An oil analysis can help determine engine health, but only if you know what to look for. This video from Engineering Explained (and sponsored by Mobil 1) breaks it all down.
Host Jason Fenske used his own Subaru Crosstrek for this explainer, taking 12 synthetic oil samples and sending them in for analysis. That included four samples of new oil, four samples taken after 15 minutes of idling post oil change, and four samples taken following a 3,000-mile road trip. One set was sent to Mobil 1, but because Mobile 1 also sponsored the video, Fenske also sent a set to Blackstone Laboratories for verification (the third set was a back-up).
Oil analysis can produce a lot of information. A good place to start wading through that information is looking at wear indicators, such as various metals that could indicate engine wear if they show up in the oil in significant quantities. The presence of different metals, expressed in parts per million (ppm), can be used to gauge the health of different components, such as aluminum for pistons, or iron for the crankshaft, since the metal is being shed by those respective components and deposited in the oil.
The analysis also shows contaminants. Potassium and sodium are byproducts of engine coolant, so seeing noticeable amounts in the oil indicates coolant is mixing with the oil, which could point to a head gasket failure. Silicon could indicate contamination from sand or dirt from a nonfunctioning air filter.
Oil analysis can also indicate the health of the oil itself, and whether it’s time to change it. Fuel dilution is an important factor here, as fuel mixing with the oil can thin it out and make it less effective. So is the Total Base Number (TBN), which basically shows the level of additives that fight the buildup of contaminants (the third-party lab used for this test recommends a TBN above 1.0).
Analysis can also look at soot (more of a concern in diesel engines and direct-injected gasoline engines) and water contamination, viscosity levels, and the level of oxidation and nitration—two chemical reactions that degrade the oil over time. If you change your oil at the factory-recommended intervals, though, you’re unlikely to see anything unusual here.
