🔍 Key Concepts

• Effect of diesel fuel mixing with crankcase lube oil • Meaning of viscosity and why it matters for bearing protection • Typical causes of bearing failure, sludge, and acid formation in lube oil

💭 Think About

• Ask yourself: if a thin liquid (like diesel fuel) mixes with a thicker lubricating oil, what happens to the overall thickness (viscosity) of the mixture? • Which of these options describes a direct and immediate effect of fuel getting into the crankcase, rather than a long-term secondary result? • Consider what usually causes sulfuric acid formation in engines — is it primarily from fuel dilution, or from combustion byproducts combining with moisture?

✅ Before You Answer

• Compare the thickness of diesel fuel vs. lube oil and think how mixing them changes the oil’s protective film. • Identify which choice describes a chemical reaction (like acid formation) versus a physical change (like thinning). • Eliminate any answers that are more likely to be downstream consequences of poor lubrication rather than the first direct effect of fuel entering the crankcase.