Sorry for the longish post. Cutting a very long story as short as possible, over the last 18 months my Octavia has been into the dealership a few times in order to investigate sudden coolant loss.

 

The first time, the timing belt and water pump were changed, which were more or less due anyway, and this seemed to improve the situation for a few months. However, on a longish holiday it recurred. The car went back to the dealership and, according to the "debrief" they gave me, they ran all the suggested tests and came up with no solutions. They agreed that they could replicate the coolant loss with the engine at high temperature, but had no idea where it was going or what was causing it. At one point they had the car for well over a week, leading to an extended discussion about how much I should be charged for them failing to diagnose a fault on a vehicle under warranty.

 

Anyway, after the last time it was in, I decided to run it for a bit and see what happened. At one point I was in a position to stop when the alarm went off, and found water inside the engine bay and down the wing. Over several thousand miles it became clear that although the header/expansion tank lost a lot of coolant quite suddenly from time to time, a reasonable amount remained below the level of the warning contacts, and the engine temperature didn't suffer at all. This made me think that the problem was with the tank itself, as the rest of the system seemed to be working fine.

 

Last week I changed the tank, noting as I did so that a small amount of the new coolant leaked out of the valve on the side. The level settled for a few days and all seemed OK. Then, one morning and without the engine being under massive load or heat, the alarm went again as I was leaving the house. This time it was clear that the coolant had vented from the same valve, as it was sat round the central rim of the tank and pooling on the inside of the wing.

 

I'm not particularly knowledgeable mechanically, but I can use a bit of logic, and it seems that something is tripping that valve, which I would assume is excess pressure in the system. Does anyone have any experience of what that might be?

11 minutes ago, bq15 said:

it seems that something is tripping that valve, which I would assume is excess pressure in the system. Does anyone have any experience of what that might be?

Excess pressure in the coolant system to me suggests that the coolant system is being pressurised from one of the cylinders, which suggests a head gasket problem (or in the much less likely worst case a crack in the head or block).

Agree with SWBoy.  For the alarm to have gone as soon as you've left the house, I'm a bit surprised something hasn't shown up on a sniff test, presuming the dealership would have thought about this being a potential cause.

 

Gaz

Thanks. I think a different dealership might be the next course of action.

I have the exact same issue... water pump failed catastrophically in the end before replacement under warranty. This stopped the coolant leak for a while, but now requires top up every 2000 miles; been looked at by two different dealerships and neither can figure it out. 

 

Coolant loss is worse when wife uses the car for lots of short journeys - another common failure is a coolant leak via the EGR, with coolant loss via the exhaust side of the engine.

Probably worth contacting Skoda customer services to discuss the ongoing problems you have with the car. It's not really good enough for a dealership to reproduce the fault but then not provide a fix. 

If you know of anyone with a Go-Pro or similar and can reproduce it then borrow it and fit it under the bonnet and record it happening. If you know someone with VCDS then I am not sure but I’d guess this can record live data when the engine is running then get this logging at the same time and you have evidence to share with anyone you want to escalate this issue to

Hi. I also have a 2013 new model Octavia vrs 2.0tdi 86 thousand miles.  with coolant leak.timing belt and water pump have been changed.  Can’t find the leak anywhere. Takes about half a litre every week. I’ve heard about egr problem and coolant going out the exhaust.  Anyone any help please. Thanks