Morgans wrote:
"Matt Whiting" wrote

The issue with shock cooling isn't the rate of cooling per se, but rather
stress induced by differential cooling. Most engines see far higher
temperature differentials during start-up than they do during cooldown.
Jay, have you timed your engine heat up rate? It would be interesting to
watch how fast your engine heats up from say a 50 degree cold start and
then compare that to the cool-down rate when you pull the throttle for
engine out practice. I'm assuming this would be fairly trivial with your
engine analyzer.

I'm pretty sure that the rate of heating of the metal of the head is not
the big issue, according to the shock cooling proponents.

Instead, it is the heads (and cylinders) cooling more rapidly than the
pistons, and the hot pistons (not able to be cooled as rapidly) against the
cooler cylinders (the cylinders do not have heat instrumentation, so the
closest thing they can do is to measure is the head temperatures) causing a
reduction in the tolerances between the piston and the cylinder walls, thus
causing possible scuffing and abnormal wear.

At least that is my take on what they say.

It seems to me that upon engine start the pistons would heat up much
faster than the cylinders causing the same net affect as cooling down
the cylinders faster once hot. Either way the pistons are hotter than
the cylinders.


Matt