Coolant and heating issues

[caledonian]

Hey Guys,

Got a low coolant warning this morning on my 2017 2.0 tdi 184 FR it was -5°c.

On my way to pick up some coolant I noticed the heaters weren't working very well. After topping up the heaters got worse cold on the passenger side warmish on mine, but only at lower fan speeds and temps if I put it on Hi it cooled right down.

After 10 -15 minutes of driving the temp drops altogether regardless of settings.

I've read as much as I can on here (great info) and most likely culprit is a clogged heater matrix from the silica bag. Was wondering if I could have caused an air lock somehow and would that cause similar problems?

Do you think the low coolant (probably down to freezing temperatures) is coincidental? Also is it safe to drive the car about with a blocked matrix? Going to try and get it looked at next week as Im ham-fisted and will likely break something trying to fix it myself.

 

[BillyCool]

Quick answer is that if it is a blocked heater matrix, the car basically boils your coolant during a DPF regen (as the blocked matrix stops it cooling effectively). The overpressure (and some coolant) exit via a release valve in your header/expansion tank lid. As the system is pressurised when hot, you do not get a low coolant warning until the next time you drive it (everything cools down and your coolant then drops below minimum).

You can still drive it, but you will probably loose a bit of coolant every time it does a regen and you'll have cold air in the cabin.

SEAT quote about £1200 to fit a new one as their tech docs require the dash to be removed. Someone else got an Indy to do it for about £400 to £500. Ideally you want to change the header tank for one without the silicate bag and also flush out as much old coolant as you can. As well as the potential goop from the silicate bag, there has also been found casting sand blocking things up.

You can do it yourself - the matrix is about £85 and 3 hours of your time, with the help of a You Tube video and folk on here. As you say, if you're a bit `clumsy`, you may need to pay someone else to do it.

Ref it being an airlock - less likely as the system is meant to self-bleed. Not impossible but the symptoms suggest a blocked matrix.

Hope you get it sorted.

 

[caledonian]

Billy thank you for that great info, spoke to my independent local garage just there and they confirmed exactly what you are saying.

Said they've done a few but they dont have the specialist kit to fully flush the system. They are happy to flush what they can and fit a new matrix, but without the full flush they can't guarantee it won't block up again. I'm happy to give that a shot anyway so booked it in for Wednesday. Will let yous know how I get on and the cost. Thanks again for the detailed info, much appreciated

 

[BillyCool]

No problem. Generally, only VAG specialists have the kit to fully flush the system - there are a few one way valves and things need to be done in a certain order. It isn't critical to have it done.

What you can ask them to do is just drop out as much coolant as possible. I had my water pump and thermostat & housing replaced and that helped. Some people suggested running deionised water through a couple of times as well. I'm sure your garage will do a good job. The engine actually has 3 coolant systems and the heater matrix/EGR cooler one is very small. Mine was never professionally flushed and 4 years later it's still doing okay.

Once it's done you usually get a little bit of air in the system. You just drive it and top up the coolant next day when it's cold. Mine needed 2 or 3 top ups and was all good.

Are you getting a new header tank without the tea bag as well?

 

[caledonian]

Again, thank you Billy its reasuring to know you have been OK without a full flush. I'll talk to them Wednesday morning and see what they say about the header tank, I've seen guys on YouTube pulling them out with needle nose pliers, not sure if that's best practice or not .

Not had many issues with the car over 2 and half years but in the height of summer there the airccon went and I needed a new condenser, now it hits -5 the heating matrix has gone so the car definitely has a sense of humour it appears

 

[BillyCool]

If the tea bag is intact you could remove it, although for the cost of a header tank (c.£40) and it takes 10 mins to swap them out, you could argue just fit a new one. The other potential issue is the pressure release valve in the lid can be a bit tired with all the overheats and ideally could be replaced. If you take the lid off and shake it, if it rattles, it's a bit worn and may not keep the system pressurised. Not essential but some people do replace them (preferable to replace the whole unit than just the lid).

My car has had several things need replacing - seems to be a common theme! (not a condenser though).

Let us know how you get on.

 

[SuperV8]

Not all tanks with mit-silicate have the 'tea bag'.
Mine had mit-silicate - and the repository was built into the tank so not removable - You know which one you have as with a constrained repository you can't see anything looking into the filler neck, but you can see the 'tea bag'! I'm not sure this type can leak - but changed mine anyway for peace of mind.

My pressure cap was weak - easy to test - blank off ports on the tank and pressurise with a bike pump and gauge. Supposed to be something like 23psi - but mine let off at something like 10psi!

 

[caledonian]

Thanks again for the info guys, got the car back today, the guys haveremoved the bag and flushed what they can from the system and replaced the Matrix. Cost £350, not too bad compared to some I've heard, the heating is nice and hot again which is good considering it was -5 here today.

Only issue is there's a sloshing sound now when I turned the ignition off, I'm guessing that's air in the system, will that sort itself out? I read somewhere these are self bleeding?.

 

[BillyCool]

Thanks again for the info guys, got the car back today, the guys haveremoved the bag and flushed what they can from the system and replaced the Matrix. Cost £350, not too bad compared to some I've heard, the heating is nice and hot again which is good considering it was -5 here today.

Only issue is there's a sloshing sound now when I turned the ignition off, I'm guessing that's air in the system, will that sort itself out? I read somewhere these are self bleeding?.

That is a really good price!

Ref the `sloshing` - yes, it will do that for a while. Check coolant every morning when it's cold and top up as needed. After being driven a few times and topped up it should sort itself out. It does self bleed.

Bet you're glad to have that warm air again!

 

[caledonian]

That is a really good price!

Ref the `sloshing` - yes, it will do that for a while. Check coolant every morning when it's cold and top up as needed. After being driven a few times and topped up it should sort itself out. It does self bleed.

Bet you're glad to have that warm air again!

Was sweating on the way in for nightshift tonight!

Thanks again for the detailed info, much appreciated

 

[Danielr89c]

Hi, I’m having the same issue. Small background story to my car... the heating was weak as anything and basically stopped working, I googled the issue and it was pretty obvious it was going to be the heater matrix as we all know they’re common to go on VAG cars. I took it to a VAG specialist and they confirmed the heater matrix and I had it replace (For a small fee of £1,100 🫣) since I’ve had the car back the heating works brilliantly. However I have had to top up the coolant 3 times in the last month (I got it done about 6 weeks ago and since then it’s gone through 1ltr of coolant) initially I thought it just needed to settle down as the same happened when I had the cam belt and water pump done. However I was a little concerned as one litre Is a lot in 6 weeks. I took it back to the same garage today and they did agree that it shouldn’t be using that amount however they now think the charge cooler has gone and that’s where the coolant is going. So long short im looking for advice if anyone else has had the same issue since replacing the heater matrix. I don’t really feel that the charge cooler has gone as this coolant issue has only started to happen since I got the car back after having the matrix replaced, before this it was barely using any coolant (topped up about 1-2 times a year if that).

 

[caledonian]

I had to top mine up for around a week afterwords I wouldn't say a litre but it did take a good amount. £1100 seams a lot compared to what I paid. I'd definitely get a second opinion. The guys on here are pretty clued up on this stuff so hopefully one of them can point you in the right direction

 

[Danielr89c]

I thought that too. I did speak to two specialists near to where I live and they were pretty much the same as each other. I was under the impression it would be no more than £500-600 according to people on here who have had it done. I was a little surprised when the quotes came out at £1,100 as a main dealer isn’t far off of that. They have told me that if it the charge cooler causing the issue that’ll be another £1,200!! I had to sit down after that I am struggling to believe them as I had no coolant lose issues even when I had the issue with the matrix so it just seems a huge coincidence that they remove a lot of the cooling system and now I have this issue.

 

[BillyCool]

Some people got an Indy to do it for less than £500, which is good. I suspect that they do not follow the SEAT manual and remove the whole dash (SEAT quoted me £1300 and I politely declined). If other places follow the book, £1000 seems to be the going rate. I did mine myself in 3 hours and $90 for the matrix. At least if it goes wrong I can blame myself.

It does sound like more coolant is being used than should be. If you can get under the car and remove the undertray, are there any obvious witness marks of a small leak? Thermostat housing, hoses, pipes etc? You could take off the access panel in the passenger footwell and see if there is any damp below or around the matrix. I would expect you to smell it if it was to be fair.

It could be `coincidence` that your charge cooler is failing. Hard to say. I've not heard of it being linked to replacing a matrix. Might just be bad luck and it's hard for you to prove otherwise.

I assume they've ruled out head gasket issues?

I wish you luck sorting it out.

 

[Danielr89c]

I took the car back the same garage today and they did a pressure test on it and said that there is no obvious leaks that they could see. However they slightly contradicted themselves as they said a pressure test for 2 hours isn’t enough to be sure of minor leaks which could be related to something they have done when they replaced the matrix. They have recommended that I go back and leave it for them to do a 8 hour pressure test to see if that shows anything. I do around 300 miles a week and after I got the car back after having the matrix done I have had to top up the coolant around once a week (roughly, may be say every 10 days). After reading some other posts it does sound like it may just need to settle down after having the matrix done. I might be being syndical but like I said this issue was present before i took the car in for the matrix issue.

 

[Danielr89c]

Sorry to answer your question yes they have ruled out head gasket

 

[Walone]

I thought that too. I did speak to two specialists near to where I live and they were pretty much the same as each other. I was under the impression it would be no more than £500-600 according to people on here who have had it done. I was a little surprised when the quotes came out at £1,100 as a main dealer isn’t far off of that. They have told me that if it the charge cooler causing the issue that’ll be another £1,200!! I had to sit down after that I am struggling to believe them as I had no coolant lose issues even when I had the issue with the matrix so it just seems a huge coincidence that they remove a lot of the cooling system and now I have this issue.

Personally, I'd avoid that 'specialist' like the plague! See the attached PDF taken from Seat manual for changing the heat exchanger/matrix.

 

[SuperV8]

Personally, I'd avoid that 'specialist' like the plague! See the attached PDF taken from Seat manual for changing the heat exchanger/matrix.

You don't need to detach anything in the engine bay when you change your heater matrix.
Just have a small plastic tray ready to catch less than 500ml coolant when you detach the hoses from the heater matrix. The coolant doesn't continue running.

The 'book' time for a heater matrix "Remove/refit the heat exchanger RHD" is 1.9h - don't know how these garages are charging £500-1000+

 

[SuperV8]

I took the car back the same garage today and they did a pressure test on it and said that there is no obvious leaks that they could see. However they slightly contradicted themselves as they said a pressure test for 2 hours isn’t enough to be sure of minor leaks which could be related to something they have done when they replaced the matrix. They have recommended that I go back and leave it for them to do a 8 hour pressure test to see if that shows anything. I do around 300 miles a week and after I got the car back after having the matrix done I have had to top up the coolant around once a week (roughly, may be say every 10 days). After reading some other posts it does sound like it may just need to settle down after having the matrix done. I might be being syndical but like I said this issue was present before i took the car in for the matrix issue.

These are quite complicated cooling systems with lots of one way valves -
You could ask how they have pressure tested it? I doubt just pressurising the two pipes by the header tank (the easy way) would give you a meaningful result if that's all they have done.

Unless it was chronically under filled when they did the matrix, this seems to me like a lot of coolant to add for just some trapped air from a heater matrix swap? Did they also flush the cooling system - if yes more chance of more trapped air.

You should be able to check around the cap if coolant is being expelled from the cap/tank as it will look wet under the tank.

Keep an eagle eye on your coolant level after each journey.
If it gradually drops over many heat cycles I would suspect a leak (either external/visible or internal and burnt in the engine which may give you white smoke out the exhaust) -
external = coolant pump/heater matrix ports/O-ring but that would give you wet carpets), heater matrix pipes on bulkhead in engine bay/ pipes.
internal = egr cooler/charge air cooler/headgasket.

If the coolant stays level over several journeys and then suddenly drops, this is aligned with symptoms of an issue with your heat exchanger circuit - check your cap pressure relief (mine was weak - about half what it should hold) or maybe your pump isn't working - you have a micro electric pump on your heat exchanger/egr cooler circuit which should run after your engine is switched off - if this doesn't run it could locally boil expelling coolant out your header tank cap.