Customers need to know when an engine oil should be changed and they rely on us to detect early stage problems with the engines themselves. Client owners of heavy duty engines commonly ask us several questions about their vehicles: is my additive package still effective? Do the viscosity and the viscosity index indicate that the lubricant remains acceptable for enduring periods of runtime? What is causing the oil viscosity to change, and why are these new contaminants and metals present in the oil when they previously were not? We answer these questions, with the goal to extend the use of the oil when appropriate and detect early stage degradation of the lubricated equipment.