>
> >Paul Cavanaugh wrote:
> >
> >>  Well, the mystery continues...
> >>
> >>  My mechanic tested the coolant (while the engine was both hot and
> >>  cold) for traces of combustion leakage (hydrocarbons in the cooling
> >>  system) and found nothing.
> >>
> >>  He also found no excessive pressure in the oooling system (I replaced
> >>  the expansion tank pressure cap 2 weeks ago, just to be safe).

I am quite certain that your problem was caused by a bad pressure cap that was
not releasing when it should.  With a working pressure cap, the pressure
should never build up high enough to cause the repeated damage you describe.
  It is logical that there is no excessive pressure now if you have recently
replaced the cap.

Larry A.