Coolant loss from tank on motorway journeys or high speeds

[LouG]

Even a small leak of combustion gases will over pressurise the expansion tank and blow out coolant. I've seen it on many cars that have run fine without other symptoms. But a test for combustion gases in the cooling system would show if that is happening.

 

[YKFR]

Based on your update - have you tried just leaving it (rather than topping it up) and see if it settles at some lower level. Obviously you need to keep an eye on things, but if you check it at the same time every morning you'll be able to monitor closely.

I had to fill it up to the minimum line as all of the coolant had been depleted. However, it has already begun to rise as the coolant has gone past the minimum line. I want to catch it in action to see how far past the max line it actually goes before leaking.

 

[YKFR]

Three things I know of that can cause that.

Thermostat, Water pump, head gasket/head failure.

Thermostat can be ruled out if you're getting hot air through the heaters.

I'd argue the head gasket could be ruled out if you've had a pressure test without any failures? Youd also be getting a misfire.

Water pump could be sitting without the fins on the back of it, yet not bad enough to leak. The water will be sitting still, overheating due to not being pushed through the radiator, and then boiling up in the header/expansion tank much like how a kettle works.

The header/expansion tank has a "leak off" at the very top, which allows coolant to drain out if the level reaches the cap. You can see this if you remove the cap and pour water down the thin groove where the caps screws into.

There is definitely hot air coming out of every air vent on every different air setting. The pressure test was done and came back negative both times from different dealerships. Water pump had been changed by the company in March 2019. However, they said if it was the pump it would show different symptoms? If I get the water pump checked then I'd be paying again to have the car stripped and if it isn't that then it will be a waste.

Also I know of the pressure release thing you are referring to. There is a hole near the cap where the cap locks in. Coolant is allowed to escape if there is too much pressure build up.

 

[Skilledmilk]

I urge you to have a skim through this forum thread: http://forums.tdiclub.com/showthread.php?t=483783

I have the same 184 seat with the overflowing issue and have remedied by changing matrix. There were never any leaks of coolant around the matrix and it did provide warm air albeit not hot. After changing the matrix the air is HOT and I've had no overflowing since (approx 2000 miles).

Car is 63 reg, 142,000 miles

Sent from my ONEPLUS A3003 using Tapatalk

 

[YKFR]

I urge you to have a skim through this forum thread: http://forums.tdiclub.com/showthread.php?t=483783

I have the same 184 seat with the overflowing issue and have remedied by changing matrix. There were never any leaks of coolant around the matrix and it did provide warm air albeit not hot. After changing the matrix the air is HOT and I've had no overflowing since (approx 2000 miles).

Car is 63 reg, 142,000 miles

Sent from my ONEPLUS A3003 using Tapatalk

Hi,

Thanks for your reply. I do think its my heater matrix now that I have had the car for over 3 months. Surely with the issue of head gasket or engine head being cracked the problem would worsen a lot more and quickly. But my car has not given me any issues. The coolant has also not dropped in over 3 weeks.

Someone else on another forum was having same issue as me and they replaced the heating matrix and their problem is gone. And now you too.

I wanna know how much did it cost you to get a new matrix? And coolant flush? What was the total price for that? And where did you buy a new matrix from. Also if you do long motorway journeys at high speeds of 80+ at times to test the remedy? Thanks.

 

[Skilledmilk]

I bought the matrix online, £80ish. I'll have a check when I'm home where I got it from. The consensus from the forum thread I linked is that the overflow is related to the restricted flow through the matrix. It's not an issue in day to day driving but the increased flows needed after a dpf regen cause an overflow. Which probably explains the sporadic nature of your issue also.

I think local specialist garages would charge around £300 but if you fancy having a go yourself you can do it for part cost only.

I've had no overflows and I do a mix of relaxed motorway and 'spirited' driving at weekends! Since the replacement I've not lost any coolant.

I still do recommend a read through that forum thread, there's been lots of diagnosis and troubleshooting to arrive at the matrix as the problem.

As an aside, I lived with this problem for about 30-40 thousand miles, relieved to have a solution is an understatement!

Sent from my ONEPLUS A3003 using Tapatalk

 

[YKFR]

I bought the matrix online, £80ish. I'll have a check when I'm home where I got it from. The consensus from the forum thread I linked is that the overflow is related to the restricted flow through the matrix. It's not an issue in day to day driving but the increased flows needed after a dpf regen cause an overflow. Which probably explains the sporadic nature of your issue also.

I think local specialist garages would charge around £300 but if you fancy having a go yourself you can do it for part cost only.

I've had no overflows and I do a mix of relaxed motorway and 'spirited' driving at weekends! Since the replacement I've not lost any coolant.

I still do recommend a read through that forum thread, there's been lots of diagnosis and troubleshooting to arrive at the matrix as the problem.

As an aside, I lived with this problem for about 30-40 thousand miles, relieved to have a solution is an understatement!

Sent from my ONEPLUS A3003 using Tapatalk

Hi I think I'm getting somewhere with this issue. Today the coolant dropped even though I was doing like 20-25 mph. The difference was the the Fan was on and my resting revs were 1000. I assume the car was in regen mode, as the fan was on since yesterday but due to my short journeys the regen couldn't be completed yesterday.

Now I hope that this was a regen issue, so what you and other people have said is true and it's my heating matrix and not engine. Anyway I can make sure of this? Got any ideas?

Also can you link me where you got your heater matrix from? That would be of great help.

 

[Skilledmilk]

Myself and others noted that the coolant only overflowed on completion of the regen cycle.
Assumed that the coolant uses a separate circuit during regen heat up phase and on completion switches back to run through the egr cooler, cooling the exhaust gases back down again. Restricted flow in a partially blocked heater matrix slows down the overall flow and the coolant then boils due to the high exhaust gas temperature. Dashboard temperature readings don't change as I don't think the temperature sensor is near to the egr cooler.

What you've described in your most recent post and previous posts sounds identical to the numerous other cases, mine included.

If you have no oil/water mixing evident on the filler cap and no steam from the exhaust it is unlikely to be the head gasket.

I got my matrix online from autodoc, link below and made the swap myself. I don't know if the same would fit a golf (but my Leon is the same MQB platform) so it would be worth checking around for a specific part number.

https://m.autodoc.co.uk/nissens/7589648

Sent from my ONEPLUS A3003 using Tapatalk

 

[YKFR]

Myself and others noted that the coolant only overflowed on completion of the regen cycle.
Assumed that the coolant uses a separate circuit during regen heat up phase and on completion switches back to run through the egr cooler, cooling the exhaust gases back down again. Restricted flow in a partially blocked heater matrix slows down the overall flow and the coolant then boils due to the high exhaust gas temperature. Dashboard temperature readings don't change as I don't think the temperature sensor is near to the egr cooler.

What you've described in your most recent post and previous posts sounds identical to the numerous other cases, mine included.

If you have no oil/water mixing evident on the filler cap and no steam from the exhaust it is unlikely to be the head gasket.

I got my matrix online from autodoc, link below and made the swap myself. I don't know if the same would fit a golf (but my Leon is the same MQB platform) so it would be worth checking around for a specific part number.

https://m.autodoc.co.uk/nissens/7589648

Sent from my ONEPLUS A3003 using Tapatalk

Thanks for your detailed reply. I am very sure now its the matrix which is failing (and or the pipes are partially blocked). Also thanks for your link to the new heating matrix.

I just wanted to know that if your coolant was forced out of the tank during high speed short runs (probably on motorway). Because first two times it has happened when I had gone over 90 mph and found the tank empty. Let me know what you think about that.

 

[LouG]

Myself and others noted that the coolant only overflowed on completion of the regen cycle.
Assumed that the coolant uses a separate circuit during regen heat up phase and on completion switches back to run through the egr cooler, cooling the exhaust gases back down again. Restricted flow in a partially blocked heater matrix slows down the overall flow and the coolant then boils due to the high exhaust gas temperature. Dashboard temperature readings don't change as I don't think the temperature sensor is near to the egr cooler.

What you've described in your most recent post and previous posts sounds identical to the numerous other cases, mine included.

If you have no oil/water mixing evident on the filler cap and no steam from the exhaust it is unlikely to be the head gasket.

I got my matrix online from autodoc, link below and made the swap myself. I don't know if the same would fit a golf (but my Leon is the same MQB platform) so it would be worth checking around for a specific part number.

https://m.autodoc.co.uk/nissens/7589648

Sent from my ONEPLUS A3003 using Tapatalk

This sounds sensible. But why would a matrix block on a new car?

 

[Skilledmilk]

I hadn't noticed coolant loss on specifically high speed runs, only that it was following a regen. It's possible that your car completed a regen, although also possible that the high speed driving increased the water pump speed and caused an increase in pressure that way.

If you can discount any head gasket related issues then changing your heater matrix can be done pretty cheaply, especially if you undertake yourself!

Sent from my ONEPLUS A3003 using Tapatalk

 

[Skilledmilk]

This sounds sensible. But why would a matrix block on a new car?

A few on other forums have cited casting sand from the block casting process, others that the silicate bag in the header tank burst and released granules into the system.

When I changed mine there was significant resistance to flow through of air compared to the new replacement. The channels are very narrow so it wouldn't take much to restrict the flow.

As I said previously, after replacement the air from the vents is much hotter indicating that flow of coolant was definitely restricted. I've had no overflows or drop in coolant level since.

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[YKFR]

I hadn't noticed coolant loss on specifically high speed runs, only that it was following a regen. It's possible that your car completed a regen, although also possible that the high speed driving increased the water pump speed and caused an increase in pressure that way.

If you can discount any head gasket related issues then changing your heater matrix can be done pretty cheaply, especially if you undertake yourself!

Sent from my ONEPLUS A3003 using Tapatalk

Yeah I want to change mine my self but I am a newbie when it comes to that. Did you find it tricky to open it all up and put it back together? Was the coolant flush/bleeding the system difficult? And did you follow any specific video to do all that?

Sorry for all the questions I just want to be 100% sure with what I am doing in the future about this issue.

 

[LouG]

although also possible that the high speed driving increased the water pump speed and caused an increase in pressure that way.

Sent from my ONEPLUS A3003 using Tapatalk

No, the water pump is a displacement pump not a high pressure pump. It's only heat that causes coolant system pressure to rise.

 

[Skilledmilk]

No, the water pump is a displacement pump not a high pressure pump. It's only heat that causes coolant system pressure to rise.

Good to know, I think I had that confused with the oil pump then!

The replacement job itself is not too difficult, however I don't know how easy it would be to flush the system as I had a service lined up the following week where they would do it anyway.
The matrix can be accessed from the passenger side footwell if you have a right hand drive car. The trim up the side of the gearstick, the foot vents, blower motor and glovebox need removing to access but it can all be done with one hex screwdriver. On the face of it, sounds a bit of a task but I think it took about 2 hours all in. I could do it quicker if I ever had to do it again! I'll have a look for my own photos from the job and the workshop manual that gives a little more info on the tools/process.

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[LouG]

I should have added, a displacement pump will build some pressure when its outlet is blocked or partially.

 

[RUM4MO]

I can see that there is the probability for a slight bit of "dead heading" going on if part the system is being restricted more than normal as the heaters in these cars are meant to be running full flow at all times - as far as the circulating pump is concerned.

 

[YKFR]

Good to know, I think I had that confused with the oil pump then!

The replacement job itself is not too difficult, however I don't know how easy it would be to flush the system as I had a service lined up the following week where they would do it anyway.
The matrix can be accessed from the passenger side footwell if you have a right hand drive car. The trim up the side of the gearstick, the foot vents, blower motor and glovebox need removing to access but it can all be done with one hex screwdriver. On the face of it, sounds a bit of a task but I think it took about 2 hours all in. I could do it quicker if I ever had to do it again! I'll have a look for my own photos from the job and the workshop manual that gives a little more info on the tools/process.

Sent from my SM-T580 using Tapatalk

Thanks for being a big help in narrowing it down for myself. I just couldn't pin point why it was so 'random' but I guess it isn't so random afterall. This just shows that more minds are better than one at problem solving. Reading other forums and reading other peoole's issues have made it that much better for me.

And yes any other tips you can give me that can help with the procedure it would be great!

And now it kind of makes more sense as to why on a longer journey with high speeds under warmer conditions the coolant would rise, because there is more pressure build up.

I will have that job done soon. I just didn't want it to be my engine it self.

 

[YKFR]

I urge you to have a skim through this forum thread: http://forums.tdiclub.com/showthread.php?t=483783

I have the same 184 seat with the overflowing issue and have remedied by changing matrix. There were never any leaks of coolant around the matrix and it did provide warm air albeit not hot. After changing the matrix the air is HOT and I've had no overflowing since (approx 2000 miles).

Car is 63 reg, 142,000 miles

Sent from my ONEPLUS A3003 using Tapatalk

I have given my car in today to get the heating matrix replaced, full coolant flush done and expansion tank cleaned out. The garage didn't quote me too muc for the price. While driving there (14 miles), there is some travel on the motorway. So after I had driven fast and my radiator was was on for a while, I got to the garage and checked the coolant. Some had been forced out of the tank as it was wet around it....

Lets see what happens and what the garage says. Also there is a clear difference in temperature from two sides of the car when air is thrown out. One side is warmer than the other but both are not really hot hot...

 

[minu94]

@YFKR, any news? Did you get it fixed or do you have the same issue?