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Coolant loss from tank on motorway journeys or high speeds

YKFR

Active Member
Jul 23, 2019
51
8
@YFKR, any news? Did you get it fixed or do you have the same issue?
Hi,

Yes, I got the problem fixed by replacing the heating matrix replaced. It was clogged up with tiny solid pieces of copper/bronze looking things. So I can only assume that the silicate bag had indeed burst inside my old tank.

So a full coolant flush and replacing the heating matrix was the fix for my car.

Hope this helps everyone who has had same problem with VAG cars.

Note: Anyone who has this repair attempted, do the full system flush/bleed first. Then put the new matrix in.
 
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minu94

Active Member
Nov 4, 2019
17
2
Exactly what I was thinking on doing. But do you have any idea about how the service flushed the system?
Also, in what order to do everything from start to end?
Many thanks for your fast response :D

LE: Put the new matrix in before filiing with coolant, or while the system is full with coolant? Also, bleed the system before or after changing the matrix?
 
Last edited:

RUM4MO

Active Member
Jun 4, 2008
6,240
446
South Scotland
Never having needed to do this, I would think that initially you disconnect the heater matrix flow and return pipes going through from the engine area to the cabin, then join these 2 pipes together, probably remove any thermostats and fit a mains water hose to the expansion tank and remove and replace one at a time other hoses to allow each section to get flushed out - possibly reverse flushing from one or both of the hoses to the heater matrix, while making sure any electric pumps are activated - seal the system up while still leaving the heater out of circuit and take the car for a run to fully warm it up and get the water flowing as it would normally do, repeat the opening and flushing and if necessary repeat the resealing and taking the car for a run until there is no evidence of debris circulating - then drain down entire system, replace heater matrix and all removed thermostats, refill with coolant and bleed.

Now just how much of that will a main dealer bother doing - time is money and your repeat visit will be welcome!
 

YKFR

Active Member
Jul 23, 2019
51
8
Because I got it done from a VAG specialist who only charged me £300, I can only assume that they got rid of the old matrix entirely, then ran the coolant flush multiple times. Until there was no sign of any solid materials. Once the system was fully bled. They must have installed the new matrix and then put new coolant in the system.

Also I asked them for my expansion tank to be flushed out, incase any silicate was left in there.

I wasn't there so I can't guarantee they 100% did it in that sequence. But it only makes sense and after it was done, I had a chat with the mechanic and he said he did those things. I told them what I wanted done first. Which was the coolant flush to begin with.

Hope this helps.
 
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Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
From what I have read, VAG have a prescribed method of flushing the system as there are 3 separate cooling systems. Never seen that info actually published.They use some magic unicorn flush solution that no-one else can have or access apparently. From what I've seen posted elsewhere, it can involve flush, fill, drive, flush, fill ,drive - and repeat. I guess that depends on what comes out when you flush it.

Just flushing your matrix cooling circuit won't flush the rest of the system. When I took my matrix out on Monday, I only got about 400ml of coolant out. It didn't empty the rest of the system, so I assume that could easily still have loads of crud in it.

I'm getting a new cambelt/pump/stat next week, so I'll ask to see the coolant that comes out.

I flushed my matrix on Monday and it's working better but I will fit a new one when it arrives. I also changed my expansion tank (takes 10 mins) for a newer non-silicant one. Just removes that issue as well.
 

Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
Not yet. Car still in garage and it's starting to drag on a bit.

First thing was to replace coolant temp sensor, as I couldn't do it. Turns out another bracket shares the same mounting bolt and that had to be removed, so it took my mechanic an hour to fit just that.

Mechanic then decided to do thermostat next, so if that solved the overheating issue, I could at least have the car back and do cambelt/pump later.

Getting to the thermostat proved difficult and he decided to attack the charge cooler and associated pipes (other on-line suggestions were to take alternator off). That was very hard work and he finally got it off. He had ordered a replacement thermostat and housing from TPS but they said it was a choice of 2 items and the only way to be sure would be to check the part number on the old unit. They did send the stock item they had (50/50 change right?) and it turns out I needed the other one. That is on 7 day backorder as there is such a demand for them (surprise, surprise).

So - currently waiting for new stat and housing. It might also take him a week to put it all back together. The engine design makes it almost impossible to replace consumable parts. Even the oil filter is an *rse to get to.

He did say that the stat housing had some debris in it that looked like sand and was consistent with previous reports about leftover sand in the block from the casting process. The actual coolant didn't look too bad, it had some limescale type debris in it but it seems that the stat housing and other pipework are collecting the sand and other debris. I've tried to link a photo of the sand in the stat housing.

https://ibb.co/FwXV8Vj

We'll try to flush it out best we can to see if we can get any more out. If you look at the VW technical docs, a proper full flush is a ball-ache, partly due to having 3 coolant circuits.

So - as and when the thermostat gets fitted, if that does not solve the problem I'll get the cam belt and pump changed. The pump is already there and has had the motorized ("shroud"?) part removed. This appears to be an upgrade, as there is paperwork to say that it can be fitted with or without. I've read up and seen a video showing that they can get gummed up and fail. Who knows!

I'll try to update when I'm a bit further forward.
 

jjp

Active Member
Nov 19, 2018
10
0
Birmingham
Has anybody tried using wynns radiator flush which is supposed to flush the coolant system, to help resolve blockages and loss of heat?.. My 64 reg 2.0 tdi fr st leon last week started blowing coolish air on the way home from work, although throughout the day when i was out on the road it was hot. I parked up and when i got in about 3 hours later had the check coolant sign, filled up and its been fine until yesterday when i noticed it wasn't blowing out as hot as usual, after the 3rd time driving today it was hotter then it had been but not as hott as it normally is... Mine has covered 91300 miles
 

Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
Has anybody tried using wynns radiator flush which is supposed to flush the coolant system, to help resolve blockages and loss of heat?.. My 64 reg 2.0 tdi fr st leon last week started blowing coolish air on the way home from work, although throughout the day when i was out on the road it was hot. I parked up and when i got in about 3 hours later had the check coolant sign, filled up and its been fine until yesterday when i noticed it wasn't blowing out as hot as usual, after the 3rd time driving today it was hotter then it had been but not as hott as it normally is... Mine has covered 91300 miles
Mine is a 14 plate 2.0 TDI FR ST with 98,000 miles and I'm afraid that a flush is only delaying the inevitable.

The heater matrix channels are so narrow that any sort of flush only partly cleans them out. It's a known design fault and really needs changing.

I took mine out and cleaned it with all sorts of cleaners, ran a hose through it and got some debris out but it is still only working at about 50%.
I still get less heat in the cabin but also the stupid post DPF regen coolant loss.

Seat will quote 8 hours labour+parts so about £1000+.

Using a guide on this forum and buying a matrix from a European supplier for c.£80, you can do it yourself in a couple of hours. When I checked 3 weeks ago, SEAT didn't have any in the UK as they were on backorder.

I'm assuming that if you used the radiator flush, you'd have to drain all 3 cooling systems and refill? That's a job in itself.

It's a ball-ache and it won't go away.
 

Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
Quick update on my car.

Still in the garage waiting for the new thermostat housing. On backorder with TPS and due on Monday (that's the last day of the 10 working day lead time). I now know which part I need but not one on-line retailer has them in stock (including Europe). Really hoping that TPS can deliver or I'll be really cheesed off. Even if that gets fitted, it may not solve the problem and then the water pump is next.

I also still have the new heater matrix in the boot that needs to be fitted.

Currently borrowing the wifes 2002 Volvo V40 1.6 petrol (no turbo). I can't complain but it's soooooo slow!

I want my car back.
 

Skilledmilk

Active Member
Feb 23, 2017
22
3
Has anybody tried using wynns radiator flush which is supposed to flush the coolant system, to help resolve blockages and loss of heat?.. My 64 reg 2.0 tdi fr st leon last week started blowing coolish air on the way home from work, although throughout the day when i was out on the road it was hot. I parked up and when i got in about 3 hours later had the check coolant sign, filled up and its been fine until yesterday when i noticed it wasn't blowing out as hot as usual, after the 3rd time driving today it was hotter then it had been but not as hott as it normally is... Mine has covered 91300 miles
As above, I'd recommend you replace the matrix as mine was really restricted when I replaced it. Same as you is noticed cool air, which did get hot during a regen but was also accompanied by losing coolant out the expansion tank.
I've done around 11,000 miles since replacement in August last year and the coolant level hasn't moved. You could try the flush but I think it may just delay the inevitable replacement. I remember when I looked up the part number from the matrix I was replacing that there were 'A' and 'B' revisions which may be VAG realising that there was an issue with the early implemented parts.

Sent from my ONEPLUS A3003 using Tapatalk
 

Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
As above, I'd recommend you replace the matrix as mine was really restricted when I replaced it. Same as you is noticed cool air, which did get hot during a regen but was also accompanied by losing coolant out the expansion tank.
I've done around 11,000 miles since replacement in August last year and the coolant level hasn't moved. You could try the flush but I think it may just delay the inevitable replacement. I remember when I looked up the part number from the matrix I was replacing that there were 'A' and 'B' revisions which may be VAG realising that there was an issue with the early implemented parts.

Sent from my ONEPLUS A3003 using Tapatalk
VAG did indeed launch a `revised` version and although they've never admitted it is an issue, all UK suppliers were out of stock of them!

Mine is a Valeo so I've bought the same. No idea of it's an A or B version (I have looked but can't tell). Apparently the Nissens one is quite popular as it has much wider channels.

https://www.buycarparts.co.uk/seat/leon-st-5f8/23695/10204/heat-exchanger-interior-heating
 

jf_cole

Active Member
Jan 28, 2020
24
7
Here is a question - does the coolant in the header tank circulate?

I ask, because could you in theory change your coolant over a few months? Remove the header tank coolant with a large syringe, refill with new G13. Then a month later do the same and keep doing this over and over?

I don't have any issues, but i want to prevent them.
 

Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
Have you got a Part Number? (are Cupra and 2.0 TDi's the same?)And do you suffer any possible air locks doing this?

Thanks!
The best thing you can do is enter your vehicle details to check:

https://www.buycarparts.co.uk/seat/leon-st-5f8/23695/10212/expansion-tank-engine-coolant

I've got the Topran one as it matched my engine code (CUPA). It also doesn't have the stupid silica gel satchet in it.

These are the OEM numbers:


No air locks as the only coolant you lose is from the expansion/header tank (I used a large syringe to remove the coolant). You just remove the hoses and connectors and swap them over. Re-attach everything and add some more coolant. You might need to squeeze the lower hose to make sure it's full of coolant but it's quite easy. Took me about 15 minutes.
 

Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
Here is a question - does the coolant in the header tank circulate?

I ask, because could you in theory change your coolant over a few months? Remove the header tank coolant with a large syringe, refill with new G13. Then a month later do the same and keep doing this over and over?

I don't have any issues, but i want to prevent them.
The coolant does recirculate when the thermostat is open. As the car has 3 coolant circuits, I'm not sure how effective your method would be.

You are also adding new coolant to old coolant and effectively diluting it with new coolant. You could argue that you'll never fully replace all of the old coolant. It also does not remove any gunk/debris, which is more of an issue for the heater matrix and water pump.

Easier option would be to drop off the lower radiator hose. That will remove a lot of the coolant (and gunk) but not all of it. Then top up with new coolant. That would probable replace 75% of the coolant in the engine (I'm guessing).

The coolant system is meant to be sealed and minimal maintanence. The coolant is meant to be good for 250,000 KM or something silly (hence the addition of the silica gel bags to make it last longer and subsequent issues).

Unelss you have any real problems, I wouldn't see a need to mess with it.
 

jjp

Active Member
Nov 19, 2018
10
0
Birmingham
So if I was to attempt replacing my matrix how would i go about draining all 3 circuits, or would a couple of drains with a hose flushing through the expansion tank do it.. Anybody got any links to a diy guide on the matrix
 

Brian Gordon-Stables

Active Member
Jan 16, 2020
223
75
Leicestershire, UK
So if I was to attempt replacing my matrix how would i go about draining all 3 circuits, or would a couple of drains with a hose flushing through the expansion tank do it.. Anybody got any links to a diy guide on the matrix
In a nutshell - you don't. The procedure to `properly` drain and flush/refill all 3 circuits needs vacuum tools and lots of £££'s spent (dealers say that only they can do it).

The workaround is to just access the matrix from inside the passenger footwell, remove it and clean it (ideally replace). You only lose about a coke can of coolant and can just top up the header tank when you're done. The system is supposed to self-bleed. Some people have tried to flush with a hose at the bulkhead connections but I can't get access to the clips on mine.

This does not drain the whole system or remove any other gunk in the rest of the coolant circuit(s). It is advised to at least dump the majority of the coolant (via bottom rad hose), possibly flush (some people top up with water, run it and drain again), then fill up with coolant. If you don't do that you increase the risk of the matrix getting clogged again.

I've found various guides etc that I've cobbled together into a Word doc. I'll try to post on here when I dig it out.
 
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