I'm struggling with my brother's 2.0Tdi Octavia, 2014 CKFC and would appreciate some help.

He was getting fairly regular low coolant warnings and was having to top up. I'd had similar with an A3 and in the absence of any leaks, and with clear evidence the coolant had blown out of the expansion tank I changed the heater matrix but that didin't make any difference. I have also bled the cooling system thouroughly several times using vcds which hasn't helped.

The symptoms seem to be:

No sign of any leaks anywhere apart form obvious high pressure forcing out coolant at the expansion tank.

The level remains fairly steady then will suddenly drop after a longer drive. On these drives there have been occasions when the in-car heating suddenly seems to get hotter.

No loss of performance and it never overheats.

No white smoke from the exhaust.

Heater matrix changed and coolant replaced.

Heated works fine, both sides.

Bled several times using VCDS.

Sniff test at the expansion tank showed combustion gasses present.

I'm thinking when the regeneration occurs it creates too much pressure, either due to partial blockage or more likely exhaust gasses leaking into the cooling system, leading to pressure release and coolant loss at the expansion tank.

From what I have read a failed ecg cooler is a likley cause, so I thought I would have a go at changing this. However having started the job it is looking even harder than I thought! I'm beginning to think I won't be able to remove the egr cooler - especially as it is 4x4 giving even less access. I wondered if I could bypass the cooling by joining the two egr hoses together then see if the symptoms persist. If I did this would it be ok to drive for a while with the egr still functioning but without its cooling?

Or can anyone suggest a better course of action or other things I should be doing first?

Yes, give it a try.

Thanks Pete.

I've been having another go at it and having removed more stuff I have actually managed to get the erg cooler off from above, I didn't need access from underneath in the end. I've done the pressurise underwater test and there are no leaks that I can see so it may well be ok after all. However, I shall replace it with a new one just to be sure, and I don't fancy doing the job again any time soon!

Pretty sure the egr is closed during a Regen so shouldn’t be impacting the coolant circuit. The charge coolers are notorious for failing on these also. Probably worth checking that

Thanks T07. From what I read the egr opens after regen adding a surge of heat through the egr cooler which causes the boiling /increase in pressure if the flow is restricted or air locked or gasses have leaked into the circuit.

I got it all back together, thoroughly bled all circuits and went for a spirited drive. All seemed ok, so after half an hour I did a forced regen whilst driving. This lasted about 10 mins and after another 5 mins or so driving to cool down I checked the coolant. There had been some loss at the expansion tank but not loads. Another sniff test showed combustion gasses again. So I think as you suggest, the charge cooler is the next thing to look at. I shall first try a pressure test on it in situ as it's easier to get to than the egr cooler.

There’s good access through the temperature sensor for a camera too to see if it’s leaking. Could clearly see water drops in mine