^^^This^^^^

 

This is not accurate information.

Mixing Prestone's current extended life formula with G12 will not cause your coolant to suddenly turn to sludge. It will turn the coolant brown, but that is simply due to the mixing of the green and pink dyes. This is an argument as old as the debate of mixing conventional and synthetic oil. Both G12 and Prestone's extended life coolant are both Ethylene Glycol-based.

G12 Coolant MSDS: http://www.sunoco.be/PDF/UK/MSDSUKAntifreeze%20G12.PDF

Prestone Coolant MSDS: http://www.nukaresearch.com/projects...tifreezeEG.pdf


Certain aftermarket coolant may, however, be incompatible with certain parts specified by Audi in the cooling system due to a lack of certain additives. This may lead to premature failure of seals or hoses, but will not cause gelling. Sludge buildup is due to lime deposits and high acidity, which is caused by failed coolant and can occur with ANY type of coolant used if the owner is neglectful of the vehicle's coolant system maintenance.

Aftermarket EG coolants generally last 1-2 years. After that the coolant turns acidic and can cause build-up in the coolant system, causing multiple leaks and blockages. G12 is designed to last about 5 years, but mixing it with aftermarket coolants can cause the life expectancy to drop to 1-2 years. Leaving it in there any longer causes issues. Unfortunately by the time an aftermarket coolant is put in the system, the vehicle has often already been abused and the coolant system neglected.

In addition, distilled water is recommended, but often not used for mixing. Hard water or city-treated water can also reduce the life expectancy of coolant, and can also cause sludge or lime build-up. Be sure to use distilled water for the most life out of the coolant system.

This being said, mixing can be an issue if you use the wrong coolant, and by wrong I mean a totally different chemical. Mixing Propylene Glycol such as Sierra and Prestone Low-Tox with any Ethylene Glycol based coolant will cause gelling. Low-tox and Sierra are rare in most areas, but may become more popular due to its supposed lower impact on the environment. DO NOT MIX EG and PG based coolants!

Prestone Low-Tox: Prestone Low Tox Antifreeze Specifications

Sierra Coolant: SIERRA Antifreeze Product Page (FAQ)

More reading: Audi Coolant - Audi G11 G12 Coolant - Pink Purple Audi Coolant