How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Nathan B Your Own Question
Nathan B
Nathan B, NVQ3 motor mechanic
Category: Volkswagen
Satisfied Customers: 151
Experience:  Over 20 years experience including running my own garage working on a wide range of vehicles.
Type Your Volkswagen Question Here...
Nathan B is online now

I have a 2013 7 diesel golf 2.0 litre GT and have owned

This answer was rated:

I have a 2013 mark 7 diesel golf 2.0 litre GT and have owned since new. It is 3 months beyond its warranty and has 59,000 miles, mostly motorway. Always main dealer serviced and well looked after.
3 weeks ago the heater started to blow ambient temp air only. The next day on turning the ignition, a red warning light illuminated saying "check coolant level". I did not start the car but called the AA. The coolant was just below the sensor level so they topped it up with about 1/2 litre of antifreeze and started the engine. The heater blew only cold air and the mechanic was concerned about the heater manifold. He saw no leaks. The engine operated at normal temp 90 degrees. The main dealer said the water pump was leaking and change deniers it together with the cam belt. They said that the leak was minor because the silicone bag inside the pump remained intact. They returned the car saying that the heater still did not work because there was an air lock in the system and I should expect the coolant level to fall and to top it up. A week later I returned the vehicle because the heater was still not working. The engine never reached a temp of more than its normal 90 degrees and the coolant level never dropped below the minimum line.
They have now diagnosed a leak in the inlet manifold and say that the engine overheated which caused the original water pump impeller to seize and the silicone bag in the original water pump to break (a change to the original facts given) and the released silicone has a fatally damaged the heater matrix.
Please can you tell me:
1) What volume of coolant must be lost to trigger breakage of the water pump silicone bag?
2) Would the silicone bag break and water pump impeller seize with the engine still running perfectly normally and at normal temperature?
3) If silicone was released from the water pump, would this fatally damage the heater matrix?
4) When changing this water pump, would an "expansion tank" be fitted at the same time routinely or would this tank only be replaced if the silicone bag in the pump had broken?
Many thanks
I'm Shantal and I'm a moderator for this topic.
I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Pro
you had already found your answer or if you still need assistance from one of the Professionals.
Please let me know if you wish to continue waiting or if you would like for us to close your question?
Thank you,
Customer: replied 2 years ago.
please help me if you can?Best wishes,John

Hi there.

Welcome to my name is ***** ***** I hope I can be of help to you today. I strive for customer satisfaction with the service I provide on this site so I well be as helpful as I can and as in-depth with the answer as possible.

Firstly though, I don't know what your technical knowledge of cars is but I have never heard of a silicone bag in a water pump ever. They have a small pressure relief bung that will fail and coolant will leak from it just behind the pump outer pulley. if this was leaking you would see a significant amount of fluid loss and also when the pump was removed you would see the remnants of coolant on the outside of the pump.

In answer to your questions then.

1. A half litre of coolant loss wouldn't usually be enough to cause a problem but with the loss of heat in the car would lead me to believe that the coolant level loss is a lot more and the internal matrix could be blocked or airlocked.

2. If the level s very low then the pump would run dry and the lubricant in the bearing would wear out because the pump is supposed to be run wet and this would cause the shaft to overheat and possibly cause the impeller to work free from the shaft as it is only pressed on and is plastic causing it to stop rotating and this would cause the car to overheat. So yes the impeller can seize while the car is running and the impeller can just work loose on its own as well due to wear and tear but usually after more mileage than you have done but never say never.

3. if foreign bodies did get into the coolant system this could cause the heater matrix to block as the channels are quite small but it would take a lot to block the whole matrix up.

4. when changing a water pump and timing belt it is not common to fit an expansion bottle. in fact I have only done this myself if there had been a major overheating problem and oil has got into the coolant system and I couldn't get the oil out if the bottle.

But really John, I would never give a car back to a customer with the heating not working properly as this means there is still a problem. This wad the original problem you had with the car and the fact they first said that the (never heard of) silicone bag was still in tact the first time they worked in the car and then the second time it had miraculously broken I wouldn't be trusting what I am told from them. Main dealer or not.

A full investigation into the heater matrix needs to be done really by removing it and checking it for blockage and then fixing it. and once the coolant system is refilled a pressure test will need to be carried out to make sure no other damage or leaks are present.

I hope this has helped you with your problem. If you require any further help on this matter you can still post on this thread even after you have accepted my answer as this doesn't close out the question. Also, if you need help in the future you can contact me via my profile on this site and I will be happy to help you again.

Please remember to rate my answer as this is how I get paid and any feedback is very much appreciated.

Thank you in advance.


Nathan B, NVQ3 motor mechanic
Category: Volkswagen
Satisfied Customers: 151
Experience: Over 20 years experience including running my own garage working on a wide range of vehicles.
Nathan B and other Volkswagen Specialists are ready to help you
Customer: replied 2 years ago.
Dear Nathan,Thanks for your reply which is very helpful and I have given you top marks and a tip already. There is mmuch more to the story. I just typed for half an hour but when I rated you I think I lost everything so I'll start again in a few minutes. The story is fascinating !
Customer: replied 2 years ago.
Dear Nathan,Thanks very much for your reply which was excellent. Things have moved on a bit and I have the Golf back at home. It's still not right after £2000 of main dealer repairs and their explanations just don't make sense. As a young man I spent time as a mechanical engineering apprentice and passed the national exams. I had my mark 1 escort in bits more often than I had hot dinners and would think nothing of removing the cylinder head, updating valve springs etc. I am not a trained auto mechanic.The story of my Golf over the last 3 weeks is fascinating and I have been given lots of conflicting information by the main dealer. Luckily, I wrote down everything they said at the time and it's now clear how the story has been changed.When I collected the car from the main dealer yesterday, just before closing. I was able to question the service department manager and examine the old parts and take photos of them. By the time I had driven home (about 20 miles) the heater was again blowing cold and the coolant level had dropped to below the minimum level. The original problems had returned.As you know, I purchased this 2.0 diesel GT golf from new and it is just outside of its warranty, having been main dealer serviced from new. It has 59,000 mainly motorway miles. It has been trouble free until 3 weeks ago when the heater started to blow cold air whilst driving. Everything else was normal and so we continued our journey about another 30 miles and parked. The next day I turned the ignition on and the red "check coolant level light" illuminated. I did not start the engine but called the AA. The Patrolman topped up the coolant level with about 500ml of antifreeze and ran the engine for over 30 mins. He said that the engine sounded "sweet as a nut" but we definitely had a problem because the heater would only blow cool air. The engine temperature never went above its normal operating temperature of 90 degrees. The Patrolman could find no evidence of a leak and said that we could drive home but to watch the engine temperature gauge and to stop and call the AA if the temp went above 130 degrees. We drove home 150 miles and the car behaved normally except for the heater blowing cold air. The temp gauge stayed exactly at 90 degrees as normal.The next day I checked the coolant level which was almost unchanged (dropped very slightly) and I took the car to the main dealer about 20 miles away.I was told by the main dealer that the water pump had been leaking and they replaced the water pump and cam belt. They said that the silicone bag (which I now know is in the plastic coolant expansion tank on the top left of the engine bay, where you normally top up coolant) had not released its contents and so the coolant leak from the water pump had been minor. They had trouble getting the heater to blow hot air and told me that this was due to trouble bleeding the system because of an airlock and the engine just needed to run for longer to resolve this. They told me to top up the coolant level over the first few days as the air lock became displaced and there was a sticker on the steering wheel to remind me to do this. When I collected the car the heater was still blowing cold air.Over the next week I topped up the falling coolant level twice. It never fell below the minimum mark on the coolant expansion top up tank. The engine temp never went above its usual 90 degrees. However, the heater still blew cold air.I returned the vehicle to the main dealer. They kept the car for another 5 days and replaced the heater matrix and also the inlet manifold (with intercooler). I asked questions and took photos of the old parts (allegedly removed from my car) and they actually gave me the coolant expansion bottle to take home.The service department managers explanation of events was as follows:I was told that the problems all started with a water pump issue. They pointed to a metal sleeve on the outside of the water pump which can slide backward and forward to cover and expose the plastic impeller. They say that this metal sleeve got stuck in its extended position and occluded the impeller and therefore coolant could not circulate. As a result of this, the coolant boiled off from the expansion tank and the coolant level dropped. I was also now told that the water pump had never leaked. I examined the water pump myself, which they said was the old one from my car and I compared it to a new one straight out of the wrapper. The metal sleeve on both pumps moved freely, but on the new pump there was less resistance and movement was smoother. Otherwise both pumps appeared to be identical.I asked how if the impeller was not circulating coolant and if coolant had boiled off, why the engine temperature gauge had never gone higher than 90 degrees. I was told that the gauge is not very sensitive and coolant pressure can build up resulting in loss of coolant volume without any change in temperature as shown by the gauge.I was now
Customer: replied 2 years ago.
I was now being told that the coolant loss was sufficient to cause the silicone bag inside the expansion tank to release its contents and this contaminated the cooling system and blocked the heater matrix, causing the heater to fail. This is a change to the original story (which I cannot verify because the member of staff whom I initially dealt with has now left the company). They now also said that at the time of changing the water pump they had to flush the cooling system 4 times to remove the contaminant. This was the reason for fitting a new expansion tank. Originally I was told that they did not know for sure whether the heater matrix had been damaged or not, yet they recommended they change the heater matrix as well, just to make sure they fix the problem.This was the first time I had heard this story and it is very different from the facts initially given to me when I collected the car after its first visit, when I was told that the problem was a leaking water pump which would need to be replaced and also that it would be normal practice to change the cambelt at the same time. I was originally told that the water pump leak was minor because "there is a silicone bag inside the system which is still intact which was good news". Also, I was originally told that they did not know for sure whether the heater matrix had been damaged or not, yet they recommended they change the heater matrix as well, just to make sure they fixed the problem.I examined the old expansion tank which allegedly came from my car. Inside the plastic tank, on the right side of the tank (this would be the side of the tank nearest the engine when looking from the front of the car) is a bag made of white dense plastic mesh measuring about 4 x 6 cm and this is the bag the dealer refers to as the "silicone bag". I felt the bag with my fingers and it appeared to be intact and firm, still with its contents inside (granules or possible a gel substance). Also, the lower half of this plastic tank is stained with a brownish substance and still has reddish brown granules inside floating in water residue. There is a clear mark around the tank suggesting that whatever caused the staining had been in contact with the plastic for some time. The service department manager said that because the silicone bag actually looked to be intact and because its contents were still apparently within the bag, he did not know where the brown "contaminant" had come from.I do not believe that this expansion tank came from my car because:Both the AA Patrolman and myself would have seen the brown contaminant and the dark stain on the plastic tank. I watched the Patrolman remove the cap and add coolant to the expansion chamber and I remember thinking how clean and pink the coolant inside was. The expansion chamber looked like new. The dark brown staining on the chamber I was now being shown would have been obvious on sight.
2) Surely, if the system had been flushed x4 there would not still be brown bits floating in water residue within the tank, unless they fitted the new expansion tank before flushing out the contaminant.
3) The silicone bag in the old plastic coolant expansion tank appears to be intact with its contents still inside. This suggests that the reddish brown contaminant in this particular tank came from somewhere else. The service manager initially said that he did not know where the brown contaminant in the tank had come from but then changed his mind and insisted it was from the contents of the (silicone) bag.When I returned the car to the main dealer after the water pump replacement and told them that the original problem was still present and that the heater was still blowing cold and the coolant level appeared to still be dropping, the dealer performed a pressure test on the cooling system and found the system to be losing pressure. This they claim was due to a coincidental coolant leak from the inlet manifold. They say that on removing the inlet manifold, there was evidence on the valves of a coolant leak from 2 ports probably coming from the intercooler.They said that all this was extremely bad luck and that two systems (cooling and inlet manifold) had failed simultaneously. I do not find their explanation plausible and I do not believe that the contaminated expansion tank I had been shown actually came from my car.Does the dealers story sound plausible to you?What do you think happened to my car?What would you do now if you were me?I can send you photos of the old parts if it helps?Best wishes,John

Hi John.

First of all, thank you for replying and taking the time to type the life story of the problem for me. If you can send on the pics for me to view that would be brilliant but I will give you advice anyway and once i look at the pics i can give you more.

My god. Where do I start really. There is a lot of conflicting information there.

Firstly. Why didn't they do a pessure test the first time when they said that the water pump was leaking and if they did do one to find the leak that they said was coming from the water pump, why didn't they do one afterwards to check that the system was in fact good again. If they had of then they would've noticed the leak from the manifold at the time. In saying that though, maybe the manifold wasn't leaking the first time and beacause of pressure build up it then caused the leak in the manifold but it is difficult to say now after the fact.

On the issue of the expansion bottle and the brown staining, i would say that you would've seen the hard stain on the bottle yourself if it was there when you were topping up the level yourself and also they would've noticed it also if it is from the bag as the service manager is now saying ( although he said at first that it wasn't). In my experience a reddish brown residue in the coolant system would either be from rust entering into the system or more likely radweld or the likes that will stain everything but rust will occur when you run the system without antifreeze in it by having a major leak that you just keep on topping up with water. So in summary, i don't believe that that is your expansion bottle. I wonder though, most plastic items in cars have a stamp into the actual moulding that has the date that the part was made and you could compare this to another plastic part on the car and see if the dates are close by ( within a month or 2 really) if they are very different then it would seem to me that it is from a different car. The stamp would look like a circle with an arrow on it pointing to a number from 1-12 and either another one next to it with a yr or the yr is stamped into the middle of the first circle.

It is difficult to say what has happened, but i feel you have been mislead by the dealers. I would've done things a lot differently as i don't like fitting parts in the hope of fixing a problem i like to do as much as i can to prove that i have the problem so it is fixed the first time. I'm not saying i'm perfect though, i have got it wrong in the past and i would always hold up my hands and say it. I always believed that if i was honest with my customers and told them everything as i was doing it that even if i got it wrong then they would return as customers because there are a lot of cowboys out there. And also if i did get it wrong i wouldn't charge customers full price for parts that i had fitted if they couldn't be removed or even at all sometimes if i have gotten it really wrong.

Anyway, back on subject.

Before i go on though there is one thing i want to say and that is that if there is pressure build up in the system then the temp will rise. Even if only a bit, but it will rise. Especially if as they say that the impeller isn't circulating the coolant then as the pressure builds up the temp will rise more than normal. You would notice this more when the car is stationary rather than driving as when drivingthe cold air coming through the front of the car will keep the temp down a bit. But still you would notice a difference in the guage. The guage is given its reading from the sensor on the engine block so it is fairly sensitive otherwise why have it there.

I'm sorry if i am flitting about a bit but i am trying to answer every part of your post if i can.

Back on to what i think happened to your car then. I don't think the initial problem was with your water pump and possibly was with your manifold leaking slightly, but as i have said, this is hard to say after the fact. I do think that somehow, air is getting into the heater matrix and airlocking it though. if, as you have said that they have replaced the matrix then the new one should be clear of any debrix and should be able to be cleared of airlocks. If there is a stubborn airlock then you can backfill the system to erradicate this manually and then if the airlock reappears then there is air getting back in to the system from somewhere like a jubilee clip or a connection somewhere. Another pressure test will locate this though.

It is a strange problem though. I do wish the car was in front of me so i could go through things with you step by step and then we could have that eureka moment together.

I am racking my brains thinking of scenarios that would cause your problem and the only thing i keep coming up with is air getting into the system somewhere near to the matrix to let air into the system and airlock the matrix. Under a pressure test though this should show up as a leak. Once the leak is found and tightened then you could backfill the matrix and the rest of the system and the problem should be fixed. The only other way that pressure could be getting into the system if there isn't a leak is through the head as a crack, but this would only usually occur if the engine had overheated badly but can be a manufacturing fault sometimes. But this is very rare.

If i was you i'm afraid i would not go back to the dealer again. I know you have spent a lot of money with them already, but none dealers can sometimes be better than dealerships ( I'm saying this even though i did my apprenticeship at a main dealer where i learnt to be as honest as i can be, which can be my downfall). They should start at the beginning and think of it as a new fault ( if any of the parts that the dealer fitted have to be replaced due to being faulty then they are covered by warranty so don't stress about that). A pressure test needs to be done to elliminate any leaks in the system then go from there to find the cause of air getting into the system or pressure building up and causing the fluid to escape and so causing the air to get into the system.

Again John, I hope i have helped you in this matter. If you have any more questions on this or you just want me to clarify anything please don't hesitate to post back so i can help you more. Unfortunately, i'm in ireland living nowadays so i am not able to drive to you to look at the car myself ( which i would do if i could just to help you more). I will answer any questions you have and give you as much advice as possible on this matter.

Again, if you need help in the future please contact me via my profile and i will be happy to help you again

One last thing but i should've said this at the beginning, thank you for accepting my answer and for the bonus. It is very much appreciated, but my only goal is your happiness with the service i provide you on this site.

Thank you again.


Customer: replied 2 years ago.
Dear Nathan,Thanks so much for your reply and advice which is really helpful. I have attached two photos of the expansion tank which they gave to me and said was from my car. Could the brown stain and the particles in the tank be oil? What is the role of the substance in the "silicone" bag in the expansion tank and what causes this to be released and could it block the heater matrix?I have topped up the coolant level again and taken the car for a*****and the heater has started to work again, but only partially. There are 4 heater vents on the dashboard, one facing the passenger, two in the middle of the dash and one facing the driver. Well, the passenger vent blows hot air, the middle two blow warm air and the driver vent blows room temperature air. All vents are in the open position and fan maximum and heater on full. The air direction knob is rotated so that heat blows onto the driver and passenger.Is there a valve which shuts off supply of heat to the heater when the coolant level falls below minimum which could open again when the coolant level is topped up again ?Best wishes,John

Hi John.

Ok, i've done a bit of research for you in connection with the silicone bag in the tank. The bag contains silica gel and is for corrosion protection within the system. New coolant fluids contain an amount of silicone in them and the idea of the silica in the bag is to maintain a level of silica in the fluid. It is not there to break in connection with overheating of the system, but in saying that, they have been known to break open and cause blockage to heater matrix's. The replacement of the matrix though should have cured this problem and the fact that the bag hadn't broken the first time they worked on your car then i don't think this was the cause of the initial fault. That is unless it was missed the first time and it had in fact broken open and caused the matrix to block and in fact was not a problem with your water pump at all because if there was a blockage in the matrix this would in fact cause pressure to build up in the system.

The heater blower system isn't that complex really. It consists of a radiator (Matrix) Which when the blower is set to the hot position it blows across the matrix and down the ducting and into the vents and into the car. When the blower is set to cold, a flap covers the matrix in the heater system and cool air is then blown down the ducting to the vents etc. With the duel systems where you can have different temps on each side of the car there are flaps within the system that car direct different variations of cool and hot air into the vents and maybe with all the work that has been done on the heater system that one of these flaps isn't in the correct positioning and so this is why you are getting different temps across the car when it should be hot so maybe you could try and test the heating system with different temperatures on both sides of the car and see if anything changes at all. There isn't a valve that turns off hot air when the level drops at all no. Now, I haven't stripped down many duel heating systems but i don't think that there is 2 flaps over the matrix - 1 for the passenger and 1 for the driver - But if there is then it could be that there was still some debrix left in the system even though it was flushed 4 times apparently and this may have blocked part of the matrix again. But as i have said, this is only an assumption on my part but i will do a bit of research for you if you want.

I am just going to look at the pics and i will post my opinion to you then just in case when i look at the pics i lose what i have just typed.

I'll post soon.


Hi again john.

I've just looked at them there. Is the debrix a kind of sandy feeling to it? Or gritty? It doesn't look like an oil deposit because that usually is just blacky really unless it has been mixing for a while and then it is like a creamy kind of texture and lumpy. But it looks kind of gritty to me from the pic. I think if what you said in the life story post, that you noticed that the coolant looked very pink when you were looking at it with the AA patrolman then you would've noticed the staining rather than the pink colour in the bottle and the patrolman would have said to you that there is contaminent in the system.

I am going to send you back one of your pics with a circle on it because i want you to check it to see if that is the date stamp of manufacturing so you can let me know what it is.

Hi john.

Here is the pic i want you to look at.



I hope my advice is being helpful to you John.

Thank you again.


Customer: replied 2 years ago.
Dear Nathan,Thanks again for your help which is fantastic. I really want to know what has happened to my car!pThe contaminant inside the expansion tank is oily and gritty, like very fine sand. Also, it has stained the inlet and outlet pipes on the plastic tank. Both the AA guy and myself would have seen this contaminant as the tank looks awful from the outside. But why did they change this tank at the same time as the water pump - its possible they didn't change it but just wrote that they had changed the tank on the invoice to cover themselves in case of problems (this is called "safetynetting" and lots of Professions do it - of course you are not supposed to tell outright lies to cover yourself in case you made a mistake, but people do). It's also possible that this is my tank and this contaminant was a result of something they did at the garage when changing the water pump, hence them having problems getting the heater to work and having to flush the system. Please note that when I collected the car the first time there was no mention of any of this. They told me that they had changed the water pump which was leaking and that the heater was not working because of an air lock. They were having trouble bleeding the system. At handover they said that there was still an air lock and the engine just needed to run for longer and I would need to top up the coolant when the air lock cleared. I wrote everything down during the conversations and I wish I had recorded it all!Concerning the date on the tank, there is a circle stamped into the plastic in the place you have circled on the photo. I can see that there are marks around the outside of the circle like a clock face but other than that, nothing else stands out even with a strong magnifying glass.Concerning the heater, it's not dual climate and I am sorry for not making that clear. The driver side vent still blows cool, the middle vents are warm and the passenger side vent is hot.So what is in the tank that is oily and gritty and how has it got there?Best wishes,John
Customer: replied 2 years ago.
Nathan I forgot to say that the old expansion tank is stamped order the rim on the left side with the numbers 131461 12Does this help?Best wishes,John

Hi John .

The only reason I was asking to look at the date was to try and see if it was your bottle or not but it doesn't matter really. The debris looks kind of rusty to me almost like radweld. So I'm still doubtful that it is your bottle.

It seems to me that your matrix is still blocked on one side and that is why you are getting hot air on one side. The best way to clear this would be to back flush the matrix from the outtake pipe with the intake pipe disconnected and using a hose with a good pressure cleat out the matrix and then refit pipes bleed the system and recheck it again.

With the blower switched off but the engine running does the air get slightly warmer on the drivers side at all?

I think though that the silica bag that the dealer is on about had broken thE first time and blocked up the matrix. which caused the initial problem. back flushing thE matrix may have fixed it the first time without replacing but replacing is the best option but I don't think they back flushed the system and some debris got back in to the new matrix.

My advice now would be to get the matrix back flushed (try and catch the first bit of fluid with a jug if possible to see the grit in it) and see if you can clear the debris that way. Flushing it the normal way of flow won't move the blockage you see. Its going to be time consuming I'm afraid. BUt i would say that once the blockage is cleared then you will have heat again.

Thank you again


Customer: replied 2 years ago.
Dear Nathan,Thanks again for your help which is truly excellent.I have spoken to VW customer services and they want the car to go back to the same main dealer. The dealer is collecting it tomorrow morning.As you say, the source of grit in the expansion chamber is probably from the silica bag. However, in the stained expansion chamber they have given to me, the silica bag is intact. If it does have a very small hole, any loss of content would be less than a teaspoon.Please can you tell me why VW put a silica bag inside the expansion chamber because if it leaks, it does so much damage. Since antifreeze has silica in it anyway, surely the risks of the silica bag outweigh any benefit?Please could you tell me where the oil that I have found in the expansion tank could possibly have come from?Best wishes,John

Hi John.

Once again, i am glad i can help you through this because it can be frustrating i know.

Ok, well the reason they put the bag in is to keep a constant level of silica in the system. The bags very rarely break as i have never dealt with one breaking myself, nor have any of my mechanic friends that i have spoken to. So they obviously think that it is worth putting it in to stop corrosion. I don't think that the grit in the tank is from the bag though because it is brownish like sandy grit and the silica is white. Also as i don't think that that tank is off your car as you would have noticed the staining before and they don't stain over night, but the oil could have come from the oil cooler when they found the leak there and changed is as the oil cooler has coolant pipes going through the system as part of the coolant system. so the oil could have cross contaminated at the oil cooler.

I'm sort of glad that they are going to try again to fix it, but i just hope they do and i'm wondering if they are going to charge you for it or do it as a good will gesture as you are already out a small fortune to them and no further on.

Please keep me posted about what they say and i am here to give you any advice you need.

Thank you again


Customer: replied 2 years ago.
Thanks Nathan, I'll keep you posted. When this is finished I'll write an excellent review for you.Please could I just ask how cross contamination occurs in the oil cooler. I understand how this occurs when a cylinder head gasket fails, but how would oil in the oil cooler get into the coolant - is there a seal that fails?Best wishes,John

Hi John.

Cross contamination would happen if the rubber seal or metal gasket failed where the cooler is bolted on to the engine and the oil and coolant could mix slightly through the channels. But as I have said and I'm not trying to Blacken the dealer's name as I don't know them but I don't think that that bottle has come from your car because of the staining but I may be wrong. And that could be why they changed the cooler.

I look forward to your result.

One last thing though. it may be worth asking them if they could back flush the matrix and see if that cures it at all.

Best wishes


Customer: replied 2 years ago.
Dear Nathan,I think they are taking it seriously as they collected my car at 7.30 this morning and called me at 5pm to say tlhey were still working on it. Hopefully they will back flush as requested.They have loaned me a top notch Passat !I'll keep you informed and many thanks for everythingBest wishes,John
Customer: replied 2 years ago.
Dear Nathan,Well, they still have my car at the main dealer (another 3 full days so far). They are puzzled by what has happened and have discussed with VW head office who have told them to keep flushing the cooling system.They say that the brown stuff keeps coming out when they flush (including back flushing) - the same stuff that we saw in the old expansion bottle.We are just wondering if this is a design a design fault with the Mark 7 Golf because I bought one of the first. There are very few other mark 7 Golfs on the road that have already done 60,000 miles and perhaps in another year or two they will all start developing the same problem. Time will tell.The main dealer has been informed that there was one other mark 7 recently that had the same problem at another garage.Nathan, I have not shown or mentioned any of your feedback to anyone and I don't intend to. It's purely between me and you and for my information only. I would never pass your comments onto a third party without first getting your permission in writing.The dealer thinks that the silica from the bag could have caused a chemical reaction in the coolant system to cplreate the brown gunk.Please could you tell me, in your opinion, where you think this brown contaminant in the cooling system could possibly be coming from?Also, how long have VW been putting the silicone bag in the coolant expansion chamber - is this a new thing for the mark 7 golf?Many thanks again,Best wishes,John

Hi John.

Sorry for the delay in my reply this time, I was away all day yesterday and unable to get online for any length of time to reply to you properly.

All i know about the silica bag is that it was first used by Mercedes about 8-9 yrs ago and they have found it to be ok within their systems thus far. As far i am aware from speaking to an ex vw mechanic friend of mine is that VW have only really used it the last few years and he himself never saw or dealt with a bag breaking in the coolant system and causing a chemical reaction. You would think that they would have done tests to find out what happens if the bag breaks and be able to say that this is definitely from a chemical reaction with the coolant, and to be honest, as the coolant has silica in it already why doesn't the coolant do this all the time. It is hard to say where this sludge is coming from without obviously being able to see the car for myself, but as i have said before it seems to be a kind of rusty kind of colour as though something has corroded within the system and so causing this to keep rising up. The head of the engine is alluminium so this wouldn't cause this colour of sludge and the block of the engine as far as i know is cast so channels inside this may have corroded and cause this colour of sludge but i would very much doubt it is this. It may be that oil is getting into the coolant system somewhere where the channels are close and a seal has failed but in my opion this wiuldn't cause the grittyness in the sludge as it would just cause the coolant to get kind of creamy/brown. So either this was an additive that was added to the system and is now coming back to haunt them or it is indeed residue left over from the bag breaking. In both cases though this should eventually cease to rise up after enough flushing as either the bag residue or the additive is now not being put into the system. If it continues to rise up then there is a part within the engine/coolant system that is breaking up with corrosion and this needs to be found and sorted.

One question from me though John. As they say this problem has occured with another car at another dealer are you able to chat to the other dealer at all to find out if they found an answer and as VW now know of the problem are they going to sort it as a goodwill gesture and what about the costs you have already incurred from this problem where the dealer has charged you a lot of money. Are they going to refund some if not all of this as it is a problem with the car and not something you have done yourself.

I hope this helps you John, but i will do some more research for you and see if i can come up with anything else that might help and anything i do come up with i will post on here.

Thank you again


Customer: replied 2 years ago.
Dear Nathan,Thanks again for your very helpful information which I really appreciate.Well, they phoned yesterday to say that they are still not happy with the car. As I am away next week they told me to use the rental car for the whole week!They are still flushing it and getting brown gritty stuff out. They are going to change the heater matrix again!Concerning a rebate, they say the car is out of the guarantee period (by 3 months) and so any problem with the car after that is my responsibility. They are only responsible for faults identified during the warranty period and not afterwards.Please find out as much as you can for me about the possible origin of this gritty brown stuff that destroys the heater matrix, water pump (makes the metal sleeve stick over the impeller) and the inlet manifold as the dealer cannot offer a satisfactory explanation other than to say it's a little bit of silica from the bag in the expansion chamber that has caused a chemical reaction. I don't believe that?Concerning the car with the same problem at the other garage, they say they changed the heater matrix nearly a year ago and have not seen the car since. Presumably the owner sold it!Best wishes,John