Silica Bag - Coolant MQB Engines

Boydie

Boydie

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This may have been brought up before but after a quick search I couldn't find anything.

I recently heard about these bags which are located inside the MQB engines (may be others) within the coolant tanks. They are small bags of silica which are designed to preserve the life of coolant but over time it has been known for these to burst and cause mega problems within the coolant system. Not a good thing for cars out side of warranty!

Anyway, here is a short video (not me) of how to remove it, I will be doing this today hopefully if the weather isn't too bad!

 
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I have never heard of this before!!! Very interesting...I’ll have to have a look to see if mine is there (15 plate S3)
 
This is probably one of those things like the suspension block that’s gets forgotten about during the PDI. I just cant see what a little bag of silicon is gonna do In What is essentially water circulating round and round
 
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The silicate bag is there for a reason, and VAG isn't the only manufacturer who does it apparently. Mercedes does it as well.

From one of VW's Self Study Program 514 page 31:

Coolant Expansion Tank with Silicate Repository

The coolant expansion tank contains a silicate repository. Silicate is used to protect the aluminum components in the coolant
system from corrosion. There are silicates in the G13 coolant, but they are used up over time if the engine is subject to high
thermal loads.

To compensate for the silicate consumption, silicate is taken from the repository and added to the coolant. The silicate
repository provides additional protection against corrosion for the aluminum components in the coolant system over the entire
lifespan of the engine.
 
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I'd rather risk it bursting than risk aluminium parts of the cooling system rusting because silica from coolant has been used up without me knowing it.
 
My inclination, for what it's worth, is to assume that the blokes who design the engines know rather more about all this than I do.

I'm not going to start removing components just because there's a possibility they might go wrong.

.
 
Phutters said:
My inclination, for what it's worth, is to assume that the blokes who design the engines know rather more about all this than I do.

I'm not going to start removing components just because there's a possibility they might go wrong.

.
Click to expand...

Agree to this to a point but the blokes who design these thing also just need it to last the warranty period. Temporarily stopping corrosion in the coolant system is just that , temporary. That bag of silicon isn’t gonna last forever. In my head if it isn’t designed to last then should be changed like a service item especially if there’s reports of it bursting and running a muck
 
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Have you one inside the coolent tank of your car, has anyone here in this forum actually reported having one? Your assumption that parts in a car, aside from renewable ones, are only designed to last the length of a warranty is a tad cynical...
 
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Just got mine out took 5 mins, car wasn’t worth having warranty after a few month from new anyway so....
 
Yes, I have one in my 2014 A3. Visible when using a bright torch shining through the purple G13 coolant.

Per the Self Study Program, VAG designed the silicate bag to continue supplementing the coolant for the lifespan of the engine. Regularly extracting old coolant and topping up with fresh coolant may be beneficial, but how many people actually do that? Most people don't even check their oil level regularly, let alone top up their coolant tanks.
 
Can you just replace it with a new one? Mine is now 4 years old and I do not plan to keep the car another 4 years so just replace it with a fresh one?
 
I doubt it is available as a replacement from Audi, if it is designed to last the life of the engine. Your best option is to renew the entire coolant expansion tank if you want a new bag.

There has been no evidence of widespread failure of the silicate bag on the MQB platform. In fact, it is found in both VWs and Audis for the past 10+ years, and if this is the first time many are even hearing of a silicate bag in the expansion tank, then it is clear that failure rates are extremely low.
 
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Sean6211 said:
I doubt it is available as a replacement from Audi, if it is designed to last the life of the engine. Your best option is to renew the entire coolant expansion tank if you want a new bag.

There has been no evidence of widespread failure of the silicate bag on the MQB platform. In fact, it is found in both VWs and Audis for the past 10+ years, and if this is the first time many are even hearing of a silicate bag in the expansion tank, then it is clear that failure rates are extremely low.
Click to expand...
...........as above first time i've heard of this?.
 
Googling around, it seems that several VAG cars, and some others, have silicate reservoir cartridges in the radiator header tanks. Not seen any mention of problems, and they have been in use for more than 10 years, so leakage can’t be a major issue. Should anyone want replacements, there are several listings on eBay.
 
Hey guys.
I too had never heard this, but I have just had my Passat in for a service and they told me that the bag had burst and would contaminate the coolant system and eventually block the coolant heater matrix.
The coolant expansion tank needs replacement at a cost of £650.
The car is 6 weeks out of warranty :frown new:
 
Get them took out ! Never used to have them.
 
Modern coolants like G13 contain only the minimum amount of silicate needed to protect the water pump from corrosion. Older formulations used loads of silicate, so would never deplete - but had the opposite problem, the high levels of silicate could congeal into a sludge after a few years.

Silicates degrade with time. The problem with low silicate coolants, is that because they only have the minimum dose from the factory, they have a limited lifetime before they stop working. To get around this some manufacturers put silica beads in the coolant which gradually leach silicate into the coolant to counteract the depletion.

Removing the silica beads will shorten the life of the coolant, and you should think about draining and replacing the coolant every couple of years if you want the water pump to last.
 
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I have changed my coolant and will change it again.
 
ZipZap01 said:
Modern coolants like G13 contain only the minimum amount of silicate needed to protect the water pump from corrosion. Older formulations used loads of silicate, so would never deplete - but had the opposite problem, the high levels of silicate could congeal into a sludge after a few years.

Silicates degrade with time. The problem with low silicate coolants, is that because they only have the minimum dose from the factory, they have a limited lifetime before they stop working. To get around this some manufacturers put silica beads in the coolant which gradually leach silicate into the coolant to counteract the depletion.

Removing the silica beads will shorten the life of the coolant, and you should think about draining and replacing the coolant every couple of years if you want the water pump to last.
Click to expand...

Very informative post :icon thumright:
Didn’t know any of that till now.
 
I had this on my A3 1.8TFSI Quattro at 3-years/35K miles. Fortunately it was still under factory extended warranty, I wouldn’t have wanted the bill.

Dunno, feels like an unnecessary cludge to me, why not just design a more appropriate coolant than have something floating around which can burst and clog everything up?

Quite apart from the main rad, I would not want to have the DSG (S-Tronic) coolant valve blocked and have a £10,000 gearbox overheat and go South because some numpty designer stuffed a silicone teabag in the expansion tank instead of speccing a service life for the coolant.
 
Just had this happen on my '16 2.0tdi Octavia Scout - Coolant level suddenly dropped and the reservoir looked v murky. Driver's side fans 8degrees cooler than the left.

Car 7 months out of 3-year warranty.

Garage presented a quote for a 'discounted' £1030 (discount due to TPI) for flush and new heater matrix. I complained heavily and was referred to Skoda CS. Within 2 days I had a 55% contribution from Skoda!

Took the sting out a little but still an avoidable headache - the garage told me they don't inspect the silica bag at all when checking coolant during service!!!

- They also informed me it was the second case they'd had that week and they'd had 9 others in as many weeks. :blink:
 
Last edited:
Beags said:
Just had this happen on my 2.0tdi Octavia - Coolant level suddenly dropped and the reservoir looked v murky. Driver's side fans 8degrees cooler than the left.

Car 7 months out of 3-year warranty.

Garage presented a quote for a 'discounted' £1030 (discount due to TPI) for flush and new heater matrix. I complained heavily and was referred to Skoda CS. Within 2 days I had a 55% contribution from Skoda!

Took the sting out a little but still an avoidable headache - the garage told me they don't inspect the silica bag at all when checking coolant during service!!!

- They also informed me it was the second case they'd had that week and they'd had 9 others in as many weeks. :blink:
Click to expand...

In the US they would have had a class action lawsuit by now if there were that kind of failure rate, and VAG would be footing the bills or recalling the vehicles. Here, though...

Anyone know if we owners can simply replace the silicone bag every year just as a service precaution? How much could a silicone bag possibly cost?
 
Take the bag out and replace the coolant.
 
I was told that Audi's don't have them but VW Golf's do and they are a pain as they get stuck in the heater rad
 
MikeParkin said:
Take the bag out and replace the coolant.
Click to expand...

What's the procedure on these cars? I wouldn't hesitate to do this on my older Audis and Golfs, but I know Audi now use a pressurised cooling system filler which automatically purges air from the system. On some cars there was a VCDS procedure for activating the Aux heater also, so it's possibly not a trivial thing?

I'll call my friendly local parts dept shortly and see if the bag can be had as a service part.

Sparks43 said:
I was told that Audi's don't have them but VW Golf's do and they are a pain as they get stuck in the heater rad
Click to expand...

It's true they clog the heater rads when they go, seem to be more reports on the VW forums, but they're possibly just more active forums? It's not true that Audis don't have them, though, several confirmations on this thread alone and I've had one go and been replaced/flushed by Audi under extended warranty.
 
Right just spoken to parts. Doesn't seem like the bag is available separately, comes with the expansion tank. £27 inc VAT genuine from Audi. Considering how much easier/cheaper this is than a complete coolant flush, I'll be doing this as a 2-yearly service item. At 1/3 price of the oil at an oil change interval, I'd say it's a no-brainer.

If the worst does happen, you're looking at £79 just for the specialist flush kit Audi have to use when these go south. Plus possibly the cost of a heater matrix and a lot of labour, although looking back at the job on mine, it seems they got away with a proper flush and didn't have to do the heater matrix, so maybe that £79 was worth it after all...
 
I changed my radiator when I put my Wagner intercooler on. I did exactly as you normally carry out a drain and change.

It has been spot on since then and that was over 2 and a half years ago.
 
Good to know it's just a normal drain/fill procedure.

Yeah, it's certainly an option to just change the coolant out every so often - do we know the age/mileage interval that the coolant is supposed to have depleted its silicate supply without a bag in the system, or is it dependent on driving conditions/style, etc.?
 
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