This is a grey area. It all depends on what the factory/dealer put in there first.Some anti freezes wont mix.
I copy/pasted this from another forum so as to avoid all the BS that was in the rest of the thread...
There are three basic types of ethylene glycol coolant.
1. Conventional/traditional
2. OAT organic additive (acid) technology
3. HOAT (Hbrid OAT with silicates)
They are all available in every color you can imagine.
HOAT are further divided into parially formulated (requires
a supplement for diesel applications) and fully formulated
can be used as is in diesel applications. The fully
formulated can be substituted for partially formulated. The
addition of silicates provides fast acting protection that
OAT coolants lack and provide a barier that protects
plastics from potential deplymerization of some plastics.
Fully formulated HOAT Examples: Zerex G-05, Chevron Custom
Made, Texaco/Havoline Custom Made, Motorcraft Premium Gold,
Mercedes Benz, Freightliner Purple long life, Mopar Long
Life Orange, Mopar Long Life Gold/Amber, Peak CF-EXL, MTU
Green.
Partially Formulated Examples: VW Blue, BMW Blue, Volvo
Green, Zerex/Glysantin/BASF G-48 (Saab and others have used
this also. If it's Blue and European OEM, It's G-48).
OAT comes in many varieties. The Japanese have high
phosphate versions and a few molybdate versions. Molybdates
improve water pump protection. European and American
versions are phosphate free. GM and others that are "GM
Dexcool approved" and some "one size fits all" versions use
a specific 2-EH acid that some OEMs believe cause problems
and are dead set against. European and American versions are
usually phosphate-free. All are silicate free.
Toyota uses a couple of non 2-EH versions with molybdates
for extra cavitation protection.
Peak Global is a non-2-EH version.
Most European red/pink coolants are Zerex/Glysantine/BASF
G-30. VW/Audi/porsche, Jaguar and others use it and have
used it.
GM/AC-Delco/Shell/Chevron/Texaco/Havoline is the 2-EH
Dexcool stuff and Zerex/Gysantine G-34/Extreme Life 5/150 is
the European Dexcool (Newer Saab etc) with molybdates.
Conventional coolants come in passenger car (ASTM D3306)
partially formulated HD (accepts supplements for HD service)
and fully formulated (Ready for HD service). All include
silicates for fast acting protection against abrasives and
water pump cavitation. Supplements to address HD cylinder
liner cavitation include the SCA/DCA-2 nitrite stuff and the
DCA-4 molybdate/nitrite stuff.
Silicates can cause problems in some cars Phosphates can
cause problems in some cars 2-EH acids can cause problems in
some cars Borates can cause problems in some cars Silicates
are required in some cars 2-EH acids are required in some
cars
There is no such thing as a one size fits all coolant.
You have to know what's in there before topping it off. Let some of the others chime in...