An oil sample analysis (OSA) evaluates the levels and types of metals and the presence of such contaminants as abrasives, soot, water, fuel, and engine coolant in the oil of gas and diesel engines. A lab report will flag any suspected anomalies, state possible causes, and offer some plain-English recommendations. Typical conditions that can be found by analysis include abnormal wear of metals, fuel dilution, dirt or water contamination, coolant contamination, and incorrect lubricant. Discovering any out-of-range condition early can prevent expensive repairs later on. For instance, fuel dilution will accelerate cylinder and bearing wear. High levels of solids will cause wear on bearings, pistons, cylinders, and the valve train. Excessive soot in a diesel engine can be caused by dirty injectors, weak ignition, low compression, or restricted intake or exhaust, among other things. Simply servicing a dirty injector can save an engine rebuild if caught in time.
Most OSAs will include the following:
- Spectral Exam: A spectrometer is used to find the quantity of various metals and additives in the sample — useful for finding excessive wear in bearings, pistons, rings, cylinders, valve train, and gears. It also determines the composition of any oil additives.
- Viscosity Test: The thickness of the oil at a specific temperature is tested — useful for finding fuel dilution, the breakdown of viscosity enhancers, or other contamination.
- Flash Point: Tests the temperature at which vapor from the oil ignites — contamination can cause a specific grade oil to flash higher or lower than the design flash point.
- Insolubles Test: Insolubles are typically abrasive solids — high readings are usually byproducts of incomplete combustion.
OSA is more useful as a tool to monitor a specific engine and/or transmission over time rather than as a one-time evaluation. Small changes, which may not look significant in a single analysis, will stand out if there are prior samples on record. For example, a higher lead or tin level than in past reports, while still within normal ranges, could alert you to accelerated plain bearing wear. That's not to say that OSA on a one-time basis isn't useful. A single sample (often performed in the course of a pre-purchase survey) will indicate a serious condition that deserves further investigation. However, a one-time analysis has to be carefully reviewed and interpreted prior to waving a red flag. The machinery total hours, type of machinery and use, type of oil and hours on the oil, knowledge of average baselines common to a particular unit—such context is important. This is where you may need the services of a knowledgeable marine-engine technician or surveyor; she can review the report in light of all known information, and then make recommendations.
I've found that many brokers dislike one-time samples because of questions that can arise due to lack of experience and the lack of a detailed service history typical of many vessels. The less knowledge there is about the sample taken, the broader the interpretation of the results must be. I recommend OSAs every year, more often for high-usage engines or for those that have red flags from previous analysis.