[...]
straight from Prestone  is  Do Not mix green and orange types.
Something about the two together can cause corrosion problems.  They
say to flush the system thoroughly before changing types.  They do  say
that you can change forward ie  green to orange but to check with your
oem for the car before going back from orange to green.
from VW tech shop locally
vw from about 1992 to 1997 is blue or green(thinks it may have depended
on the origin of the vehicle) but was low phosphate.
1997 and up vw is red  the red is basically the "environmentally
friendly" solution
blue is basically the same as the new "orange"
VW emphasizes phosphate free for vanagons and corrosion as one of
causes of problems with the cooling systems on those vehicles.
He did state that in buying your coolant you have to read the labels
closely.   Generally but not alway, the higher priced brand will have
less phosphate.
As prestone said do not mix and thoroughly flush, VW master tech
emphasized the same if going from red to blue.  also said  if going
backwards  with VW  you should not have any problems but didnt
recommend it as there may be long term results that he hadnt seen yet.
jimt
On Thursday, September 12, 2002, at 09:55 AM, gary hradek wrote:

> The color is added to the coolant more to identify the
> product manufacturer and it tells you very little
> about what it is or is not.   It is true that most
> phophate containing coolant is green and mixing
> different color coolant in the short term will not
> make too much difference. Green is often the cheapest
> stuff and the easiest to locate.  Mixing one color
> with another color will shorten the life span of the
> long term coolant if one color is not long term.
> Most important thing is to change the coolant to