Cracked Heads :(
Thanks for pointing me to this thread. Some how I missed it in my search for coolant leaks. As you say, the verdict is still out.
If I understand the theory of the cracked head keeping the system pressurized, the cylinder with the crack would need to be compressed at shutdown to force gas into the cooling system and keep it pressurized above the cold state that it started on.
You also mentioned that building pressure fast is suspicious. How long should it take to fully pressurize the system?
'87 300TD 304kmi (RIP)
'95 Toyota Camry Wagon 125kmi