VW Golf MK7 TDI - Heater blowing cold / Silicant bag in expansion tank


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By candellara - Monday, June 24, 2019 8:55:51 AM
I posted this on an old thread relating to the same issue but someone suggested i post a new thread

As stated, 6 months ago (during a motorway drive) we lost heat to the vents and we had gurgling noises from the dash. The car was subsequently booked into VW and their diagnosis was that there are no fault codes present but what is common on MK7 Golfs was that the silica bag in the water expansion tank ruptures and blocks the heater matrix. Price to rectify £819 for new matrix.

I didn't believe them and was a bit miffed that they hadn't tried to flush the system so i took the car away. I disconnected the hoses from the matrix at home and flushed with a hose and water was flowing freely. Upon reconnecting & top up, heat from the vents again!! The car only does local town driving and everything has been well for 6 months UNTIL, a recent motorway drive. Same symptoms, no heat from vents, gurgling noise and some water being forced from expansion tank on this occasion. Note that the coolant in the system is totally clean along with the expansion tank - no signs of any dirty contaminated water.

After returning home, i ordered a new expansion bottle & cap - very low cost and really to eradicate these items from being any cause. After fitting and topping up, we have heat again from the vents.

Well, today i opened up the old expansion tank with a saw - and, the silicant bag is not ruptured and is fully intact with all of it's crystals!!!!! Now this is becoming farcical as the amount of threads there are all over the forums about this exact problem and VW continuing to replace heater matrix's. One poor lady has had 3 heater matrix's as the VW dealer insists that the silicant granules have contaminated the system and continue to block the new heater matrix's. Indeed my local VW dealer wanted to relieve me of £819 for replacing the matrix - when we now know the matrix isn't blocked.

Any thoughts?
By Crasher - Monday, June 24, 2019 5:35:16 PM
The Golf 7 (MQB platform) heater matrix is extremely prone to getting blocked even when you are convinced it isn’t.
By laldog - Monday, June 24, 2019 6:20:47 PM
So if your matrix is fine and the dealer is wrong what is wrong with your vehicle??
By candellara - Tuesday, June 25, 2019 6:04:16 AM
laldog (24/06/2019)
So if your matrix is fine and the dealer is wrong what is wrong with your vehicle??


I don't know but i'm not convinced it's a heater matrix issue as all incidences of this seem to surround either the silicant bag rupturing or brown stained coolant from casting sand remaining in blocks.

Currently the vehicle has no issues - but it's only being used for short journeys. The problem only happens during longer motorway runs and becomes apparent when there is no heat to vents, gurgling sound from dash and water leaking from the expansion tank. Under the bonnet, coolant pipe to matrix is hot - outlet pipe is cold.

Short runs / city driving no problem. Heat from vents, both pipes to matrix piping hot, no water loss or gurgling noises etc. Temp gauge always reads 90o and no fault codes present when the system was scanned by VW
By Crasher - Tuesday, June 25, 2019 4:44:07 PM
Ignore the temp gauge, the readings are a joke. We have replaced a large number of MQB platform heater cores now and not once have I seen one of these tea bag things, plastic cylinder yes but nothing else. The system MUST be flushed absolutely clean.
By candellara - Wednesday, June 26, 2019 6:07:40 AM
Crasher (25/06/2019)
Ignore the temp gauge, the readings are a joke. We have replaced a large number of MQB platform heater cores now and not once have I seen one of these tea bag things, plastic cylinder yes but nothing else. The system MUST be flushed absolutely clean.


Still not convinced. If the matrix was blocked - it would be a permanent issue rather than an intermittent one? Why would it be that in normal city / town use the car has no issues - both pipes to matrix hot and heater working fine, no coolant loss etc and then you go on a high speed / motorway drive for 30 minutes - this issue suddenly appears?

Where VW don't have a coolant flush as part of the service schedule - is it coagulation of the G13 coolant causing issues?
By McTech - Wednesday, June 26, 2019 7:22:00 AM
Hi C,

It is possible that the issue is nothing to do with blockages in cooling system.

Could it be gas in the cooling system causing gurgling noise after 30 mins of the motorway.

e.g. egr cooler leaking under higher pressures, but yes we could expect increased temp at ECT

I don't know but maybe the heater matrix constricts when flow increases causing some cavitation

I'm not saying this is the case - but if your car was with me and the cooling system flows correctly I would be looking for other possiblities.

Then again Crasher has VAG tattooed on the inside of his eyelids - a vast amount of experience.

Just thinking aloud....

M
By Trovs - Wednesday, June 26, 2019 3:29:58 PM
Water pump?
By candellara - Thursday, June 27, 2019 5:04:42 AM
McTech (26/06/2019)
Hi C,

It is possible that the issue is nothing to do with blockages in cooling system.

Could it be gas in the cooling system causing gurgling noise after 30 mins of the motorway.

e.g. egr cooler leaking under higher pressures, but yes we could expect increased temp at ECT

I don't know but maybe the heater matrix constricts when flow increases causing some cavitation

I'm not saying this is the case - but if your car was with me and the cooling system flows correctly I would be looking for other possiblities.

Then again Crasher has VAG tattooed on the inside of his eyelids - a vast amount of experience.

Just thinking aloud....

M


It's a tough one and alot of head scratching but one thing's for sure - i don't want VW to start swapping out parts without a firm diagnosis - that's one of the reasons we pay VW £150 per hour rather than an independent garage. There are so many incidences of this across the web and some people report that even after a new heater matrix at a cost of over £800, the fault still exists. There must be a definitive answer to this issue where someone has a identified the problem and made a correct diagnosis
By McTech - Thursday, June 27, 2019 5:00:37 PM
Tests can be done to check for cavitation using a WPS on a scope.

EGR cooler can be tested pressure test fairly easily.

A quick gas test on cooling system.

Tests really need to be done when fault (going cold) occurs.

I would do all @ £50 and hour....BigGrin

£150 ph buys you "similar" but with a leather sofa to sit on - filter coffee and a copy of Hare and Hounds...

and you'll still get a new matrix

M
By Iver - Friday, June 28, 2019 5:32:23 AM
A flow meter on the pipe in to the matrix and temp sensors either side of the matrix captured on a scope would paint a pretty picture should you want to go that far an prove the point. Add some clear pipework to look for air bubbles.

Might be worth looking on Erwin or Rosstech for a TSB. IIRC one does exist.
By Crasher - Tuesday, July 02, 2019 11:00:26 AM
Found one, well two actually (in one TTS mk2 expansion tank ?) and I have seen one before. It is VAG part number 4E0 121 176 and retails at £10.99, described as “Silicate cartridge for expansion tank” and is meant to beef up the Silicate levels in modern antifreeze, apparently...

By candellara - Friday, July 05, 2019 10:48:28 AM
Well we've covered about 400 miles since the car's last "motorway" episode

No loss of water, no heating problems - car is running fine.

Again, because of this - i still dispute VW's diagnosis of the heater matrix. Glad i didn't part with over £800.

I'll keep the thread updated as and when (and if) we get further trouble. Worth noting that after the car's last issue - i did change both the expansion tank and cap as they were so low cost it was worth fitting new parts just in order to rule them out
By Thema - Friday, July 05, 2019 12:01:30 PM
Generally I would call 400 miles without fault a cure! So I really hope that's it.
But, to go back to these bags in the expansion bottle, I've never actually come across one but they certainly seem to be more trouble than they're worth. And I'm having trouble seeing them as worth anything!

Peter
By Blackdog - Friday, July 05, 2019 4:42:08 PM
The only test for these is a 30 mile run high gear low rpm. They won't heat at low speeds or high rpm.
By Crasher - Friday, July 05, 2019 6:34:26 PM
One odd thing we have found on the MQB heating system is dash vent temps much colder on the right than the left so if the owner lets us go that deep, we lag the ducting (moulded into the dash) with Dyna Mat and this significantly raises the temperature of the right face vent.
By McTech - Saturday, July 06, 2019 6:02:49 AM
I got a little insider info yesterday.

Apparently the first batch of heater matrix (not sure on the plural for matrix) cores!

These had sand left inside them from poor QC after manufacture.


There part number is superseded now.


Also could be a issue with electronic control on water pump...

Anyway a little titbit..

Mt
By andymac - Saturday, July 06, 2019 6:22:18 AM
Just had a look because I didn't know and I'm a bit of a pedant for these things. Matrices is the correct plural term.

andymac



By Crasher - Saturday, July 06, 2019 6:52:28 AM
What about Lexus, Lexussusses, Lexi, Lexie? Anyway if the heater pump (when fitted) cavitates (third person singular simple present) it is often due to a failed intercooler pump and comes up as an engine fault code.
By candellara - Monday, July 15, 2019 11:54:28 AM
candellara (05/07/2019)
Well we've covered about 400 miles since the car's last "motorway" episode

No loss of water, no heating problems - car is running fine.

Again, because of this - i still dispute VW's diagnosis of the heater matrix. Glad i didn't part with over £800.

I'll keep the thread updated as and when (and if) we get further trouble. Worth noting that after the car's last issue - i did change both the expansion tank and cap as they were so low cost it was worth fitting new parts just in order to rule them out


Well - after a couple of weeks with no issue. went for a long run (25 motorway miles) and then on idle, heard a gurgling noise from behind the dash (only for a couple of seconds). Checked to see if there was any hot air blowing from the vents - but it was difficult to tell as it was so hot anyway - but i don't think so. Temp gauge all ok, no loss of coolant etc

So car still has any issue of sorts - but it only intermittently happens after long runs and then will return to normal. I might try flushing the matrix this weekend but on another forum there was a post from a guy with a 2013 A3 - same issue and it was as Crasher had said - matrix, but it only happened when the car was going though its dpf regeneration phase
By Crasher - Monday, July 15, 2019 2:11:54 PM
It is pointless flushing the matrix, I have cut one open and the capillaries are so thin it is impossible even with a pressure wash.
By Iver - Wednesday, July 17, 2019 4:11:57 AM
Is there some sort of Acid that would clean it through ?
By Crasher - Thursday, July 18, 2019 5:11:28 PM
At the expense of the entire cooling system to prevent the replacement of a reasonably accessible part?
By McTech - Thursday, July 18, 2019 5:45:44 PM
Iver (7/17/2019)
Is there some sort of Acid that would clean it through ?


Lysergic?...Hehe
By Thema - Friday, July 19, 2019 2:43:36 PM
McTech (7/18/2019)
Iver (7/17/2019)
Is there some sort of Acid that would clean it through ?


Lysergic?...Hehe


Might give you other things to worry about, like the dragons in the kitchen?


Peter
By McTech - Friday, July 19, 2019 3:23:12 PM
Thema (19/07/2019)
McTech (7/18/2019)
Iver (7/17/2019)
Is there some sort of Acid that would clean it through ?


Lysergic?...Hehe


Might give you other things to worry about, like the dragons in the kitchen?


Peter


lol -
oooooor so000ooft spanners....!!!!!!!!!!
By Iver - Saturday, July 20, 2019 11:48:06 AM
Crasher (18/07/2019)
At the expense of the entire cooling system to prevent the replacement of a reasonably accessible part?


Good Point !!!
By candellara - Friday, August 16, 2019 3:23:40 AM
As an append to this, the reason i'm unconvinced the matrix is blocked is that after a simple flush - the heating system works exactly as VW intended. If the matrix was blocked - this wouldn't be the case.

My latest thoughts are that some component is causing air to be ingested into the cooling system - thus causing the heater matrix to airlock (no heat from vents) and the pressurising of the system (water being expunged from coolant bottle after long runs). This seems to only happen after long runs or after a hundred or so miles. When i "flush" the matrix - it expels all of the air, causing the system to work correctly until the next "cycle" when air is ingested into the cooling system

After some reading - EGR cooler? or EGR valve must be suspect. Is this possible?
By McTech - Friday, August 16, 2019 7:48:35 AM
candellara (8/16/2019)
As an append to this, the reason i'm unconvinced the matrix is blocked is that after a simple flush - the heating system works exactly as VW intended. If the matrix was blocked - this wouldn't be the case.

My latest thoughts are that some component is causing air to be ingested into the cooling system - thus causing the heater matrix to airlock (no heat from vents) and the pressurising of the system (water being expunged from coolant bottle after long runs). This seems to only happen after long runs or after a hundred or so miles. When i "flush" the matrix - it expels all of the air, causing the system to work correctly until the next "cycle" when air is ingested into the cooling system

After some reading - EGR cooler? or EGR valve must be suspect. Is this possible?


See my first two posts on page 1????
By Iver - Friday, August 16, 2019 4:30:32 PM
After some reading - EGR cooler? or EGR valve must be suspect. Is this possible?


By pass it. Easy. Prove the point

Or as McTech, measure it properly with WPS and Pico. About £3k in tools alone
By Blackdog - Friday, August 16, 2019 6:16:06 PM
When you do a simple flush of the matrix the car works right but yet your matrix can't be blocked?
Take it from me and crasher without looking at the car were fairly certain it is.
A simpler test without spending a fortune would be to remove the matrix drain it and weigh it.