There is described herein methods and systems for evaluating a condition of an engine. Fluid sample data obtained from an engine is received and weights are assigned to different data sets of the fluid sample data. The data sets correspond to one or more classes of materials into which particles of the fluid sample are sorted. A characterizing sample signature of the engine is generated based on the data sets. The sample signature is compared to a plurality of reference signatures obtained from reference engines belonging to a common family with the engine. A selection is made from the reference engines for those having a difference between a corresponding signature and the sample signature below a threshold. Historical engine data of the selected reference engines is output as a basis for evaluating the condition of the engine.