Coolant blown out from expansion bottle

Mark7

Member
Joined
Oct 16, 2022
Location
Antrim
TDI
2litre
I covered the footwell with towels and plastic sheets to catch any spillage, which was relatively minor and seemed to be only the contents of the connecting pipes that spilled out. I didn‘t do any special bleed or flush after, given the minimal loss of coolant. Kept an eye on the level in the expansion tank over the following days and topped up when needed.
It’s been fine since, with no drop in level over the 60k miles covered.
When you say you topped up did it go up and down for a few days had this done today the old matrix was blocked on driving the car since the heater is now like a heater again. I think a sign of a blocked matrix might also be more condensation in the car in the winter as the heater isn’t as effective mine was sort of Luke warm before the matrix was done
 

SkilledMilk

Member
Joined
Mar 31, 2018
Location
Glasgow
TDI
Leon MK3 (184) 2013
When you say you topped up did it go up and down for a few days had this done today the old matrix was blocked on driving the car since the heater is now like a heater again. I think a sign of a blocked matrix might also be more condensation in the car in the winter as the heater isn’t as effective mine was sort of Luke warm before the matrix was done
Aye it went up and down as the air that did get trapped moved around the system to the header. I also got much more heat from the ‘hi’ setting once the matrix was even too as sometimes the passenger side was cooler before the swap.
 

TedoGTD

New member
Joined
Dec 6, 2022
Location
Slovenia
TDI
2.0 tdi gtd
Hei guys,
my first mechanic wanted too changed headgasket, but then i read this forum and see that others have same problem, coolant blow out.
My car worked fine, no lossing coolant before, just one day starting blowing it from expansion tank but not every ride or day.

When temperature outside dropped i see that heating doesent work. I bought Nissens heater core and we did 3 time flush all the system before we changed it. Then we replace it with new one and put new thermostat.
Now its 3 months after and 2000km, car works perfectly and heating works like it was new.

Thank you guys

Cost 300eur with parts, headgasket replace is abouth 1500. Saved a lot of money and work.
 

8v-a3

New member
Joined
Dec 16, 2022
Location
Uk
TDI
1.6
Hi all,
Sorry for the long message but I found this forum really helpful and want to help anyone on this situation similar to mine.

My car started suffering with this problem 6 months ago when one day the warning appeared. No coolant at all in tank so I though it was definitely a leak, topped it up and the coolant stayed. I didn't know what to think but the mechanic checked for leaks and changed water pump. A couple hundred miles later coolant again gone. Mechanic advised to keep driving until the problem become more consistent.

Blowout kept happening, naturally I thought head gasket but no creamy residue on cap or other signs etc. Got it serviced as it was due and second mechanic checked for leaks - didn`t find anything. Blowout kept happening and saw some videos regarding egr cooler leaks.

I noticed that sometimes when I opened the coolant cap, some coolant would come back up into the tank. I thought maybe faulty cap so replaced that, but no luck. Took it to third mechanic who checked for leaks and suggested thermostat. At this point I researched and was sure that coolant was being burnt via egr cooler, mechanic suggested first change thermostat - again after some driving the blowout happened again. At this point I had lost hope and thought the egr cooler was linked to dpf cycle, that is when I found this forum.

Coming into the winter I noticed that I had luke warm air, condensation very quickly building up inside cabin, fan speed would reduce when turned heating to hot, but temp on dash was never above 90. I then noticed that after 250-350 miles the blowout would happen which I have read is about the dpf cycle. Looking at the success of changing heater matrix and my disappointment in my mechanics, I decided to change it myself. Ordered a nissens matrix and when I cut open my old one the coolant had become solid and blocked half of the matrix so I don't think it is worth trying to clean old matrix.

I can report after 500 miles that it has worked!! I am a newbie so took me six hours, relatively simple but hard to reach screws slow you down.

I was worried when a few days later the coolant level had dropped by about 100 ml but after filling up it has been fine since, must have been air locked in the system after matrix change.

Its interesting how this seems to be a common issue but not many mechnics I spoke to knew about this. Will keep you updated but this chat has helped me immensely.
 

anniebanani

New member
Joined
May 17, 2022
Location
Adelaide
TDI
2014 Golf Highline 110TDI
@anniebanani good news! 3 weeks today since heater core was bypassed and it has held the coolant in the exact same spot ever since. About 1500+km driving, freeway and local with absolutely no issues. It's been torture with no heat though - we're going through a bad bad cold snap here in Melbourne lol. Going in for fix on the 7th wooo!
Update: Back in November I had the heater core replaced and aside from a small drop in coolant straight afterwards - probably settling after the change - touch wood - everything has been fine. No loss of coolant, even after over 1000kms and several re-gens. Mechanic is scratching his head but it seems to have worked.
 

GolfSW98

Veteran Member
Joined
Feb 8, 2021
Location
USA
TDI
MK7 TDI
Regen last night- lost a few oz of coolant maybe. Coolant residue on pressure cap, can see it vented. Also, I previously mentioned I would be switching to G12evo coolant. Bad idea, VW literature says:
GEN III EA288 TDI (MY2015 2.0L TDI CVCA and CRUA) MUST continue to use G13 coolant.
 
Last edited:

tripLr

Member
Joined
May 9, 2021
Location
Wa. State, USA
TDI
2002 Golf
Hi all, decided to share my pain with VW community after ~8 months of troubleshooting by VW (Australia). 2013 Mk7 Golf 110TDI is pushing coolant out from the surge tank. Looks like gases enter the jacket under load, accumulate and then rush up to expansion bottled causing it to overflow - overflow pipe is tiny and most of coolant is blow out through the cap threads and sprays around under the bonnet. Done so far to no effect by VW: replaced water pump, multiple cooling circuit pressure tests, replaced expansion bottle, replaced cylinder head c/w gaskets etc., replaced EGR cooler, replaced intercooler, performed engine compression test, replaced some weeping rubber hose. Any idea is appreciated. Love the car but got quite frustrated by now. Few more points: never ever had overheating or gauge temperature moving beyond 90degC; following each "blow out" can clearly hear "hissing" noise coming from the heater core suggesting pockets of gas travelling through the system.
Head Gasket
 
Joined
Feb 23, 2023
Location
Scotland
TDI
20 ltr
Does anyone have a fix yet
I have A3 20tdi Quattro with the much the same issue. I can drive sensibly and it seems to be fine but if I drive car hard on full boost it will pore out about 2 ltr out coolant.
I’ve had water pump, expansion tank and cap, thermostat, radiator, heater matrix, head gasket then recon cylinder head and another new gasket.
I’ve heard there’s an electric water pump could this be the issue or the eve on the front of the engine.
Any thoughts on where to go next
 

GolfSW98

Veteran Member
Joined
Feb 8, 2021
Location
USA
TDI
MK7 TDI
Does anyone have a fix yet
I have A3 20tdi Quattro with the much the same issue. I can drive sensibly and it seems to be fine but if I drive car hard on full boost it will pore out about 2 ltr out coolant.
I’ve had water pump, expansion tank and cap, thermostat, radiator, heater matrix, head gasket then recon cylinder head and another new gasket.
I’ve heard there’s an electric water pump could this be the issue or the eve on the front of the engine.
Any thoughts on where to go next
What does your coolant temp via obd2 when the boiling occurs? There could be coolant valves not opening as well. You have coolant stuck in an area heating up and boiling over.
 
Joined
Feb 23, 2023
Location
Scotland
TDI
20 ltr
Not checked with diagnostics but car never overheats, you can leave car running all day and temp doesn’t go over 90.
You can drive car normal and it doesn’t loose any coolant but as soon as you start driving with the foot down it instantly starts pouring coolant out overflow on bottom of expansion tank.
I also checked cooling system for head gasket again with the little blue fluid tester that changes colour if gasses in system but never changed colour
 

iamhe

New member
Joined
Apr 25, 2023
Location
Aus
TDI
Mk-VII
This has been a great thread. Hoping it will save me from a four wheeled money pit. Mine is going into VW to get fixed, only b/c the repairs will be warranted.

My question for the thread is: Did this randomly show up for you? Or;
Did it start happening after your 140km water pump replacement? If so, how long after.

Wondering if some kind of scale gets dislodged during the water pump service that stuffs up the heating matrix. Or;
Is it something that one should be mindful of as it just backs up over time.
 
Joined
Feb 23, 2023
Location
Scotland
TDI
20 ltr
This has been a great thread. Hoping it will save me from a four wheeled money pit. Mine is going into VW to get fixed, only b/c the repairs will be warranted.

My question for the thread is: Did this randomly show up for you? Or;
Did it start happening after your 140km water pump replacement? If so, how long after.

Wondering if some kind of scale gets dislodged during the water pump service that stuffs up the heating matrix. Or;
Is it something that one should be mindful of as it just backs up over time.
 
Joined
Feb 23, 2023
Location
Scotland
TDI
20 ltr
Mine just started doing it one day, still haven’t got to the bottom of it. Thinking next step will be egr.
Let me know how you get on with yours at vw.
Fingers crossed they sort it out for you.
 

Zak2298

New member
Joined
Apr 26, 2023
Location
Italy
TDI
Golf 7 GTD CUNA
I found this thread online, I have golf 7 gtd with CUNA engine
I have the same problem
Replaced internal radiator
Problem persists
With odb temp max 101 this is a problem?
Possible Thermostat?

Next steps to figure out what the problem is?
 

Zak2298

New member
Joined
Apr 26, 2023
Location
Italy
TDI
Golf 7 GTD CUNA
@anniebanani good news! 3 weeks today since heater core was bypassed and it has held the coolant in the exact same spot ever since. About 1500+km driving, freeway and local with absolutely no issues. It's been torture with no heat though - we're going through a bad bad cold snap here in Melbourne lol. Going in for fix on the 7th wooo!
Would you explain how you bypassed heater core?
 

iamhe

New member
Joined
Apr 25, 2023
Location
Aus
TDI
Mk-VII
So good news!
Replacing the heating matrix appears to have fixed this.

I used to get a blowout every other day thanks to my commute. Several big drives later, the water level has only gone down ~5mm. There was quite a bit of gurgling behind the firewall for the first couple of days. Since then nothing.

Woot!
 

ipwright83

New member
Joined
Jul 18, 2023
Location
UK
TDI
Skoda Octavia
Hi there,

I've just been pointed to this thread. I've got a 2 litre diesel Skoda Octavia. I've got coolant levels dropping slowly (and looking a little murky - but I don't believe it's a head gasket issue) and also have no hot air (going to confirm later if it's just some fans blowing cold). Garage is unsure what it could be and is suggesting replacing parts methodically (fortunately they don't want to waste my money like a main dealer).

There's a lot of info in here, much of which I don't understand. I was wondering if anyone could advise on any sort of specific checks that can be done to try and confirm if my issue is the heater matrix?

I've read about an issue being regeneration related. Unfortunately I don't actually know how I can tell if my car is doing a regen or not: ( Also I've seen people mention a coolant overflow (is that an overflow valve, or when removing the cap when the engines hot)? Hoping someone could point this car n00bie in the right direction!

Thanks
 

Mark7

Member
Joined
Oct 16, 2022
Location
Antrim
TDI
2litre
Ok we have a 2013 golf same probs put a new bottle top on first no change then new water pump it was due anyway it helped abit then bingo back again. It’s the matrix as vw won’t admit liability the lines tubes are to small in it and get blocked up and it’s not always this silica bag a leaf debris can do it to. Skoda Leona Audi experience the same problems as it’s a design fault. You fit an aftermarket matrix Nissen or something it’s called it has wider channels and fixes the problem. Check if your heater feels warmer on one side when fully on ours was colder on one side and the heater had no real heat. After the fix the heater would now melt you, it was previously Luke warm and cold.
 

Mark7

Member
Joined
Oct 16, 2022
Location
Antrim
TDI
2litre
Ps get it bled correctly as you can destroy the water pumps doing it yourself as they need bled in order using a pc
 

Mark7

Member
Joined
Oct 16, 2022
Location
Antrim
TDI
2litre
Never open the coolant when warm as it will spill out and a lot of people overfill their bottles the bottle should really sit about min when cold as I said check your heater first after a good long run get out and feel the vents as you out the heat on
 

shocks

Active member
Joined
Jan 22, 2020
Location
Perth AU
TDI
Golf MK6 2.0TDI (103KW CFFB) Comfortline, Golf MK7 2.0TDI Highline (CRBC 110KW), Passat Alltrack Wolfsburg Ed. 2.0TDI (DFHA 140KW)
Check if your heater feels warmer on one side
In my Golf the vents can be different temperatures when A/C is in Auto, so I recommend just using the direct air function (button showing air coming towards you) and cranking up the heat. When my matrix was blocked there was a 10degC difference in air temperature between the two central vents and the outside vents. After replacing the matrix,the difference was less than 1degC difference.

. I was wondering if anyone could advise on any sort of specific checks that can be done to try and confirm if my issue is the heater matrix?
Other things to consider are odometer, most here have had the issue occur just over 100,000km.

Also, how much coolant are you loosing, matrix issue was usually enough to cause a low coolant warning every single time DPF regen occured.

Monitoring DPF cycle requires getting a cheap Bluetooth OBD2 dongle and using the VAG DPF app. Regens occur every 250 to 350kms from my experience .

if your loss of coolant is happening with the DPF regen cycles, there's a good chance it's the matrix.

With respect to working your way through potential causes, bare this in mind, the matrix will likely be the cheapest part to start that process with, so it's probably the low hanging fruit in this case.
 

ipwright83

New member
Joined
Jul 18, 2023
Location
UK
TDI
Skoda Octavia
That's a good question on the coolant. The vessel is so murky I can only see the level from above which is hard to measure. It does feel like it goes suddenly. I do actually have an OBD2 dongle that I've not really used so I can take a look for that app. We do a lot of running around town so I imagine the regen cycle doesn't kick in all that often. It's a 2013 car with only around 60k miles if I recall.

Useful to know that the matrix is the cheapest fix. I'll check out the things suggested and post back here.
 

shocks

Active member
Joined
Jan 22, 2020
Location
Perth AU
TDI
Golf MK6 2.0TDI (103KW CFFB) Comfortline, Golf MK7 2.0TDI Highline (CRBC 110KW), Passat Alltrack Wolfsburg Ed. 2.0TDI (DFHA 140KW)
The vessel is so murky I can only see the level from above which is hard to measure.
Well, usually if the coolant warning light comes on, you're about half way from the low coolant marker to the bottom of the bottle. If you look in you see the sensor, when the bottom of the two prongs are no longer in the coolant the light comes on. If you're at this point, you've already lost about 500ml of coolant.

I've never seen a coolant bottle where you can't tell the level, this is mine at 205000kms, also a 2013 tdi, the level is clearly visible as just on the Max line.

 

Elgars

New member
Joined
Jul 11, 2022
Location
Latvia
TDI
ASZ MK4 300+
Fixed mine. Turn out to be heater matrix blocked.
Replaced and no signs of coolant loss.
 

ipwright83

New member
Joined
Jul 18, 2023
Location
UK
TDI
Skoda Octavia
@shocks yeah unfortunately the bottom of mine is a bit brown stained so you can't see from the outside.

I've confirmed that I only have heat one side (driver side - right hand drive). But trying an ODB scanner it said "left temperature flap positioning motor - accuator jammed". So I'm wondering whether there may be multiple things going on and that the heater matrix might not be my issue 🤔
 

shocks

Active member
Joined
Jan 22, 2020
Location
Perth AU
TDI
Golf MK6 2.0TDI (103KW CFFB) Comfortline, Golf MK7 2.0TDI Highline (CRBC 110KW), Passat Alltrack Wolfsburg Ed. 2.0TDI (DFHA 140KW)
I've confirmed that I only have heat one side (driver side - right hand drive). But trying an ODB scanner it said "left temperature flap positioning motor - accuator jammed". So I'm wondering whether there may be multiple things going on and that the heater matrix might not be my issue 🤔
I had a actuator jammed warning for years too when I scanned and I don't think I ever noticed anything obviously wrong with the HVAC system because of it. If your current ODB scanner app provides the information, look for the kms since last DPF regen (or get the free VAG DPF app), if this is 0km or a very low number the next time you lose coolant, then this is a strong indication that the DPF Regen is initiating the event. This correlation has been linked to a blocked heater matrix so this is what you want to confirm before you spend a lot of money on diagnostics and repairs.
 

Rasamaha

New member
Joined
Jul 24, 2023
Location
Alusinamus
TDI
2.0
Hello,

I have similiar problem as most of you do with my Seat leon 2.0tdi 184hp cuna engine.

After a hard drive (2k+ rpm) the coolant just pours from coolant tank , if i drive under 1.8k rpm or just let it idle and reach working temperature the overflowing doesnt occur.
The C02 test didnt show any gasses in coolant tank. Temperature gage doesnt go above 90 degrees. Heating inside cabin works fine.
Changing the coolant tank lid didnt help, what could be the next steps for diagnosing the problem?
 

FJBGTD

Member
Joined
Jun 13, 2022
Location
Southampton
TDI
Golf GTD
Hello,

I have similiar problem as most of you do with my Seat leon 2.0tdi 184hp cuna engine.

After a hard drive (2k+ rpm) the coolant just pours from coolant tank , if i drive under 1.8k rpm or just let it idle and reach working temperature the overflowing doesnt occur.
The C02 test didnt show any gasses in coolant tank. Temperature gage doesnt go above 90 degrees. Heating inside cabin works fine.
Changing the coolant tank lid didnt help, what could be the next steps for diagnosing the problem?
It sounds like you may have a water pump problem, the water pump shroud is prone to sticking on the CUNA engine, also the plastic impeller is prone to spinning on the shaft. Remove the return line from the top of the coolant bottle to check for flow, the flow should start once the coolant reaches 65 degrees c, this is the temperature that the shroud moves into the open position.
 

hellbent987

New member
Joined
Aug 6, 2023
Location
Maribor
TDI
Golf 7 GTD
I cant believe i found this thread i thought im stupid for disagreeing with all mechanics that analyzed my car but i allways pointed to heater core and they never listen, so to tellmy story in short i own Golf 7 GTD 2015 CUNA and it has 294k km on clock and it had some ash buildup on DPF so i had it demounted cleaned and put back on, and my problems started after that, they had to drain cooling system and refill it and probably messed it up somehow, first i noticed my heater not working only left side warm and as you go to right colder and colder, and coolant started disappearing and i didnt understand where, i did hear gurgling behind dash sometimes then one day as im driving on highway i hear a burst and coolant blows into my face from vents and engine starts going over 90c so i pull over and see intake hose for heater core bursted out of the wall so i had to tow car to replace it, and my problems with no heat and coolant loss persisted then after some time my gf was driving to work and hot engine warning suddenly appeared engine temp went almost to red she had to pull over but coolant was at max on overflow tank, then i changed water pump and timing belt and did system flush but i noticed now another symptom, my coolant started to smell burnt and its colour is blacked a bit and i see also loss when dpf regenerates overflow tank spills, now i suspect maybe the overheating that happened might screw the gasket or maybe egr cooler so gases enter coolant and its black cos of that, all mechanics i went to say gasket and think im crazy for suggesting heater core...
 

hellbent987

New member
Joined
Aug 6, 2023
Location
Maribor
TDI
Golf 7 GTD
Also i wonder would it help temporarly to shut down engine just before its about to finish regeneration and then wait a bit for temps to lower, then restart, maybe that way overflow wouldnt happen?
 
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