1.Bluegreen Coolant: VAG G11 (TL 774 C) and is BMW approved. It is free of amin-, nitrit- and phostphates

2. Pink Coolant: VAG G12 (TL 774 D), Mercedes-Benz MB 325.3, MAN 324 SNF. G12 contains organic components and is free of nitrit-, nitrat-, phosphate-, amin- und silikates. In use at VAG since ca. 1997.

3. Purple/Pink colored Coolant: G12 plus (TL 774 F) which can be mixed with G11

When adding coolant, make sure you check ythe existing fluid or drain properly. It makes sense using demineralised water and compressed air to flush the heater core and radiator too as 30% of the coolant will be stuck there.

Never mix G11 und G12 coolant!  Mixing the two coolants causes problems because you get saturation of the silicates and gelling inside the engine, thus the specific ritual flush with water and compressed air.

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O.K., now my opinion about this G11 to G12 changeover. In order to understand this better, I'll tell you what I know about coolant.

Buy only high quality antifreeze-cheap brands can be straight ethylene glycol minus important corrosion inhibitors and lubricants. ALWAYS mix 50/50 with water(preferably distilled) or follow ratio recommend for your climate. Never top off coolant tank with straight coolant-preferrably small amount of distilled water or your 50/50 mixture. Use common sense, large amount missing means that if you refill, you are going to throw off the glycol to water ratio, and it is very important. Antifreeze should never exceed 65%. Exceeding 85% will cause the silicates to drop out of suspension and goo up to clog the radiator and reduce heat transfer. VW recommends the water and compressed air treatment to upgrade to G12 because up to a third of the coolant is still trapped in the heater core and the engine after you pull a hose or the drain cock. This flush ensures that you are removing all accumulated rust, scale,silicate buildup and old coolant as best as possible. By the way, the blue and red coolant will foam up and turn
brown in your expansion tank if you mix them or don't get all the G11out.

The degree of corrosion that takes place in your VW depends upon the type of minerals and alloys in the engine and radiator, and the acidity or alkalinity of the coolant. So long as your coolant remains alkaline, corrosion will be held to a minimum. Conversely, acidic coolant hastens the corrosion process that occurs between the cast iron and the aluminum present in the engine and radiator. The corrosion inhibiting chemicals that are added to you coolant is what keeps the alkalinity on the high side of the Ph scale. That's why adding aftermarket wetters and boosters is not smart because you are altering the already unknown alkalinity of your coolant(no matter how new, it varies depending on mix ratio, mineral content, additive content) More important, this alkalinity ratio doesn't have to be bigger to be better-it just needs staying power. This is measured as alkalinity reserve(how long your coolant can resist corrosion) The enemies of your coolant are heat, dissolved oxygen and minerals which react with the metal surfaces in your engine depleting the capacity of the coolant to resist becoming acidic. Therefore, changing the coolant annually or at least bi-annually guarantees that you never exceed the coolants ability to resist corrosion. European car makers like VW specify coolant additives lacking in phosphates and including borates and low silicates because their water is harder and it reacts with phosphates to create calcium and magnesium deposits. The Japanese disagree and specify high in phosphates and low in borates and silicates because they fear lack of maintenance will cause borate corrosion. This is the reason you see the little "phosphate free coolant " only from vw under the expansion tank cap-or it will void mf's warranty. It seems that in my opinion, the original G11 coolant must have been a poor acidic retardant-either from the reaction to the water installed from the factory and/or an additive package that was insufficient to go more than a couple of years on North American water. Mixing the two coolants causes problems because you get saturation of the silicates and gelling inside the engine, thus the specific ritual flush with water and compressed air.

I firmly believe that no matter what proportion VW used for an additives package with the G12 coolant, it too should be flushed out and refilled every year or two. Considering that it isn't that much work and it beats playing with litmus paper and rebuilding your cylinder head. By the way, the corrosion we usually see on VR6s is surface etching that rubs away to leave pits-almost always around any flange that attaches to the head, or on the water jack inlets comprising the head gasket. They're usually good to go because they are far enough away from critical sealing areas, but we do replace heads when they are questionable. I really doubt that the new metal gasket is the reason for the G12. There is actually no bare metal on the gasket and all the passages have sealer from the factory around them. I think the reason was simply that G11 didn't provide long enough reserve capacity and coupled with poor maintenance, they were getting too many warranty problems.