Jay Honeck wrote:
The issue with shock cooling isn't the rate of cooling per se, but
rather stress induced by differential cooling.
Actually, I think it is the rate of cooling *and* the differential
cooling -- if it exists at all. Like you, I am skeptical -- but am I
willing to bet $25K on it? Nope.
How does the rate affect things? I have a masters in structural
engineering and work for a materials company so don't be afraid to get
technical. :-)

How 'bout this: It's the disparate rates of cooling in some parts of
the engine (versus others) that causes the differential cooling that
induces stress?

Yes, that is what I said originally. It is differential cooling that
causes the problem, not the rate of cooling itself. If you could cool
the entire engine uniformly, I don't think it would matter much how fast
you cooled it.

It isn't the rate itself that causes a problem, it is the difference in
rates from one location to another. However, I still think that the
greatest thermally induced stress occurs during the initial heat-up from
a cold start, but I don't have any data to confirm that and I don't have
an instrument airplane with which to collect the data.

Matt