity is usually determined at 40 and 100 °C, from which the viscosity index can be determined – a parameter describing the temperature dependence of oil viscosity.
Elements are divided into additives, impurities and wear elements. Additives may decrease as the oil is used. An increase in silicon levels in the context of contaminants can signal the presence of dirt or dust, suggesting that something is getting in from outside. The presence of potassium and sodium often indicates coolant getting into the oil. Wear elements, such as iron, chromium, tin or aluminium, can indicate wear and tear on engine components, whichever is present. Elemental testing can detect these problems at an early stage.
The wear parameter expressing the number of ferromagnetic particles, in combination with the study of non-ferromagnetic elements (e.g. copper and lead), allows additional interpretation of the analysis results.
The acid number directly indicates the content of acid products in the oil and is a parameter that determines the degree of ageing of the oil. An increase in the acid number indicates a higher amount of acid products, which indicates the progressive degradation of the oil. Acid products are formed by exposure to heat or oxygen from the air, forming carboxylic acids, aldehydes and ketones, among others.
The alkali number indicates the content of cleaning additives in the oil, such as detergents and dispersants. Its decrease indicates oil degradation. There is a correlation between the acid number, which increases as the oil is used, and the base number, which decreases. It is important that these ratios do not exceed each other – if the acid number exceeds the base number, this is a worrying signal that clearly indicates the need for an oil change.
The parameter I-pH correlates with the acid number and base number. A low acid number and low I-pH indicate a high amount of weak acids, while a high acid number and low I-pH indicate the presence of more strong acids.
This is an indication of the chemical purity of the oil. Each oil has its own characteristic spectrum. Here, we can determine ageing parameters, oxidation or glycol content (the presence of coolant in the oil).
The Karl Fischer method is the most accurate method for measuring water content, with up to 1,500 mg/kg being accepted as the norm, which corresponds to approximately 0.15% water in the oil.
The ignition temperature is the point at which the oil ignites when the ignition initiator is applied. Fresh oils typically exhibit an ignition temperature above 200°C, as the oil is used, this ignition temperature may decrease. A reduction in the oil’s flash point may indicate the presence of fuel in the oil.