Coolant loss from tank on motorway journeys or high speeds

BillyCool

Active Member
Jan 16, 2020
655
249
Leicestershire, UK
These are the notes I've taken off various forums to replace the matrix. The You Tube video was helpful, albeit on an Octavia. They are all slightly different.

I have got some photos as well if that helps.

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Replace Heater Matrix

The part number for the heater core is 5Q0819031B - Denso or Valeo??

5Q0 819 422 A for Valeo and 5Q0 819 422 for Denso

Or Nissan 73980


Heater unit diagram

https://nemigaparts.com/cat_spares/etka/seat/le/754/819200/


I’ll be changing the matrix with fitting kit, new expansion tank, new g13 coolant with distilled water 50/50 ratio.

All done, took about 3 hours including finding tools and a test drive as it wasn't heating up with no load on it. All back together and no leaks at full temperature.

Got the heater matrix out without removing the glove box, just need to remove the air distributor and the blower motor to get enough clearance.

Got loads of scale out as soon as the lower pipe came off. Ordered a new heater matrix yesterday morning and it arrived by lunchtime knowing that I could return it if that wasn't the issue.

You don't even need to remove the blower motor. Just one bolt holding on the air distributor which you can get out of the way fairly easily.
Reckon you'll have the new one fitted in under an hour.

As mentioned, I had a go at driving the car at high revs for a while to raise the water pump pressure around the system.


Upper bulkhead hose is hot and the lower one only warm-ish so looks like blocked heater matrix.

https://forums.seatcupra.net/index.php?threads/aircon-and-heater-doesnt-work.432793/page-4

Extra images: http://forums.tdiclub.com/showthread.php?t=483783&page=11

When refitting, I realised that I really didn't need to pull all that crap out to get to it. You can literally get it out by:
Draining coolant
Removing:
2x heater matrix hoses in the bulkhead
1x Torx screw on 'skirt' under the centre console
1x Torx screw on the lower pipe clip
1x Torx screw behind the glovebox (just flip it down as you would for a pollen filter change) to remove the air duct for more access room
2x Torx screws for the flap holding the matrix in place

Octavia video:

And that is literally it! On reflection, I honestly believe the draining, removing/refitting of the matrix and filling back up with fluid could be done in under 2 hours. And that is by me - a ham-fisted DIY'er. How these garages have taken days and even weeks to do this job, is beyond me!

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minu94

Active Member
Nov 4, 2019
17
2
So, today I removed the old heater core and got the new one installed. Also changed the coolant. What I found home, whilst putting water with pressure inside the old heater core surprised me, but not in a good way. The next few days I will try to go on a longer trip to see if the coolant still gets out.
Pics:
https://ibb.co/r6DXF2t
https://ibb.co/dPKGgpv
LE: There were more debris than seen in the pic.
Also, before trying to clean it, water was barely coming out. After some minutes of attacking the heater core from both sides, it started to flow more easily. I have videos of that if someone is interested
 
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BillyCool

Active Member
Jan 16, 2020
655
249
Leicestershire, UK
So, today I removed the old heater core and got the new one installed. Also changed the coolant. What I found home, whilst putting water with pressure inside the old heater core surprised me, but not in a good way. The next few days I will try to go on a longer trip to see if the coolant still gets out.
Pics:
https://ibb.co/r6DXF2t
https://ibb.co/dPKGgpv
LE: There were more debris than seen in the pic.
Also, before trying to clean it, water was barely coming out. After some minutes of attacking the heater core from both sides, it started to flow more easily. I have videos of that if someone is interested

OMG - that's terrible! No wonder it was blocked.

Your new matrix should be so much better.
 

minu94

Active Member
Nov 4, 2019
17
2
Yes, now I almost get 70 degrees Celsius out of the vents, I finally have back my heat atleast:)) hopefully I have also solved the problem regarding the coolant blow out. Will check and come back with feedback.
 

BillyCool

Active Member
Jan 16, 2020
655
249
Leicestershire, UK
Yes, now I almost get 70 degrees Celsius out of the vents, I finally have back my heat atleast:)) hopefully I have also solved the problem regarding the coolant blow out. Will check and come back with feedback.

Good to hear. Ther best I could get with my old matrix was about 50 degrees. I'm looking forward to fitting my new one.

Do you have VAG DPF to check when your car is doing a regen?
 

minu94

Active Member
Nov 4, 2019
17
2
Ah, yeah. I will check that after my first regen. Also, my car did blow out coolant at sustained high speeds, over 110 km/h, not only during regens.
 

BillyCool

Active Member
Jan 16, 2020
655
249
Leicestershire, UK
Ah, yeah. I will check that after my first regen. Also, my car did blow out coolant at sustained high speeds, over 110 km/h, not only during regens.

Really? Mine only seemed to blow coolant after a regen and it just happended to be on motorway runs.

Keep us posted on how it gets on.
 

minu94

Active Member
Nov 4, 2019
17
2
Today I had a combination of regen with speeds of 110 km/h sustained and it did not blow out any coolant. Fingers crossed!
 
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Reactions: BillyCool

minu94

Active Member
Nov 4, 2019
17
2
Head gasket now, hopefully I will find somewhere to take it to, given the outbreak of Coronavirus.
 

minu94

Active Member
Nov 4, 2019
17
2
That is the only option that I have. I replaced EGR cooler, chargecooler, some hoses and the heater matrix...
 

minu94

Active Member
Nov 4, 2019
17
2
I also replaced the coolant reservoir along with the cap. There is another guy on another forum that resolved the problem with the head gasket. Also, I checked my coolant for exhaust gases before I changed the chargecooler which tested positive, but I thought that was because on some very small cracks on my chargecooler. I’m pretty much fed up with this cars cooling system. It is way too complicated.
 

BillyCool

Active Member
Jan 16, 2020
655
249
Leicestershire, UK
I also replaced the coolant reservoir along with the cap. There is another guy on another forum that resolved the problem with the head gasket. Also, I checked my coolant for exhaust gases before I changed the chargecooler which tested positive, but I thought that was because on some very small cracks on my chargecooler. I’m pretty much fed up with this cars cooling system. It is way too complicated.

Totally agree. The cooling system makes it hard to diagnose the fault and then fix it.

Let us know if you get the HG sorted and whether that fixes the issue.
 
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