An engine is subject to greatest wear

• A. Cold start
• B. High altitude lean mixture
• C. High power settings with high altitude
• D. Lean cruise at cruise power

Answer: (A)

When the engine is cold, lubrication isn’t fully established and metal surfaces are tight against each other. The oil is thick and takes time to circulate to all bearings, and the oil pump hasn’t yet built up full pressure, so the protective oil film is thin or incomplete. That means increased metal‑to‑metal contact in moving parts like piston rings, cylinder walls, and bearings right at startup. Piston rings also haven’t seated and wear in most rapidly during this initial period. As the engine warms and the oil reaches normal temperature, viscosity falls and the oil film becomes more effective, reducing wear. Other operating conditions might stress the engine, but they don’t combine the lack of lubrication and cold metal that makes a cold start the point of greatest wear.