🔍 Key Concepts

• Purpose of lube oil in turbine bearings (cooling AND lubrication) • Typical operating temperature range where oil viscosity is still high enough to protect bearings but warm enough to flow easily • Effect of too cold vs too hot oil on bearing performance and machinery clearances

💭 Think About

• Think about which temperature range keeps the oil thin enough to circulate easily but still thick enough to form a protective film on fast‑rotating turbine bearings. • Eliminate any choices that are closer to room temperature drinking water and any that are so hot they might begin to reduce oil life or risk varnish formation. • Consider what temperature range you’ve seen in engineering logs for main turbine lube oil supply—not sump temperature, but supply to the bearings.

✅ Before You Answer

• Compare each choice to a normal machinery space ambient temperature and ask if it makes sense for lube oil to be just barely above that, or significantly warmer. • Recall that most turbine bearing lube oil systems use heaters and coolers to keep oil in a fairly narrow band, typically somewhere in the warm but not hot range. • Verify in your notes or references what is considered a typical lube oil supply temp for high‑speed rotating machinery, not diesel engine jacket water.