The Analysis of New and Used Motor Oils

Abstract

Differentiation of motor oil samples could assist in crimes such as hit and runs and any other scene where oil was present. Currently there is not a lot of research available on the differentiation of oil. Some papers have suggests that it is possible to differentiate between new oil samples and used oil samples 1-3. Thirty-nine samples of new oil were analysed using gas chromatograph-mass spectrometry. When compared visually and statistically, using smoothing and principal component analysis, variation could be seen between each sample. Sample that had the same grade were the most similar, oil samples of different grades could easily be differentiated from each other. Selected ion monitoring was carried out on some new oil samples. The result could differentiate between oil samples but provided little additional information. Samples of oil were taken from eighteen different vehicles. Samples were taken from the dipstick of the vehicle and the sump. These samples were then compared using the same method as with the new oil samples. The oil samples from the dipstick could be differentiated from each other. Only four cars had detectable oil on the sump. The samples taken from the sumps of vehicles looked very different to the same taken from the dipstick of the same car. Samples were collected from two cars over a period of time when the vehicles had travelled set distances since new oil had been put in the engine. There was very little variation between all the samples suggesting that the oil in the engine did not change over time. However, the cars used very new and an older engine may have more of an effect on the oil. The results indicated that the differentiation of oil may be applicable to casework and with further research could be a promising tool in crimes where motor oils are present.