Cessna 152 POH Practice Exam 2026 – Your All-in-One Guide to Mastering the Pilot's Operating Handbook!

Oil viscosity selection is about balancing lubrication during cold starts with film strength when the engine is hot. At a modest ambient temperature like 25°C, you want a viscosity that isn’t too thin for the hot operating conditions and not too thick when the engine first starts.

SAE 50 is the best choice here because it provides a robust oil film for normal Lycoming engine operation once the oil warms up, while still delivering adequate flow when the engine is starting in that 25°C environment. Too-light a viscosity would risk insufficient film during hot operations, leading to more wear; too-heavy a viscosity would place extra load on the starter and oil pump and hinder flow during startup.

The other options don’t fit this balance as well. A thinner grade would be more prone to thinning too much once the engine heats up, and a thicker grade would make starting and cold-flow performance more difficult. So for a 25°C outside air temperature, SAE 50 gives the appropriate balance for typical operation.