My 2014 Octavia TDI SE has been losing coolant. Light came on and was diagnosed by first mechanic as leaking water pump, which was replaced at some expense. Coolant light is still intermittently coming on, with loss of coolant. Two more trips to the mechanic, plus a second opinion. Pressure test revealed no leaks. When the light has come on on a journey and I have had to top up I have found coolant pooling under the expansion tank (see photo). Is this possibly a leak from the tank or from hoses/seals located near. And why has this not showed up on a pressure test? This is now a three week saga and I suspect the water pump replacement might have been unnecessary. Any advice would be gratefully received. 

 

 

Edited 11 August, 20223 yr by SVBurgess
Better picture

Check the hose under the tank and make sure the lid and pressure cap are in good Nick 

51 minutes ago, SVBurgess said:

My 2024 Octavia TDI SE

Shouldn't this be a 2014 model?

1 hour ago, cheezemonkhai said:

Check the hose under the tank and make sure the lid and pressure cap are in good Nick 

 

And if they are, amongst other things it might be an idea to have a sniff test completed, to see if the engine is pressurising the cooling system.

 

I see the current tank has 'Mit Silikat' on it.  It'd be an idea to check if it has the silicate bag in it, whether it's intact (a cause of coolant system blockages if it ruptures) and get it removed.  If that's coolant residue just below the mit silikat symbol, it could be a sign the coolant is coming out the tank's lid.

 

Gaz

 

PS: if you've not already seen them:

 

 

 

 

 

Edited 11 August, 20223 yr by Gaz
added a couple of links

1 hour ago, john999boy said:

Shouldn't this be a 2014 model?

Yes! Sorry!

5 minutes ago, SVBurgess said:

Yes! Sorry!

BTW, as a freedom subscriber you have an unlimited amount of time to edit your posts. 👍

Thanks for all advice. Have just had new header tank fitted - hope that this will have solved the problem🤞 (although not entirely confident in the light of the many apparent weaknesses of these coolant systems!) 

Despite brand new header tank, the same problem (coolant disappearing from tank after first substantial -100 mile - motorway drive and visible pooling of coolant under tank and spots of coolant around tank) has occured again. No sign of any coolant leaks elsewhere in engine/under vehicle.
Coolant - what’s left of it - is clean. As is the oil in the engine. Car ran just a little hotter than usual towards the end of the drive - 101 - 103 C, but did not overheat. 
Any ideas? This is proving very frustrating - and I seem to have just shelled out for two unnecessary jobs! 

Edited 21 August, 20223 yr by SVBurgess

Only ways you'll have leaking coolant visible there is a bust pipe or cap... Was the cap changed with the new tank? If so then likely it's a small pin hole or hairline fracture of a pipe either side of the tank that only shows when the system is hot.

 

Get a new cap if needed and change the 2 pipes either side of the tank then reassess.

Where the coolant is seems to indicate it's coming from the expansion tank cap/lid.  It's a good shout by Jack to get a new lid, as that might make it an easy fix - best to start with the easy/cheapest solutions.  Have you had the bonnet up with the engine running, at temperature; it might become obvious with just a visual check.

 

That there is no oil in the coolant, or vice versa is a good sign.  Unfortunately it's also not conclusive, so a sniff test to check the coolant for exhaust gasses might prove reassuring.  Sounds like it needs further diagnosis as to what's going on (if it's not the cap).  A stitch in time, and all that jazz...

 

Gaz 

The lid is brand new as well as the tank, so unlikely to be those. Currently being investigated again at the garage that fitted them, so we’ll see 🤞

Have been told there was an electrical fault to the valve on the tank which was preventing correct opening of valve when coolant hot/under pressure. Allegedly now fixed - but I’m still a bit sceptical!  

Perhaps they could show you what valve on what tank 🙄

 

Fixed is what counts.  Could have been a wiring fault or a plug not plugged in to a temperature sensor, or the water pump/another part of the cooling system.

 

Fingers crossed it's sorted and the saga draws to a close.

 

Gaz

 

I’d be very interested to know how this goes, and especially what valve was causing the problem if it is now fixed, as I have had this issue for well over a year even after several new coolant header tanks and even more caps. Never been majorly worried because I can see exactly where the problem lies but it is a pain topping up coolant every other week…

There's no valve on or near the header tank? Hmm... I think you'll probably find it still leaking in the near future based on your mechanic.

Only electrical valve is the sleeve on the water pump which does fail a lot but wouldn't spit coolant out of the bottle or very close to. Have you noticed coolant pooling under the car or leaking elsewhere except by the tank?

Overpressure of the system will vent by the tank cap if it's working correctly so you could have an air lock or some other form of blockage...

No coolant spilled anywhere else than the tank - I agree that the problem must be caused by over pressure and venting at that point.

I’m also quite sceptical too, and I’m obviously not a mechanic, so It would be more than possible that I have misunderstood the most recent diagnosis or am being fed a line! But i’m taking it back in on Thursday (having given it two long motorway runs) to see if the error code that came up is still clear (and to report any further leaks, if they happen!) so I’ll find out the specifics then (of the code and the valve) and post them. 

Managed a 100+ mile round trip yesterday with no incident, but far too soon to say if anything has really been solved. There have been false dawns before and I’ve already almost resigned myself to a future of regular topping up rather than spending time and money on trial and error repairs! 

Think positive - it's sounding good so far 

 

It'd be interesting to know what the error code was, as this might point to where the problem was specifically.

 

My 2015 vRS had a fault on the Coolant Check Valve.  Didn't boil over or overheat, but it did cause the turbo to grenade itself due to a lack of coolant, which was an expensive fix ☹️

 

Gaz

 

On 24/08/2022 at 09:40, SVBurgess said:

No coolant spilled anywhere else than the tank - I agree that the problem must be caused by over pressure and venting at that point.

I’m also quite sceptical too, and I’m obviously not a mechanic, so It would be more than possible that I have misunderstood the most recent diagnosis or am being fed a line! But i’m taking it back in on Thursday (having given it two long motorway runs) to see if the error code that came up is still clear (and to report any further leaks, if they happen!) so I’ll find out the specifics then (of the code and the valve) and post them. 

Managed a 100+ mile round trip yesterday with no incident, but far too soon to say if anything has really been solved. There have been false dawns before and I’ve already almost resigned myself to a future of regular topping up rather than spending time and money on trial and error repairs! 

Hello, did you fix the problem? Do you still have any issues ?

thanks

sM

I have the same problem and got the rad replaced no joy. Was told there was another small rad at the front of the engine that is prone to slow leaking, a camera needs to go into a pipe to verify and if its the case it needs to be replaced. Expensive job if so.

Sounds like they’re referring to the charge air cooler 

I had the same symptoms on my son's 2014 2.0Tdi A3, I think the same engine. It turned out to be the heater matrix starting to get blocked. A tell tell sign apparently is that the drivers side stops blowing hot air. I changed the matrix and it has been fine since. From research it appears that when a regeneration occurs the pressure gets too high due to the partially blocked heater matrix and the extra pressure forces coolant out of the expansion tank and it pools around that area. 

10 hours ago, SteveOctavia19tdi said:

I had the same symptoms on my son's 2014 2.0Tdi A3, I think the same engine. It turned out to be the heater matrix starting to get blocked. A tell tell sign apparently is that the drivers side stops blowing hot air. I changed the matrix and it has been fine since. From research it appears that when a regeneration occurs the pressure gets too high due to the partially blocked heater matrix and the extra pressure forces coolant out of the expansion tank and it pools around that area. 

I'd read this somewhere when investigating my Coolant Loss, After trying nearly everything else!

 

How much did the Matrix cost to replace? did you do it yourself!? or did you get it done at a garage?

 

Was the Header Tank done at the same time? (a Non 'Silikat' one) does the system need flushing??

 

I just really want to know what I'm getting into before I do it/get it done!!

 

Cheers!!

The matrix was something under £100 (Nissens). I did it myself based mainly on this youtube vid having watched a few others for extra info. It took a while but wasn't too difficult. I clamped the heater pipes in the engine compartment so didn't lose too much coolant. I didn't do anything with the header tank nor flush the system as it looked pretty clean. I did have a slight leak on the lower joint for a few weeks after - the solution was to remove the clamp (I had refitted the Audi one) and used the nissens clamp having bent the tabs in a bit to ensure it was really tight,

Having thought more about it I've remembered that I didn't change or flush the coolant because I had done the water pump and cam belt the month before so the coolant had been replaced then. Having looked on youtube there are videos for changing the heater matrix on the octavia, looks pretty much the same, just less stuff to remove to get to it.

On 11/08/2022 at 07:21, SVBurgess said:

My 2014 Octavia TDI SE has been losing coolant. Light came on and was diagnosed by first mechanic as leaking water pump, which was replaced at some expense. Coolant light is still intermittently coming on, with loss of coolant. Two more trips to the mechanic, plus a second opinion. Pressure test revealed no leaks. When the light has come on on a journey and I have had to top up I have found coolant pooling under the expansion tank (see photo). Is this possibly a leak from the tank or from hoses/seals located near. And why has this not showed up on a pressure test? This is now a three week saga and I suspect the water pump replacement might have been unnecessary. Any advice would be gratefully received.