Silica bag in coolant reservoir

[Boatman1]

I have a 2014 Octy estate which had a bag of silicon in the coolant reservoir. I have suffered 2 blockages of the heater matrix after which the bag was removed, the coolant had turned a gungy rust colour. After running the car for a year without the bag, the coolant is once again discoloured. I contacted Skoda to ask why this silica bag was installed in the reservoir, the unsatisfactory answer was that the reservoir was made by a third party company who are not part of the VW group and the reservoir came with the bag already inside it, they could offer no technical reason as to why it was there. Has anyone come across similar problems?

[MATT0693]

The silica bag is a well documented issue across the VAG group.
A VW tech told me it was to prolong the coolant life over time, so it should last the lifecycle of the car.

It seems a little pointless to me as most cars are going to have coolant pumps changed every 5 years anyway, it makes sense to flush the system and renew.
My tank was double walled to the bag can't be removed, so I swapped it for a non-silica version and change the coolant at the same time.

 

[Gaz]

There are multiple threads on the Coolant tank and silica bag.  E.g.:

 

Gaz

[NikTheGeek]

The silica bag adds protection to the internal metal surfaces of the cooling system, something the coolant loses the ability to do with age. Removing the bag, just means you need to replace the coolant at a sensible interval, rather than it being in there for the life of the car.

[TheClient]

3 hours ago, Boatman1 said:

I have a 2014 Octy estate which had a bag of silicon in the coolant reservoir. I have suffered 2 blockages of the heater matrix after which the bag was removed, the coolant had turned a gungy rust colour. After running the car for a year without the bag, the coolant is once again discoloured. I contacted Skoda to ask why this silica bag was installed in the reservoir, the unsatisfactory answer was that the reservoir was made by a third party company who are not part of the VW group and the reservoir came with the bag already inside it, they could offer no technical reason as to why it was there. Has anyone come across similar problems?

Gee whiz you got the 5 o'clock Friday crew responding to you!!  What a load of [insert chosen expression.................]  Are they so devoid of understanding how part suppliers work with Automotive manufacturing that they could spin you that!  The supplier that manufacturers the coolant bottle manufactured it to VWAG specification including the Silica bag!!!

 

The wording in the VW self training guide is from memory more to do with high heat loads and the amount of silicate available in G13 being depleted, not directly referencing time.  But make no mistake it was a very deliberate design feature designed and added to the reservoir tanks for a reason.

 

Was your bag actually split and leaking granules, if not something else may be at play? If it was leaking, it is very difficult to clear the coolant system especially the heater matrix.

 

Edited 18 October, 2021 by TheClient

[Boatman1]

Agree with you (the client) they treat you like a fool, my silica bag was intact the matrix was completely blocked, the garage couldn't unblock it, needed a new one.

[varaderoguy]

I think that the whole issue with the Silica gel bags is not a good look for VAG and they have clammed up and not even put out a TPI on it (because fixing the whole shebang would cost billions)...I digress....

 

Removal of the Silica bag is recommended as PM (or changing the header tank)....I also recommend going back to a 5 yearly coolant change.....and if the coolant is a yukky colour then get it changed asap and refilled with fresh G12evo.

Edited 19 October, 2021 by varaderoguy

[Vahids]

I am also thinking about flushing my car's coolant (not having a Silica bag, but it is pretty old)! Do we have any guide which shows how to flush the whole coolant (radiator + engine)? My main issue is how to flush the bit inside the engine as thermostat is closed when engine is cold! 

[NikTheGeek]

11 minutes ago, varaderoguy said:

I think that the whole issue with the Silica gel bags is not a good look for VAG and they have clammed up and not even put out a TPI on it (because fixing the whole shebang would cost billions)...I digress....

 

Removal of the Silica bag is recommended as PM (or changing the header tank)....I also recommend going back to a 5 yearly coolant change.....and if the coolant is a yukky colour then get it changed asap and refilled with fresh G12evo.

 

And if you have your car serviced, simply get them to change the coolant when the timing belt and waterpump is done as you lose some anyway! That would match the required coolant change intervals perfectly.

[TheClient]

19 hours ago, Boatman1 said:

Agree with you (the client) they treat you like a fool, my silica bag was intact the matrix was completely blocked, the garage couldn't unblock it, needed a new one.

If the silica bag was intact then it can't be that then if the granules were still encapsulated within? It is the granules that get circulated and block.  What do you think blocked the matrix as it seems you have the same problem agian?

[NikTheGeek]

20 hours ago, Boatman1 said:

Agree with you (the client) they treat you like a fool, my silica bag was intact the matrix was completely blocked, the garage couldn't unblock it, needed a new one.

 

Isn't the other cause of a blocked matrix sand left over from the casting process? That might explain the colour of the coolant too....

[TheClient]

16 hours ago, NikTheGeek said:

 

Isn't the other cause of a blocked matrix sand left over from the casting process? That might explain the colour of the coolant too....

Quite possibly, although I haven't got any direct experience of that being a problem. Presumably they still cast the blocks with sand.   But if that was to apply in this case and with the silicate bag being intact, the whole issue of blocked heater matrices for @Boatman1 are not related to the silicate bag in the reservoir. Or, there is a different cause and/or the Matrix is not actually blocked this time? What was found in the blocked matrix last time @Boatman1?

 

Lots of posts on the forum regarding blocked mk3 matrices, this is just one of such posts below, and mostly relates to vRS, but there will be some commonality in cooling system arrangements there may be a faulty valve in the system.

 

 

[Boatman1]

On 19/10/2021 at 15:51, TheClient said:

If the silica bag was intact then it can't be that then if the granules were still encapsulated within? It is the granules that get circulated and block.  What do you think blocked the matrix as it seems you have the same problem agian?

A gungy rusty coloured deposit was being produced in the cooling system, I assumed the coolant was being broken down due to heat. Silica is usually used for air absorption, not clear on why this would be added to the reservoir and could get no sense out of Skoda.

[NikTheGeek]

15 hours ago, Boatman1 said:

A gungy rusty coloured deposit was being produced in the cooling system, I assumed the coolant was being broken down due to heat. Silica is usually used for air absorption, not clear on why this would be added to the reservoir and could get no sense out of Skoda.

 

It coats the aluminium internal surfaces, providing enhanced corrosion protection by replacing the silica that is lost by the coolant as it ages. There's no need for the silica bag if you regularly change your coolant (every 5 years for example) rather than leaving it in for life.

 

HTH

[TheClient]

14 hours ago, NikTheGeek said:

 

It coats the aluminium internal surfaces, providing enhanced corrosion protection by replacing the silica that is lost by the coolant as it ages. There's no need for the silica bag if you regularly change your coolant (every 5 years for example) rather than leaving it in for life.

 

HTH

That aligns with what I've read. In the vw self study it says something like...... high heat load applications deplete silicate content over time and affect corrosion protection, so the silicate repository keeps adequate levels by replacing lost or degraded silicates in solution....

 

Interestingly if you google silicates in coolant there is ....almost.... as much discussion as engine oil choice - almost. Some manufacturers preferring not to use silicates as if the solution becomes too weak (possibly from degradation) it is actually detrimental to corrosion protection than having no silicates at all.... There's even a research paper I came across and different vehicle manufacturers have a different attitude towards using silicates in coolant VAG vs say Honda for example.. 

 

All over my pay grade but if you've got a mind for science plenty of reading!!!...

 

 

[Boatman1]

On 02/11/2021 at 18:46, NikTheGeek said:

 

It coats the aluminium internal surfaces, providing enhanced corrosion protection by replacing the silica that is lost by the coolant as it ages. There's no need for the silica bag if you regularly change your coolant (every 5 years for example) rather than leaving it in for life.

 

HTH

update, had the cooling system flushed, new coolant same colour as the old stuff after 100 miles, also loss of coolant about one pint, could be down to an airlock but am regularly having to top up the coolant, no overheating of engine according to the gauge but am beginning to think head gasket car has only done 59K any ideas welcome.

[MATT0693]

1 minute ago, Boatman1 said:

update, had the cooling system flushed, new coolant same colour as the old stuff after 100 miles, also loss of coolant about one pint, could be down to an airlock but am regularly having to top up the coolant, no overheating of engine according to the gauge but am beginning to think head gasket car has only done 59K any ideas welcome.

 

Has the coolant system been pressure or dye tested? 
If you are loosing coolant and there are no external leaks, then it is either being burned or the pressure cap has failed.

I would get the system tested for combustion gases to rule out head gasket/cracked head etc, you can buy the kit for under £50 or get a garage to do it.
 

[NikTheGeek]

You can get a home test kit to see if combustion gases are entering the coolant. A replacement cap is a cheap test. Have you checked the water pump isn't leaking? A little leak might burn off. You can put a flourescent dye in to check for dried leaks.

[FrankLK]

I removed the bag but I don't want to replace the coolant for now, due to sensitive plastic water pump housing. Coolant has normal colour, until I have some problems, I will leave it like it is. 

[Warrior193]

4 hours ago, FrankLK said:

I removed the bag but I don't want to replace the coolant for now, due to sensitive plastic water pump housing. Coolant has normal colour, until I have some problems, I will leave it like it is. 

Hi Frank, just be aware that the silica 'tea bag' is there to extend the service life of the coolant. A good idea to at least stick to recommended coolant change intervals with bag removed. 

[FrankLK]

Yes, true, I think if it was in system for 3 years, silica is in system, couple of years without a bag will be no problem.Then maybe I will sell it anyway😁

I heard that water pump on my engine is prone to leaks and failures, (plastic crap) so the coolant change I will postpone for now or until pump leaks. 

[roaddetective]

Just changed my silica bag filled Expansion Bottle for the one without the bag today. Love an easy job as it took no more than 10mins to complete. Car is on 32k miles, so I think I will have the coolant changed at the 40k mile service and every other service afterwards. Change the coolant frequently, just like the old days.   

[Stokesy]

15 hours ago, roaddetective said:

Just changed my silica bag filled Expansion Bottle for the one without the bag today. Love an easy job as it took no more than 10mins to complete. Car is on 32k miles, so I think I will have the coolant changed at the 40k mile service and every other service afterwards. Change the coolant frequently, just like the old days.   

Would you mind posting a link to where you got the bottle without the silica bag from please? Cheers

[roaddetective]

15 hours ago, Stokesy said:

Would you mind posting a link to where you got the bottle without the silica bag from please? Cheers

Although I ordered mine through www.hortonskoda.co.uk and got it posted to me, with the correct part number you should be able to get it through any VW/Skoda garage. Part number is- 5Q0121407M. 

[Stokesy]

Perfect, thankyou