# Misty windows and slow coolant leak - Heater matrix leaking?



## John-H (Jul 13, 2005)

*How to fix leaking bulkhead couplers*

I had to change the O rings on the heater matrix bulkhead couplers yesterday. They had become flattened and were not sealing properly. I was getting occasional wiffs of vapour coming through the air vents and a film residue on the Windows that was difficult to clean off. This is antifreeze residue and probably not good to breathe in either. The other symptom is a slow loss of coolant with no obvious leak.

*This fix costs pence but the fault could easily get misdiagnosed as a leaking heater matrix at much expense!*

I'd seen this with my S3 but the O rings were also obviously worn and disintegrating. The TT's 28 mm OD O rings were showing absolutely no signs of wear and looked perfect apart from their shape which had a flat on the inner and outer edge measuring 3.2 mm across flats but 3.7 mm front to back.

This makes me wonder what will happen to all the push fit plumbing solutions being installed into houses. Good stored up work for plumbers and decorators after several years I think :wink:



















Fixing or changing the couplers is simple. You don't need to remove anything major to gain access which you gain from the engine bay behind the engine high in the middle the bulkhead..

You need to cut a cable tie and unclip the silver heat shield wrap around the hoses. A pair of pliers for the hose spring clips will remove the hoses but it might be easier to pull the couplers off the heater matrix first as you can pull the hose to do it.

If you are only changing the O rings you can leave the couplers clamped into the hoses.

To disconnect the couplers from the heater matrix, pull the spring clip back with a screwdriver. They should retract down. Feel underneath with a small flat bladed screwdriver. The spring clip only retracts so far and locks expanded. Make sure you don't ping it off and lose it! See the pictures. The lower one shows the middle of the spring going across from one side to the other, under which you need to lever and also showing the spring sides that lock onto the matrix pipe. The top picture shows the side where there's a small groove that latches the clip wire end, expanded in the unlocked position.


















Then pull the coupler and it's off. Undo the hose clip if changing the couplers. Do one at a time so you don't mix up in and out but it probably doesn't matter.

The O rings can be removed from their internal groove with a small screwdriver or wire hook. You can keep the couplers on the hoses to do this as the pipes are flexible. Face them towards you and give them a clean with IPA and kitchen roll wiped round to remove any dirt. Push the new O rings into the grooves.

Lubricate the O rings with coolant for easy refitting of the couplers back on the matrix.

The couplers can be refitted with the spring clip engaged (it expands) or retracted which is easier but you need to press it back with a snap - simple


----------



## 3TT3 (Aug 30, 2014)

.. I gotta say John-H..and Im a big fan of your knowledge base compilation and the work needed!

My a/c and other related bits better keep workin good :lol: .I have spent a few pennies on other things .If those sort of components start playing up, I think Ill have to go the Clint Eastwood route "Play misty for me"


----------



## John-H (Jul 13, 2005)

Misty is playing a full season. Trouble is once this happens you inevitably get puddles collecting inside the aircon. The mist continues to come out and Steam up the windows with an oily sweet film even though you've fixed the leak. I've got to clean the windows every day. I'm wondering if it can be drained to speed things up?


----------



## John-H (Jul 13, 2005)

I'm going to have to see if I can drain the fluid trapped in there I think as there could be quite a bit to evaporate over weeks - that's how long my S3 took. Here are some pictures of a heater unit rolled over away from you 90 degrees at a time. I've marked the various features for reference.










The heater is dropped into this slot with the angled pipes poking through the bulkhead to the lower side of the picture.



















The matrix underside appears to have a bulge which could be identified from the foot well perhaps? Possibly a hole can be drilled to drain it and then a plug inserted to seal it :wink:










Heater matrix










Blower motor










You certainly don't want to have to replace the matrix so care needs to be taken. Replacement would involve taking the dash and centre console out and degassing the aircon etc.


----------



## hoss (Feb 17, 2010)

I have an 8n 3.2 with a matrix leak.
Unfortunately it doesnt seem to be the external unions, no leaks on the engine bay side. I dont see how those could cause cool inside anyway, it would have to get past the bulkhead seal.
I've got some of the lower dash trim off and theres coolant traces coming out of the heater box and onto the carpet.
If its a complete heater box removal (and re-gas) i might leave it to a dealer. Its a friends car and i just dont have time for that, plus i cant re-gas anyway.


----------



## John-H (Jul 13, 2005)

hoss said:


> I have an 8n 3.2 with a matrix leak.
> Unfortunately it doesnt seem to be the external unions, no leaks on the engine bay side. I dont see how those could cause cool inside anyway, it would have to get past the bulkhead seal.
> I've got some of the lower dash trim off and theres coolant traces coming out of the heater box and onto the carpet.
> If its a complete heater box removal (and re-gas) i might leave it to a dealer. Its a friends car and i just dont have time for that, plus i cant re-gas anyway.


Firstly, leaking coupler o-rings can cause a coolant leak into the heater matrix as that's actually what happened to my S3 and once the o-rings were replaced it eventually dried up although it took a while.

At moments of high pressure the coolant squirts out of the coupler in the direction of the heater along the surface of the pipes and through the bulkhead gasket which is only a loose fit on the pipes - so it gets inside. It can also go the other way but will likely drop down the back of the bulkhead heat shield so not obviously get into the engine bay.

It's worth a look at the condition of the o-rings. If one is perished I'd change it and give it a few weeks to see if it dries up.

As I say, my S3 was fixed by changing the o-rings. Alas the TT, with its slightly flattened o-rings was not saved by changing the o-rings. That eventually turned out to be an actual heater matrix leak - I was clutching at straws in this case - o-rings are usually resilient.

You can change the matrix without de-gassing the aircon as unlike the pictures above, the AC unit can be split by removal of clips in the middle, so the aircon half can remain undisturbed and the heater matrix in its half tilted forward and the matrix changed. It's still a big job:

viewtopic.php?f=2&t=1691186&p=8648538

It's all cured now, but so was my S3. I'd check your o-rings first.


----------



## hex (Nov 23, 2017)

Where did you source the O rings, and what's the spec on them?


----------



## John-H (Jul 13, 2005)

The size I mentioned at the top from measurement. The best value source I found was Farnell: 2135615

419 pieces in a kit for less than £10

http://uk.farnell.com/duratool/d01887/o ... dp/2135615


----------



## hex (Nov 23, 2017)

Cheers for that. I've the misting/smell issue and praying it'll be sorted by this treatment.


----------



## John-H (Jul 13, 2005)

hex said:


> Cheers for that. I've the misting/smell issue and praying it'll be sorted by this treatment.


Wishing you well. My S3 had crumbling o-rings that caused the same symptoms as my TT which only had flattened o-rings. The TT unfortunately had a leaking matrix whereas the S3 matrix was fine. It's certainly worth checking the o-rings and even if unsure, changing them. That's much easier than changing the matrix which might be the eventual pill to swallow.


----------



## hoss (Feb 17, 2010)

John-H said:


> Firstly, leaking coupler o-rings can cause a coolant leak into the heater matrix as that's actually what happened to my S3 and once the o-rings were replaced it eventually dried up although it took a while.
> At moments of high pressure the coolant squirts out of the coupler in the direction of the heater along the surface of the pipes and through the bulkhead gasket which is only a loose fit on the pipes - so it gets inside. It can also go the other way but will likely drop down the back of the bulkhead heat shield so not obviously get into the engine bay.
> 
> You can change the matrix without de-gassing the aircon as unlike the pictures above, the AC unit can be split by removal of clips in the middle, so the aircon half can remain undisturbed and the heater matrix in its half tilted forward and the matrix changed. It's still a big job:


I really dont think it is doing that in this case. Theres absolutely no trace of coolant deposit on the outside of the bulkhead around the unions. whereas inside i have a clearly visible pink residue from the heater box.
Good news about the A/C unit, thank you


----------



## PaulZR (Jul 30, 2016)

Hello all

I'm suffering from a slightly musty smell and occasional mist through the vents. Have acquired some replacement o-rings to see if this fixes the issue before I start removing the dash, but I cannot locate the bulkhead couplers. I don't suppose anybody has a picture of them in situ that I could use for reference?

Many thanks
Paul


----------



## John-H (Jul 13, 2005)

If you look at the back of the engine on the right as you look at it stood in front, above the turbo and to its right there are two rubber hoses disappearing into the bulkhead through the aluminum heat shield. You can't see the couplers very easily as they are behind this heat shield when coupled and you need to release them from the matrix and pull them back out still on the hoses. The hoses are also covered in a silver fabric heat shield with pop fasteners and there's a tie wrap holding the hoses in a pair together. The hoses come to the coolant plumbing on the end of the engine. Don't forget to release the pressure first.


----------



## PaulZR (Jul 30, 2016)

Thanks for the reply, John. Struggling with the air con in general but will add this to the list.


----------



## Psychobilly (Oct 19, 2019)

Had the misted up windows and smell in my '03 3.2 TT and all the local garages and Halfords wouldn't touch it. All said that it's a dealership job. Phoned local dealers who quoted £220 for the matrix and 4.7 hrs labour at £150 per hour. Job finally took their engineer 17.5 hrs! Their explanation was that the quote was for LHD vehicle. Fair play they charged me the £925 original estimate and as compensation for keeping the car so long, full valet and pumped up the air con. I pity the next one who goes there for the job though!


----------



## John-H (Jul 13, 2005)

Tell me about it. You need to take the dash off and the crash bar and split the climate control unit. Complete mess:










More details here:
https://www.ttforum.co.uk/forum/viewtop ... &p=8648538


----------



## StuartDB (Feb 10, 2018)

Blimey, at least it makes it easier to change the brake light switch


----------



## BenOfTheNorth (Sep 14, 2020)

I've just gone through this to see if it solves a leak I was getting - and so far it has (Need to go for a thorough drive though to be 100%).

The coolant was dripping from the left hand pipe onto the turbo/exhaust manifold causing a loss of coolant and also smoke where the coolant was being burned off.

After 30 mins of wrangling (I was worried about losing one of the clips!) I managed to get the pipes out and replaced the O rings on both - the left hand pipe had a significant difference, more so than the OP, so I think that was likely the offender.

If it turns out I'm still leaking I think I'm just going to have to replace the hose, but so far so good, thanks for the excellent guide, it's saved me a big garage bill.


----------

