Shock cooling

Manifestation

Damage from shock cooling is most commonly believed to manifest itself as stuck valves, excessively worn or cracked pistons and cracked cylinders and cylinder heads.

Analysis

While the subject is very controversial, some believe shock cooling, as commonly explained, is nothing but a myth. This position is supported by the fact twin engine planes commonly experience ideal conditions for shock cooling during simulated, single engine failures, yet statistically show no difference in wear or damage probability distribution between engines. Doubts have been raised regarding the plausibility of achieving the temperature reduction in cylinder heads during flight that is purported to cause damage in most engines. Equally, it has been pointed out the rate cylinder head temperatures drop off after a normal engine shutdown is often much faster than the usual rates deemed to present a shock cooling risk. Complicating the analysis, high operating temperatures in and of themselves can contribute to excessive component wear and damage, which is typically associated with "shock cooling".

Detection and prevention

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. Spoilers on the wings may also be deployed to lose lift without having to reduce engine power substantially, slowing the rate of engine cooling.

References

1. (19 February 1997). "Shock Cooling: Myth or Reality?".
2. "How to Avoid Sudden Cooling of Your Engine".
3. (5 November 1996). "Shock Therapy".
4. (4 January 2018). "Shock Cooling: Time To Kill The Myth".