Modern diesel engine maintenance programs incorporate various methods and techniques for early fault detection and diagnosis to maintain efficiency, low pollution and high reliability and to avoid catastrophic failures. This study has been conducted aiming at engine oil condition monitoring and quality evaluation by analysing the engine block vibration and its induced noise. The vibration signals were measured using an accelerometer mounted on the thrust side of the first cylinder in a four cylinder diesel engine, and the noise was recorded using a microphone facing the cylinder. The signals are then band pass filtered and transformed to the frequency domain, where the amplitudes of the different frequency components of the vibration and noise waveforms are analysed and compared to the vibration and noise baseline signatures. The mean amplitudes of the spectral components in the frequency band 900 Hz to 2.5 kHz were found linearly proportional to the engine speed and load. It was also found that the RMS values of this frequency band are affected by the oil viscosity. These results show that it is possible to use vibration and airborne acoustics to predict the quality of lubrication.

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