In this paper, a convenient and rapid method is proposed for estimating the lubrication condition and characteristics at the piston–cylinder liner, where sliding motion similar to that like in a reciprocating engine occurs. In general, condition monitoring and diagnosis of the lubricant analyze density, type, form, and the chemical properties, including those of the wear particles. These conventional analysis methods are practical to use, have high reliability, and can often extract extensive information on the wear phenomenon. However, it takes a long time to analyze and assess the results. The proposed method is used to create a three-dimensional graph for the high-frequency vibration (termed sliding ultrasonic vibration) that results from direct contact of the sliding parts of the piston–cylinder liner. The theoretical oil film thickness and degree of contamination are obtained from the sampled lubricant. As a result, more efficient condition monitoring and diagnosis of the lubrication can be performed by applying the proposed method than with conventional methods.