What be the problem with switching from the old green coolant which has the silicate/ phosphate etc to the newer acid based coolants, such as amsoil  poly organic acid technology.  The car is over 20 years old.  Of course I would clean out the old coolant.

I just wonder if anyone actually has done this.  Of course, the mgfs say that the new coolant is compatible, etc.

Bump.  Surely someone has put the newer organic acid based antifreeze in their old subaru.  I'm worried that it will peal off the scale and plug up the heater/radiator..

nope, sorry, have not & don't see a need to. The car does not call for it, so why would I go to the added expense of something that could potentially cause harm?