Exam Question

### **1. Reasons for Close Control of Lubricating Oil Temperature (8 Marks)**
Close control of lubricating oil (L.O.) temperature supplied to a marine diesel engine is paramount for engine reliability, efficiency, and longevity. The optimal temperature range is typically between 45°C and 55°C. Deviations from this range can have severe consequences:
* **Viscosity Maintenance:** Viscosity is the most critical property of lubricating oil and is highly dependent on temperature.
* **High Temperature:** If the oil temperature is too high, its viscosity decreases significantly. This thins the oil film, reducing its load-carrying capacity. The result is a transition from hydrodynamic to boundary lubrication in bearings (main, crosshead, bottom end) and other moving parts. This leads to increased friction, accelerated wear, and potential for bearing metal wiping or seizure.