Applicable to Passats and all other VAG vehicles.
I am not entirely sure of which Passats might be affected by this, but it actually affects ALL VAG vehicles of a certain age, (probably about 2013 model year onwards), hence this seems the best place to post.
When I first saw a Youtube video of someone removing a small bag of crystals from the coolant reservoir of a VW, and binning it as a precaution, I assumed it was a joke of some kind, but being curious I investigated further.
Now, if you think this is a wind-up I will not blame you for a moment...... but it is not.... it is actually a ticking time bomb in certain cars that can end up costing the owner a considerable amount of money.
I have not looked greatly into it because my car is old enough to not be affected, so this is a summary of what I have found, but you may find much more detail on-line.
It appears to affect some cars built with a coolant reservoir marked for G13 coolant, AND with a square printed on the reservoir with the words 'Mit Silikat'.
An ingredient of the coolant additive is a silicate material which is there to protect aluminium components from corrosion. This silicate, in time breaks down and loses its efficacy. With G12, (and the much earlier G11), it is not a major problem because it was recommended to change the coolant at certain intervals, (even if only when the water pump is changed and a lot of the coolant is lost in the process).
However, it seems that G13 was to be hailed as a 'fitted for life' additive, (presumably to be re-used when the pump is changed).
To overcome the degradation of the silicate, a bag, (which has become known as 'the tea bag'), was placed in the inner chamber of the reservoir, (the part visible when the cap is removed). This bag is made of a permeable plastic and contains a quantity of silicate, (basically sand), which is supposed to gradually replenish the silicate level in the coolant over the years.
As anyone with the slightest degree of cynicism, (or life experience), will by now have guessed, these bags can split with age, and then dump their contents into the coolant.
This make the coolant dirty, (from the bright pink/mauve to a dirty orange/brown), which is bad enough of itself. Worse is the fact that the silicate travels around the cooling system, but the killer is the fact that is gets trapped in the heater matrix, blocking it and requiring the matrix to be replace, (back flushing apparently does not work).
- Incidentally, if this has happened to your car, do not try to fix it yourself, or have an independent garage fix it, because it is apparently impossible to remove the silicate from the system, and it will very soon block the new heater matrix, meaning the job has to be done again. Dealer workshops have access to a special tool specifically for flushing the entire system of this silicate.
Later versions of the reservoir have the bag in the outer section of the reservoir. This is an improvement but it seems the problem can still occur.
It is now possible to obtain a reservoir that does not have the silicate at all, which is fine so long as you ensure that the coolant is replaced every so often, (perhaps when the pump is changed).
This is a potentially very expensive problem for owners, one that can be prevented if you act in time and get rid of this silicate.
A long and detailed thread, written by people better informed than me and from which the photos were extracted, can be found here:
https://www.briskoda.net/forums/topic/4 ... placement/
Potential catastrophic failure, & how to avoid it
Moderators: water01, vwnutant, desertstorm
Potential catastrophic failure, & how to avoid it
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