Shock cooling (engines)
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Shock cooling refers to the theory that damage to engines (particularly air-cooled aviation piston engines) may occur because of an excessively rapid decrease in temperature.
The situation where rapid cooling arises is on descent from altitude. In this condition, less power is demanded of the engine (it is throttled back) so it is developing much less heat. In a descent, the plane's airspeed increases, simultaneously increasing the cooling rate of the engine. As metals expand and contract under temperature changes, dimensional changes in the engine may exceed tolerance limits.
Damage from shock cooling most commonly manifest itself as stuck valves [1] and some have attributed cracked cylinders to shock cooling as well.
A single cylinder head temperature (CHT) sensor, or in more sophisticated installations, an array of sensors (one for each cylinder) may be employed to monitor the temperature and cooling rate of the engine, usually through a simple gauge or a bar-graph style graphical display. Spoilers on the wings may also be deployed to lose lift without having to reduce engine power substantially.
Kas Thomas, a respected aviation engine expert, believes that "shock-cooling is not a major contributor to cylinder head cracking".
