Calling all G12 experts

.. To start off with i got a 1993 Vr6 SLC with 110000 mi on the clock. the coolant was brwon so i decided it was time for a complete flush but only converting it to the new g12 (pink) coolant. I had a reptable raditor shop do it and and every thing was fine. Now 2-3 weeks later the coolant is already brown and dont know what it could be...

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If the coolant is brown, it'll turn into sludge soon. ..

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Volkswagen uses two different types of coolants that are identified by color. The older blue version is know as G11, and the newer red version is G12. Both of these coolants have different characteristics and should not be mixed! Depening on model year and what's printed on your coolant resivior is what coolant type you have in your MK3. Due to the limited availability of G11 coolant, G12 is compatable to install but the existing G11 coolant must be removed and flushed first before adding; if mixing occurs, a chemical reaction between the two coolants with result in a brown thick sludge build-up in your cooling system.

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... It's an OAT (organic acid technology inhibitor) coolant, and it doesn't mix well with anything else. In fact, it'll gum up and turn brown, and various things will start corroding fast.. Even the VW blue coolant will do the same thing mixed with it.

So, DO NOT MIX G12 with anything!

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...GET IT OUT OF THERE NOW!!!!!!! TAKE IT SOMEWHERE AND HAVE THEM COMPLETELY FLUSH IT!!! If G12 (OAT inhibitor) coolant is mixed with conventional coolant that uses silicates as an inhibitor are mixed, they turn acidic and start eating your engine *QUICKLY*. They also turn into a gummy substance and you get chunks flowing around and plugging things up. Flush it COMPLETELY, blow it out with air and flush it again.


The VW TSB that talks about retrofitting cars that came with blue G11 (very similar to green Prestone minus the phosphate inhibitor) says to do a thorough flush and blow out with air, you don't want them mixing.

If *any* fluid is a different color, you need to be on alert that it probably isn't compatible. Even same color fluids aren't compatible a lot of the time (take dex-cool and damiler-chrysler hybrid-OAT coolants, they're both orange but they're not the same)...

Yes, G-12 is proprietary, but many, if not most, other cars are coming with a proprietary coolant. Ford is the only one that's using the old green stuff in almost everything. I think the new Cougar is the only thing that they used OAT in for a while... Japanese coolant is low silicate, high borate. Very few things mix...

.. if your Passat is 10 years old, it must have originally come with G11 blue coolant. I'm assuming someone did the proper flush and change!?!? VW started factory filling with G12 in mid 1997 model year, right around the same time as they change to the single row upper timing chain....

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I would flush out the system. Mixing coolant now-a-days is predominat user error problem. It's like the same problem with the green freeze / GM Dex-Cool phenomenon: once mixed, it chemically reacts and forms a thick brown rusty sludge. Like SequoiaGLX said, It's disgusting, and hard to remove from the system with a chemical / pressure flush.

Customers assume orange = green and add in whatever is laying around the house. If you don't know, you can always add distilled water to the system. But there's nothing in the manual about specifics? That's odd... even my 1997 owner's manual + coolant tank specifically ask for G12. I think in your best interest and life of the hoses, water pump, and etc., get it flushed out and filled with the correct coolant specifications.

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When I got the car the coolant was brown sludge so I changed it pretty fast. Then it started to leak coolant everywhere (thermo housing etc). Looks like I was too late and changing it made it worse for some reason. The pitted area was all rusty and bits just flaked off !! Let this be a lesson to you all to maintain your cars. lol I suppose a lot of high mileage engines go like this (before they die)


There's no room to deck the block, the pistons go to the top of the bores don't they. although it looks bad i'm hoping there will be a good seal around the cylinders as its not corroded at all around them.

ps yes the cardbord is to stop bits of rust getting in the engine - I'm surprised I still care about the car to have bothered.

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I have a 2002 Eurovan that was topped off with non G12 coolant. It was about 6 ounces of PEAK phosphate free, glycol-based coolant. The mechanic thought the red stuff was the same as the red stuff in the reservoir

Question: do I need to flush my system and replace with new G12?

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And, yes, mgwerks, I am going to do exactly what you said.

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VW Hat doch nur noch G12+, das mit G12 UND G11 mischbar ist!

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houston, may I make a minor alteration to Mark's suggestion, which I agree with? If you're going to have it all cleaned up and flushed, you should convert to the newest VAG coolant: <font color="purple"> G12+ which is purple in color. </font> It is more forgiving when mixed with other products and IS compatible with both G11 and G12 !! That would be the way to fly, IMO.

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So if a VW has purple coolant, how does one know that it has only G12+, or whether some G12 or G11 is mixed with the G12+?

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