Question 11 OSE01 - Chief Engineer - OSV

The Correct Answer is C **2. Explanation of why option C is correct:** Option C ("An unusual drop in viscosity indicates excessive dilution of the lubricating oil with diesel fuel oil and an unusual rise in viscosity indicates excessive oxidation of the lubricating oil.") correctly identifies the standard physical effects of these two major degradation issues: * **Viscosity Drop and Fuel Dilution:** Diesel fuel oil (DO/MGO) is inherently much thinner and less viscous than engine lubricating oil. When fuel leaks or mixes into the lube oil system (dilution), it lowers the overall viscosity of the mixture, resulting in an unusual **drop** in the viscosity reading. * **Viscosity Rise and Oxidation:** Excessive oxidation or thermal degradation occurs when the oil breaks down due to heat and exposure to oxygen. This process causes the formation of sludge, varnish, and high-molecular-weight products (polymerization). These larger, heavier molecules increase the internal friction and resistance to flow, leading to an unusual **rise** in the viscosity reading. **3. Explanation of why the other options are incorrect:** * **A) Incorrect:** This option states that a *rise* in viscosity indicates excessive dilution. This is false. Dilution (mixing a thinner fluid like fuel with the oil) always causes a *drop* in viscosity. * **B) Incorrect:** This option incorrectly links an unusual *drop* in viscosity to excessive oxidation (oxidation causes a *rise*). It also incorrectly links an unusual *rise* in viscosity to excessive dilution (dilution causes a *drop*). * **D) Incorrect:** This option states that an unusual *drop* in viscosity indicates excessive oxidation. This is false. Oxidation creates heavier molecules that *increase* viscosity. While a drop in viscosity does indicate dilution, linking it to oxidation (which causes a rise) makes the statement fundamentally misleading regarding the causes of viscosity changes.