🔍 Key Concepts

• Effect of fuel dilution on lubricating oil properties in diesel engines • Relationship between viscosity and pressure in a lube oil system with a positive-displacement pump • How contamination changes lubricating film strength and bearing protection

💭 Think About

• Think about what happens to the thickness and flow characteristics of lube oil when a lighter fuel oil gets mixed into it. • Consider how a constant-speed, positive-displacement lube oil pump will respond if the oil becomes thinner instead of thicker. • Ask yourself which choice describes a realistic system reaction to thinner, less viscous lube oil: does pressure tend to go up or down?

✅ Before You Answer

• Verify whether fuel oil is lighter or heavier (in viscosity) than normal lube oil used in diesel engines. • Check what happens to system pressure in a lube oil system if the oil viscosity decreases while pump speed stays the same. • Eliminate any answer choice that implies thicker oil or greater resistance to flow when fuel is added to lube oil.