AVP uses this on their rebuild engines to tell if has been overheated or not.
 They are only dime sized things that look like a ring of metal with some wax
in the middle.  If the wax-like stuff melts out then your engine has run
hotter than they want.  I think one of these was on the base of the engine
(driver's side), on the head (under the intake on both sides) and maybe some
where else (its been a while).

The story behind how I know this:
AVP was trying to not pay a former list member his warranty claim on this
particular motor (not installed by me).  The motor was not overheated or
abused, but just failed because the cylinder walls wore away (I have never
seen anything like it before and AVP said neither had they).  The motor only
had 5k miles on it since rebuild so they did pay to have to shipped to them,
and rebuilt again, and shipped back, but I don't know if they ever paid for
my labor in Removing and Replacing the motor.  Haven't heard from the
customer since so I assume the motor is now doing well.

Hope this helps,
Ken Wilford
http://www.vanagain.com
John 3:16
Office (856)-765-1583
Shop (856)-327-0027
Fax   (856)-327-2242