🔍 Key Concepts

• heat patterns on piston rings in a properly lubricated diesel engine • relationship between shiny vs. black (carbon-coated) surfaces and where the ring contacts metal or combustion gases • which ring surfaces actually rub against the cylinder wall during normal operation

💭 Think About

• Think about which part of the compression ring is in constant sliding contact with the cylinder liner and how that contact will affect its appearance. • Consider where combustion gases and carbon deposits are most likely to accumulate on a ring that is sealing properly. • Ask yourself: if the engine is efficiently operating and lubrication is good, which surfaces will be clean and polished vs. which will be dark or sooty?

✅ Before You Answer

• Identify which ring surfaces are bearing and sealing surfaces against the liner (these tend to become polished or shiny). • Identify which surfaces are more exposed to combustion gases and carbon without heavy wiping contact (these tend to become dark/black). • Before choosing, make sure your option matches a pattern where the primary rubbing surface is clean/polished and the more gas-exposed, non-rubbing surfaces are darker.