Viscosity values may increase or decrease during operation. In fact, in the automotive industry, monitoring the viscosity of lubricants is considered a principal indicator of oil quality. It is then particularly important to monitor the properties of oil especially, as its degradation can eventually lead to engine damage or failure. High temperature solid impurities (such as soot, coke, products of tribological wear of the engine, corrosion products, etc.) and the external ones (moisture, air dust, air, and other gases), as well as shear, oxidation, and nitration processes are some of the key factors contributing to the degradation of engine oil. The study fills an important gap in empirical research in the context of the reliability of measurement results obtained using various research techniques.Įngine oil ensures smooth engine operation through its lubricating and cooling effects yet, with time and use, it becomes subject to degradation processes. Therefore, a very careful approach is suggested when choosing these instruments. It was also found that the results obtained with the use of the mid-FTIR spectrophotometer were burdened with a very large measurement error.
Consistent outcomes were obtained for the Stabinger viscometer only, whereas the microchannel viscometer and the mid-FTIR spectrophotometer were not as precise as the reference method. The main data analysis tools used in the study were multiple regression, Mahala Nobis distance, post-hoc analysis, and the Wilcoxon signed-rank test with the Bonferroni correction. The study material comprised 42 fresh engine oils, all of which are commercially available. The following instruments were selected to measure: a mid-FTIR spectrophotometer, a microchannel viscometer, and a Stabinger viscometer. The aim of this paper is to compare the results of kinematic viscosity of lubricating oils measurements at 40 ☌, obtained with three different rapid evaluation devices, and the standardized method using an Ubbelohde Capillary viscometer.
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