Matt Barrow schrieb:

You're worrying about virtually nothing!
http://www.avweb.com/news/maint/182883-1.html

Shock Cooling: Myth or Reality?

Powerplant management guru Kas Thomas of TBO ADVISOR examines the physics
and metallurgy of "shock cooling" and concludes that, contrary to the
conventional wisdom, it is not a major contributor to cylinder head
cracking.

Lycoming says otherwise:
http://www.lycoming.textron.com/supp...Operations.pdf

Lycoming
Sudden cooling is detrimental to the good health of the piston aircraft
engine. Lycoming Service Instruction 1094D recommends a maximum
temperature change of 50° F per minute to avoid shock-cooling of the
cylinders.

Operations that tend to induce rapid engine cooldown are
often associated with a fast letdown and return to the field after
dropping parachutists or a glider tow. There are occasions when Air
Traffic Control also calls for fast descents that may lead to sudden
cooling.

The engine problems that may be expected when pilots consistently
make fast letdowns with little or no power include:

1. Excessively worn ring grooves accompanied by broken rings.
2. Cracked cylinder heads.
3. Warped exhaust valves.
4. Bent pushrods.
5. Spark plug fouling.
/Lycoming


Be aware that "powerplant management guru Kas Thomas" won't buy you a
new engine if you happen do damage yours by following his recomendations.

It's every operator's choice whether he prefers to believe the engine
manufactorer or some guru.

Stefan