Definition
The application of external heat to a piston aircraft engine before starting in cold weather, used to warm the engine block, oil, and internal components so that oil can flow properly and the engine can start without damage.
Plain English
Warming up the engine from the outside before you try to start it, so the cold oil can move and the engine parts are not stiff or brittle when they begin to turn.
Context Anchor
Seen during cold-weather preflight and engine starting procedures, especially when the airplane has been parked outside in low temperatures.
Derivation
From 'pre-' (before) and 'heat.' The word simply means heating something before it is used. The aviation point is that this heating happens before the start sequence, not after.
Why Pilots Care
Starting a cold engine without preheat can cause oil starvation and mechanical damage during the first moments of operation.
Grounding Statement
On a freezing morning, engine preheat gives the engine a warmer, easier start before the starter turns it.
Intuition Check
Engine preheat does not mean letting the engine idle for a long time after it starts. It means warming the engine before the start, using a safe method approved for that airplane.
Example Sentence 1
With the temperature at minus ten degrees Celsius overnight, the pilot arranged an engine preheat before the morning departure.
Example Sentence 2
In sub-freezing conditions the instructor reminded the student to apply engine preheat before attempting the first start of the day.