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I have just bought my first TDI (2004 Jetta w/120000 miles) and due to lack of maintenance records I'm going through the whole car and replacing all fluids. The engine coolant looks brown and nasty so I' assume its been mixed with some uncompatible brand or maybe never changed before and at the end of its lifespan. I'm getting ready to do timing belt in the next week or so and was wondering if G12 coolant is all these cars can use or if a complete flush is done the system can be converted to coolant easily found at local parts stores? If so which coolant is prefered?

If not easily converted from G12 then how much will be needed to replace?I've noticed from online vendors that no more than (2) 1.5 liter bottles can be shipped due to HAZ MAT regulations. Thanks.
 

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If you do a complete flush, you could use green Prestone. HOWEVER, I would not for a number of reasons. G12 is long life and will outlast prestone, I forget the exact chemistry, but G12 will not eat the aluminum, and G12 will not cause buildup on the water coolant passages. It really is a better coolant. G12 does not look brown and nasty after high miles so I'm pretty sure it's been mixed.

http://www.myturbodiesel.com/1000q_how_to/a4/coolant_flush.htm Here are some tips - note the section on thoroughly flushing the system. I would also replace the reservoir tank. It's cheap and if you had mixed coolant it's probably crusted and stained inside. I've had lots of G12 shipped to me before with no restriction. mjmautohaus has a deal on G12 if you buy a lot.
 

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Ewwww... stick with the G12. It's made specifically for VWs and works best. There are plenty of pics of sludged up coolant out there. Make sure you don't have any leaks either - you dont know why the PO put coolant in there.
 

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I recently bought an '02 Passat TDi and was also intending to do all the fluids, for peace of mind. The coolant in mine looked OK, ie not obviously brown, but I discussed it with a reputable VW / German vehicle garage. Their opinion was that since it had G12 in from new he would not recommend changing it until the timing belt / water pump was due (about another 12 months for my car).

Obviously, because your coolant does look contaminated it would be wise to get it flushed, but the conclusion I came to was that even though the G12 is quite a bit more expensive it does have a seemingly proven ability to protect the engine for a loooong time, as opposed to the regular green stuff that should be changed every 2-4 years.

In the long run I feel that G12 would work out cheaper, especially if you intend keeping the car for at least four years or more.

Just my unqualified 2 cents worth ;)
 
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