In a message dated 1/27/00 10:12:43 AM Pacific Standard Time,
stuart@COBALTGROUP.COM writes:

<< They mix fine, but if the Prestone is supposed to be five year, 50,000
 mile "new technology" coolant, it won't last any longer than the regular
 stuff if there is more than 10% of it in the mix.

 It is best to stick with one brand since the corrosion inhibitor
 additive packages are all a bit different, and there is no guarantee
 that mixing brands won't reduce corrosion protection.
  >>

The correct answer is to never mix the coolant unless it's exactly the same.
The factory pink stuff is forever coolant. It never requires changing. If
topping it off, it only requires water. If adding VW pink stuff, don't forget
you need to pre mix the coolant with 50% water and 50% coolant. Never ever
mix the old VW blue coolant with the VW pink coolant. Many tech bulletins
have been issued from VW to never do it.
 See ya, Michael
 87 syncro
 87 quattro