A key difference between lubricating oil and other fluids in a turbine is:

The key difference that sets lubricating oil apart from other fluids in a turbine is that it not only serves as a lubricant but can also play a role in the operation of the turbine. Lubricating oil is essential for reducing friction between moving parts, thereby minimizing wear and tear. Moreover, it helps in transferring heat away from critical components, which is important for maintaining optimal operating temperatures and ensuring the reliability of the turbine.

Unlike other fluids that may primarily serve a single purpose, the multifunctional capability of lubricating oil makes it integral to the efficient operation of a turbine. For instance, while some fluids might primarily serve as coolants or for other specific functions, lubricating oil's role is broader, enhancing both lubrication and cooling simultaneously.

The other options do not capture the primary distinction of lubricating oil in this context, as it doesn't solely serve for cooling, it does not decrease turbine efficiency—instead, it promotes efficiency by reducing friction, and it is indeed affected by temperature as its viscosity and performance can change with temperature variations. These characteristics align with its function in machinery like turbines, making it a unique and necessary fluid in such applications.