Coolant blown out from expansion bottle

shocks said:

Yeah i agree there's nothing definitive in my experience so far, just thought I'd share my experience, especially the combustion air testing bit as I thought it's mad that both my golfs tested positive. I'm going to hold of on the heater matrix and see if it was the head gasket. That should be interesting, I clearly have a lot of combustion air getting into my system to get a yellow test result. Others are having this problem too, even after changing the matrix, and may want to know if a head gasket replacement has helped. As I said Ill keep you posted but I suspect due to the frequency that the regen cycle and heater matrix were the root cause.
On the pump, I've gone like for like, based on the electronic parts catalog I asked VW parts for PN 04L121011P but they gave me PN 04L121011L. It has a solenoid and shroud so I assume its variable. The existing is PN 04L121011 first gen I believe but I'll confirm that soon. Why do you ask, is there some known issue with the variable type?

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Sorry, I meant to say that I didn't have any new insights for you, not that your experience wasn't worth sharing; it absolutely was!

As for the pump, there have been a small number of reports of pump shrouds sticking in the "cold" position, causing overheating. In the U.S., apparently the dealers are now supplying non-variable pumps as standard replacements, so I was curious what was happening in your part of the world.

RIP TDI said:

As for the pump, there have been a small number of reports of pump shrouds sticking in the "cold" position, causing overheating. In the U.S., apparently the dealers are now supplying non-variable pumps as standard replacements, so I was curious what was happening in your part of the world.

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That's interesting but no, they didn't mention anything like this. Mind you I stopped asking to parts dept for parts by name because they given me the wrong parts on a number of previous occasions. Because of all the work I'm doing at the moment (I'm also changing the timing Belt on the MK6), I paid for a 1 month subscription to https://www.partslink24.com/ so I can access the electronic parts catalogue. It's a really good resource because it gives you only the parts and exploded diagrams specific to the cars VIN and also the RRP of the part which isn't available on a VW website here in Australia like it is in the US and Europe. The VW workshop service manuals, which I think are pretty decent and very detailed, I downloaded from ERWIN.
Interestingly the current heater matrix part on the Electronic Parts Catalog is still 5Q0819031A and haven't been superseded, it doesn't seem like VW are acknowledging an issue with the part here at least!
The reason I mention all of this is because, as others have pointed out, some of these repairs are approaching uneconomical on these vehicles, mm-rocco what quoted $2,300 eur - 4,400 eur for the head gasket repair and head replacements respectively. This was similar to the prices I got too and it's not really a ripoff, it's a tonne on work on these engines to do this job. For me the cost could be up to 50% of what a working version of my car is worth.
As I said, if anyone else hasn't solved the issue with the Matrix alone, I'm happy to share any manuals, photos, or advise (such as alternatives to special VAG tools) based on my experience, if you want to take the job on yourselves.

RIP TDI said:

there have been a small number of reports of pump shrouds sticking in the "cold" position, causing overheating.

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I think this could very well have been part of the problem, I've removed the old pump and sure enough when I pull the shroud over the impeller it's sticking and won't snap back by itself. Who know though, maybe it worked fine under normal engine temperatures and the hydraulic pressure of the coolant. It doesn't seem right though but, unfortunately, I didn't check this until after I'd completed the timing belt installation so I can't compare the action on the new pump.

Just out of curiosity, when you checked the coolant and the result was yellow, did your tester touch the coolant?
Also, what were the exact symptoms? Coolant got out at regen or at prolonged high load?

The test wasn't contaminated with coolant, it's hard to get coolant in the test fluid when there's no coolant left in tank also, my tester is a double chamber design so coolant cant get into the top chamber unless it fills the bottom chamber first. Each time I lost coolant was during a longer drive, 160kms or so driving 110km/h, aircon on, 25 to 35 deg C outside temp. I could have had a regen cycle but I never noticed one as it wasn't on my radar at the time.

Thanks for the reply. I’m experiencing the same problem as you and have ordered a coolant tester and I’ll do the same testing as you. Until then, I’ll wait to see if you can resolve it with the headgasket. I doubt that the headgasket is at fault one way or another, I think it has something to do with deposits building inside the whole cooling circuit and blocking some of the parts, which may lead tot their failure.

Yeah, I'm hoping it's the gasket but I'm not convinced either, hence the reason I found this forum half way through the repair. The fact is though, whatever the root cause (dodgy water pump shroud, heater matrix or otherwise), exhaust gas is entering the coolant system which shouldn't be happening and I want to address.

Correct me if I'm wrong but other than the engine block, the only other places I could see where exhaust gas could enter the system giving the positive gas test readings are the EGR Cooler (is there enough exhaust pressure?) and the charge air cooler.

There's a diagnostic tester based procedure for testing for EGR leaks in section 5.7 of the workshop manual I came across during during the repair. I'm not sure how this works but I'm going to try that once I've gotten it running again. There's also a procedure in section 2.5 for the charge air system but it doesn't seem like a very robust test (you maintain a constant 0.5bar of air pressure in the unsealed charge air circuit and use a manometer to ensure pressure in coolant tank doesn't rise by >0.051bar). I'm going to pressure test the charge air cooler directly via its coolant inlet and outlet points this weekend before refilling the coolant circuit. I also planning to do the same with the EGR cooler. The pressure test I previously performed at 1.5bar on the entire coolant system didn't show any leaks but it's worth doing before I replenish the coolant.

I think the easiest way to detect if the heater matrix is the problem or not if you test the heating in the cockpit. I know there is end of summer your location, means not easy to test the heating, but for myself beside the coolant loss during DPF regenerations was the poor heating or the fluctuation of the set temperature during long journeys. If you have a look for the water circuit of the EA288 engine (http://pics3.tdiclub.com/data/517/820433_EA288.pdf page 22) you can see that through the Heater matrix (symbol 3) there is a constant water flow from the EGR cooler (symbol 4) independently if you want to heat or cool inside the cockpit. During normal using if your Heater matrix is partly clotted it could be enough to keep below the overheat temperature the water temperature, but during EGR regeneration the EGR heater has much higher temperature as well. If the Heater matrix is unable to let flow trough the overheated coolant in can blow out. The built in water temperature sensor inside the cockpit is blind about this temperature, because it measures the temp. of the engine block instead of this temperature).Luckily there is an overflow pipe between the EGR cooler and the Heater matrix towards directly to the Expansion tank, so if your heater matrix is partly clotted this problem can occur so easily. I don't think that after 110k miles a VW engine head gasket could be damaged (except if the driver used it as a gokart), and if you search back maybe this thread or in other forums, there was a guy, who totally changed the entire engine of the Car with the all of the Water elements, except the Heater matrix, and after few hundred miles totally the same problem occurred. So, I would recommend to start with the heater matrix and see how the things will going after it.

kisvamos said:

I don't think that after 110k miles a VW engine head gasket could be damaged (except if the driver used it as a gokart)

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Is there any other way to drive this car But yeah seriously, who knows, the water pump I just removed doesn't fill me with confidence that I was even circulating coolant when it was needed, have a look at this .. https://imgur.com/LQNKp92. If the shroud wasn't retracting reliably, this could certainly in theory cause overheating in the block and resulted in a leak at the cylinder head.

The fact of the matter is though, over a period of a month, I tested the coolant at least 10 times and every single test showed exhaust gas was present in the coolant system, the last test performed immediately after coolant was ejected went yellow indicating a very strong presence of exhaust gas.

I've just bought a new Passat, it's got the same EA288 engine and an almost identical setup, I've tested this car, hot and cold, and the test fluid does not change colour.

I'm definitely not discounting the loss of coolant possibly being caused by the heater matrix issue, however this doesn't explain the exhaust gas in the system. Indeed, if you look though the forum a number of people have not solved this problem through replacement of the Matrix alone, mm-rocco for example tried a few different things, and in his last post he was still facing a 2400-4400 Eur head gasket repair. Believe it or not, parts wise, the head gasket change I just did, was one of the cheaper options I could have chosen to perform, it just took a lot of time but I like working on cars and I've learnt alot from the experience.

My plan of action this weekend is, pressure test the EGR Cooler and Intercooler as I mentioned in my last post. If all is good, I'll refill the coolant and then once I'm happy it's running okay, I'll probably take it on my daily commute (50km each way). I'll then test for gas when cold the following morning (as this always resulted in a positive exhaust gas test in the past), if all is good then I may force a regen following my next long drive and see if I can get a pressure rise in the coolant system and rule the heater matrix issue in or out.

Hi Folks, i noticed this topic is coming back alive with some new members with simular problems.

After the replacement of several hoses, the heater matrix and the EGR Cooler i still have coolant problems. The good news is that (with the help of a sillictor) the car goes back in repair soon (again). In the meantime i found a way to deal with the coolant blow-out issue ! When i arrive to work (30-100km depends on the worklocation of that day) i release the pressure of the coolant-system by releasing the cap of the coolant-reservoir. If i fail to do so the car will welcome me the next time i start him up with a message "Coolant Low, please refill" and a sound. If i release the pressure just after the drive i will be fine. The other thing is that i do not drive over 100 km/h which is very slow for a GTD.

shocks said:

Yeah, I'm hoping it's the gasket but I'm not convinced either, hence the reason I found this forum half way through the repair. The fact is though, whatever the root cause (dodgy water pump shroud, heater matrix or otherwise), exhaust gas is entering the coolant system which shouldn't be happening and I want to address.

Correct me if I'm wrong but other than the engine block, the only other places I could see where exhaust gas could enter the system giving the positive gas test readings are the EGR Cooler (is there enough exhaust pressure?) and the charge air cooler.

There's a diagnostic tester based procedure for testing for EGR leaks in section 5.7 of the workshop manual I came across during during the repair. I'm not sure how this works but I'm going to try that once I've gotten it running again. There's also a procedure in section 2.5 for the charge air system but it doesn't seem like a very robust test (you maintain a constant 0.5bar of air pressure in the unsealed charge air circuit and use a manometer to ensure pressure in coolant tank doesn't rise by >0.051bar). I'm going to pressure test the charge air cooler directly via its coolant inlet and outlet points this weekend before refilling the coolant circuit. I also planning to do the same with the EGR cooler. The pressure test I previously performed at 1.5bar on the entire coolant system didn't show any leaks but it's worth doing before I replenish the coolant.

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That is correct, presence of exhaust gases in the coolant can be caused by head gasket, EGR cooler and charge air cooler.

So I got the car back on the road yesterday, a week later than planned after some additional dramas that required some parts to be ordered in (unrelated to coolant issue, the car just hates me). I took it on a 35km test drive yesterday after filling and bleeding the coolant system and I had no dramas other than a warning message that may indicate a possible faulty oil level and temp sender.

However, I drove to work this morning (~50km commute mostly highway @ 100km and 80km), I had no recurrence of the temp sensor error, but when I checked the coolant at work I could clearly see that I'd just blown coolant from the cap again. I don't believe the car did a DPF regen during the drive, I stopped at traffic lights 5 or 6 times and the start/stop system turned the engine off each time, I didn't hear anything that would indicate a regen.

I suppose it's possible it's just some trapped air working its way out of the system, but I'm not holding my breath. I'll continue to monitor it, but I'll probably try replacing the heater matrix next if the problem persists.

Shocks, sorry to hear that. Maybe it just got some air out. But, your car does blow out out of the cap or ar the overflow? (That little hole under the coolant tank).

minu94 said:

Shocks, sorry to hear that. Maybe it just got some air out. But, your car does blow out out of the cap or ar the overflow? (That little hole under the coolant tank).

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I've never actually seen it coming out, just the aftermath, it seems to only occur when I'm driving. I have always assumed it comes from the cap because there's always a small amount of coolant pooled around the cap and on the engine mount bracket. I just took these pictures ..

https://imgur.com/a/EpeITB2

shocks said:

I don't believe the car did a DPF regen during the drive, I stopped at traffic lights 5 or 6 times and the start/stop system turned the engine off each time, I didn't hear anything that would indicate a regen.

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So VCDS tells me otherwise, the car did a regen 58.5km ago which means it did a regen 8km before the end of my commute this morning. I didn't have my laptop earlier to check this but hopefully I've found the smoking gun. As I said in my first post here, I wish I had found this forum before I ripped my engine apart to replace the head gasket

Also, minu94, yes, your absolutely right the coolant is probably going out the bottom vent with some also working its way past the threads of the cap. I only just had a really good look at it now, it's obviously a safer way to divert hot coolant once the pressure relief in the cap is activated.

I have also performed a chemical gas test, technically a pass as it didn't go green or yellow, but it didn't stay deep blue either. For comparison, on my 2.0TDI Passat it stays deep blue, zero change whatsoever.

Also shocks, you can use an app for Android (if you have one), called VagDpf. You can use it with a bluetooth obd adapter and you can see in realtime if the car is in active or passive regeneration. So I guess there is absolutely no change since you changed your head gasket.
Also, your car used or does this only at higher speeds/loads or it doesn't matter?

thanks minu94, I'm already on to that one, I downloaded it on Monday but unfortunately my old OBDLink Bluetooth from 2011 doesn't work with the app. I've ordered a cheap ELM327 dongle online so I should have this app up and running by tomorrow.

So I'm pretty confident the coolant losses are directly related to the clogged heater core and DPF regen issues everyone else is having. After confirming the DPF regeneration on Monday I ordered the replacement core, picked it up yesterday and installed it last night. The old core is definitely partially blocked, I could tell just by blowing air through it and the new one. Also, I checked the vent temperatures and sure enough there was a 10degC difference between passenger side and drivers side. This reduced to less than 1 degree after I installed the new core.

With respect to the headgasket, who knows, I was definitely getting exhaust gas in the cooling system, a lot judging by some of combustion gas test results I was getting (some tests went instantly green and one even went yellow). I suppose in theory the EGR Cooler could have a leak but how is there enough pressure on the suction side of a turbo to push that much gas into the coolant system? The switchable water pump I replaced along with the timing belt change seemed to be sticking, It could be that this was sticking in the off position causing excessive heat in the engine block which compromised the gasket seal.

Anyway, hopefully the heater core solves the remaining issue for now. I’ll update again if it doesn’t.

thanks minu94, I'm already on to that one, I downloaded it on Monday but unfortunately my old OBDLink Bluetooth from 2011 doesn't work with the app. I've ordered a cheap ELM327 dongle online so I should have this app up and running by tomorrow.

So I'm pretty confident the coolant losses are directly related to the clogged heater core and DPF regen issues everyone else is having. After confirming the DPF regeneration on Monday I ordered the replacement core, picked it up yesterday and installed it last night. The old core is definitely partially blocked, I could tell just by blowing air through it and the new one. Also, I checked the vent temperatures and sure enough there was a 10degC difference between passenger side and drivers side. This reduced to less than 1 degree after I installed the new core.

With respect to the headgasket, who knows, I was definitely getting exhaust gas in the cooling system, a lot judging by some of combustion gas test results I was getting (some tests went instantly green and one even went yellow). I suppose in theory the EGR Cooler could have a leak but how is there enough pressure on the suction side of a turbo to push that much gas into the coolant system? The switchable water pump I replaced along with the timing belt change seemed to be sticking, It could be that this was sticking in the off position causing excessive heat in the engine block which compromised the gasket seal.

Anyway, hopefully the heater core solves the remaining issue for now. I’ll update again if it doesn’t.

Shocks - minu94 beat me to it.

The Carista OBD Bluetooth adaptor is very good and can be bought for about GBP15 (look on Amazon)

I recently used VagDPF (GBP3.30 from Play Store) and it's really helpful. I also got the Carista app on free trial for 30 days so I tweak a few settings on the car.

I got loads of really useful help on this and another forum and narrowed it down to blocked heater matrix causing a coolant blowout/blowback directly after a DPF regen. The app helped me see that in real time and check coolant just after the regen had finished.

I had a silica gel expansion tank and couldn't see any sign of the baggie. Fitted a new one without bag last week. Also noticed my tank cap was `rattling` so maybe that wasn't helping. New lid also fitted. Did a DPG regen and coolant everywhere! At least it was something else off the list.

Also tried to replace coolant sensor on the block but that was impossible due to it being held in place by a bracket that runs under the engine (it was meant to be a 5 min job).
Gave up in the end - the garage can do it.

I removed and cleaned my matrix on Monday. Fair amount of scale and debris came out but no real goop (silicant). Initial hose pipe and blow test show reduced flow though. Lots of hot water, dishwater tab, de-scaler bathroom spray etc and it was much better. Put it back in and it's better but still have a 10 degree difference on left and right heaters (it's a LOT better than it was). I have a new one on order and will fit that this weekend.

I also have an issue with my thermostat/water pump that are effectively unrelated (I believe), as the car it overheating a bit. It did distract me a bit from the matrix issue. I now expect it to be the sticky switchable water pump or thermostat. A cambelt/pump/stat change next week will sort that. That will also allow a coolant change and I'll be able to see how much gunk is/is not in the system.

One of the things with the car that I learnt is that it has 3 cooling systems. The one for the EGR includes the heater matrix and head and warms up first when you start the car. This is meant to allow faster heat in the cabin and reduced emissions on start up etc. The main cooling system covers the main block and includes the radiator. This is only active once the car fully warms up and the stat opens up and the radiator gets used.

So - a blocked matrix doesn't really affect the main engine cooling and therefore you can cook your coolant (EGR/DPF regen) but still have a perfectly functioning cooling system (pump & stat).

You also have the charge cooler on a seperate circuit as well. That is why people say that a full coolant flush involves 3 different circuits. Well done VAG.

Theoretically, the main cooling system (block, pump and rad) are less prone to blockages due to their size. The smaller units (EGR cooler, pump, matrix & charge cooler) and associated pipework are more prone to reduced flow/blockage. An issue with your matrix can ultimately influence other parts/pipework but hopefully not.

Although we all seem to have similar issues, with the common denominator being the heater matrix, some of us may need to look at other areas as well.

I'm confident that a new matrix will solve the cabin heater and regen blow back issue. If not, I'll be looking at the EGR cooler and heater support pump.

I've not had access to VCDS yet but will when it's at the garage next week. I did get hold of a laser IR thermometer yesterday and that was really helpful. I can't access my coolant hoses that easily and a quick check with that showed my rad was cold, as was the main hose into it. Not good. Hopefully the cambelt/pump/stat change will sort everything out.

So - you can change a lot of stuff and a DPF blow black is not necessarily sign of a coolant, pump, stat or head gasket issue. It just makes it seem that way and possibly why so many garages go down that route.

Not sure how the exhaust gas thing tiues in. I will be testing mine for exhaust gases at the weekend, although I think I'd rather not.

I gained so much knowledge about this now and I'm really hoping it will be solved next week.

Shocks - get that app. It's really helpful! Look forward to positive news.

BillyCool, hopefully you'll sort it out with the new matrix. A VCDS type diagnostic tool is a must if you want to do this stuff yourself, if you don't want to pay that much OBDEleven is another good option. I've also been using VW ODIS (with VAS5054A) as the guided functions and test plans line up nicely with the VW Wookshop Manual instructions. I find it a bit clunky and slow though.

With respect to the comment you made about DPF blowback, I personally don't believe this is likely to introduce exhaust gas in the coolant system. Also, I independently pressure tested my Charge Air Cooler and EGR Cooler when I had the engine torn down and the cooling system dismantled. I tested each with air to 1.5 bar and observed no pressure drop after 15mins. I could be wrong, but I don't think the DFP and Exhaust system would produce a back pressure of >1.5bar. I didn't want to test at a higher pressure as 1.5 bar is the cooling system test pressure specified by VW and I didn't want to go any higher. Given the very small volume of air I was using, any leaks would show up pretty quick.

Of course for me the positive combustion gas tests were the reason I thought I had a bad headgasket, I hadn't come across this forum when I made that call, but I would of course have replaced the heater core before trying anything else had I known. Without the knowledge of the blocked heater core / DPF regeneration scenario it's logical to think leaking combustion gas via the head was a prime candidate in this case. Some claim this would result in ejected coolant every time you start the engine but this isn't necessarily the case, things can fail progressively and under different temperature and conditions.

The thing that surprises me it that VW haven't issued a bulletin on this heater core/ DPF regen issue as there seems to be a fair few examples of people here who have had head gasket and even new cylinder heads installed by VW under warranty.

An update since replacing the Heater Core, I've traveled about 750km and the car has performed 3 DPF regenerations with no loss of coolant. Hopefully this is the last of this particular problem, at least until the core clogs up again which I sure it inevitably will.

Great to hear that shocks. I guess I also had narrowed it down to being the heater core. One way of minimising the loss of coolant after a regen is to turn the heat in the car at maximum. That is something that seemed to help.
Also, did you perform any kind of cleaning of the cooling system?
LE: What heater matrix did you get?

minu94 said:

Also, did you perform any kind of cleaning of the cooling system?
LE: What heater matrix did you get?

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Other than the fact that I completely emptied the old coolant during the teardown I did, then no. I put 8 litres of fresh coolant in this car 2 days before I pulled out the heater core so virtually all the old coolant had been removed. I don't think the amount of contaimination that remained would be worth worring about. The approx. 250ml of coolant I removed from the old core and feed pipes (using compressed air via the firewall hoses) was crystal clear. Flushing the coolant system and refilling seemed to be a needless waste of money. These cores didn't clog up overnight and I don't plan on owning this car for another 120K.

See my previous post on the part number I used, I got a genuine part from VW Parts and it's the newest version of that particular one. The core you need depends on the manufacturer of the overall airconditioning system in the car. The piping connections are different for the two different OEM's.

@shocks, have you checked the coolant passages from the cylinder head? I have heard also about some issues with the coolant passages being blocked

minu94 said:

@shocks, have you checked the coolant passages from the cylinder head? I have heard also about some issues with the coolant passages being blocked

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I thoroughly inspected the cylinder head and engine block including the galleries and passages. Some are quite narrow but there were no signs of any blockages. In fact the passages on the head were very clean, even before I cleaned it ... https://imgur.com/a/TwwvjkZ

Hello everyone.

I'm here because a problem with the disappearing coolant during DPF in my G7GTD.
I have read this thread, and learned a lot, thank you, great work guys.

But I have 2 questions.

1- Don't you think that the problem may be the pump V488 (7) on Pic.1 which due to some defect is insufficiently pumping fluid?

https://imgur.com/WxOjhgd

or,

2- Do any of you have parking heater or heating support in your vehicle?
If so...
Maybe it's a faulty V55 Pic.2 pump in the heater system.

https://imgur.com/exkiC7o

Because in my case there are no errors in the Engine, but in Parking heating I have an error of a damaged V55 pump.

Regards Kamil.

We don't have the parking heater in the US cars. This would be something someone would have to add on their own I think.

Kamilecki166 said:

1- Don't you think that the problem may be the pump V488 (7) on Pic.1 which due to some defect is insufficiently pumping fluid?

Click to expand...

It's possible but much more likely to be the matrix, it seems to be the restriction in the matrix which is forcing coolant under pressure back into the reservoir via the small coolant overflow line in most cases, I believe.

If you want to test the electric coolant pump for this circuit just remove the inlet coolant line at the firewall (quick coupling) that goes to the matrix and place it in a bottle. Turn the ignition on and you should get a good strong flow once that pump turns on.

Edit: Dont Start the engine!! You just have to turn the ignition on. Also, do it when the coolant is cold.

So I have had this as well. Seat Leon 2014 2.0 TDI 150 70,000 miles. Symptom: No heating in cabin after driving for an hour on motorway. Coolant seeping out of expansion tank. Had cambelt and water pump changed as it was due anyway.

Dealer said heater matrix but wanted £ 910 to change it. So I sought opinions from other car repair shops. One said it was head gasket or cracked cylinder head. He attempted to demonstrate that with a combustion leak tester – you’re looking at the lower chamber nitwit! I hired a combustion leak tester and saw no colour change in upper chamber! I asked Hellfords how much to change the heater matrix, £ 420. Any warranty? No.

Then I read the workshop manual and found it’s quite labour intensive to change the heater matrix properly; drain, flush three times, fill, bleed. All using VAG tools and computer. I did go with the dealer because they have two years warranty parts and labour. They said they saw a lot of debris and sludge all over the cooling system.

Annoying to have to pay £ 910 on a six year old car, but I guess not too bad in the whole scheme of things – other cars of the same vintage appear to have had much larger problems. Especially diesels.

The dealer claimed it’s the silica bag melting – could be but I have seen QA problems with the heater matrix manufacture in the early days of the MQB platform mentioned as a potential cause on other VAG forums.

Nevertheless I think this is a generic MQB problem and something VW, Audi, Seat and Skoda owners will all suffer over time – the dealer said they are changing many. I think we should all put together a UK class action lawsuit. I can take the initiative, but will require lawyers so I suggest crowdfunding, maybe £ 10 for each of you?

Tjockhult said:

So I have had this as well. Seat Leon 2014 2.0 TDI 150 70,000 miles. Symptom: No heating in cabin after driving for an hour on motorway. Coolant seeping out of expansion tank. Had cambelt and water pump changed as it was due anyway.
Dealer said heater matrix but wanted £ 910 to change it. So I sought opinions from other car repair shops. One said it was head gasket or cracked cylinder head. He attempted to demonstrate that with a combustion leak tester – you’re looking at the lower chamber nitwit! I hired a combustion leak tester and saw no colour change in upper chamber! I asked Hellfords how much to change the heater matrix, £ 420. Any warranty? No.
Then I read the workshop manual and found it’s quite labour intensive to change the heater matrix properly; drain, flush three times, fill, bleed. All using VAG tools and computer. I did go with the dealer because they have two years warranty parts and labour. They said they saw a lot of debris and sludge all over the cooling system.
Annoying to have to pay £ 910 on a six year old car, but I guess not too bad in the whole scheme of things – other cars of the same vintage appear to have had much larger problems. Especially diesels.
The dealer claimed it’s the silica bag melting – could be but I have seen QA problems with the heater matrix manufacture in the early days of the MQB platform mentioned as a potential cause on other VAG forums.
Nevertheless I think this is a generic MQB problem and something VW, Audi, Seat and Skoda owners will all suffer over time – the dealer said they are changing many. I think we should all put together a UK class action lawsuit. I can take the initiative, but will require lawyers so I suggest crowdfunding, maybe £ 10 for each of you?

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Your dealer seems better-informed than many that have been reported here. After reading about this common problem in this forum, I proactively changed my coolant reservoir before its silica bag could rupture. The new reservoir appears to use a different kind of silica bag that is presumably more durable over time. Part# 5Q0121407T, Engine Coolant Reservoir, $9.96 from VW Parts Warehouse. I renewed the reservoir cap O-ring at the same time: Part# 1H0121687A, Seal. Reservoir. Cap. Coolant. Engine, $2.51. Simple job if one uses a turkey baster to remove the coolant prior to disconnecting the reservoir hoses.