When should an oil sample be collected?

Collecting an oil sample mid-stream during an oil change is the best practice because it provides the most representative sample of the oil in the system. At this stage, the oil is being drawn from the engine while it is still circulating, which helps to capture any contaminants or wear particles that may be present suspending in the oil. This approach increases the accuracy of the analysis, as it reflects the true condition of the oil and engine wear over time.

Taking an oil sample only when necessary or when a failure occurs may result in missing critical information about the engine's health prior to failure. Additionally, collecting a sample as soon as the drain plug is removed may not yield a representative sample, as any settling contaminants may not be included in the sample, skewing the results and providing a less accurate assessment of the engine’s condition.