2007 A3 1.9tdi Coolant Problem

[Sannasalter]

Ive had an ongoing issue for around 6 months now. Started out with the red flashing coolant light coming on for 10 - 20 seconds on a cold morning with the heaters taking about 20 minutes to get hot. No coolant loss at first. 

This then worsened to the point of the coolant tank emptying from full after about 10 minutes of driving. Have had a go at clearing an airlock a few times now but the problem comes back sometimes slowly sometimes immediately. The heaters now hardly work at all, sometimes luke warm but mostly just cold air. Used to make a sloshing noise from behind the glove box but as symptoms have worsened the noise seems to have gone away. 

The thermostat and water pump replaced. And the radiator and heater core flushed by a mechanic friend, he is unsure what the problem is now. 

Garage has told me they think its the heater core however my mechanic friend seems to think it isn't that as it is the g12 non sachet version. 

Im starting to loose patience with the issue and cant justify spending much more if it won't solve the issue. 

Any advice would be massively appreciated. 

 

Thanks. 

Edited April 1, 2023 by Sannasalter

[Sannasalter]

Also now when i put more coolant in it just disappears, no signs of a leak anywhere. Overheats after 30 - 40 minutes of driving. 

[Steve Q]

My two potential theories is that it is the heater matrix. 

Or the one thing you've not considered is a failing expansion tank cap. The seal can fail causing the water to escape. Also check the expansion tank for leaks around any joins in the plastic. 

[cliffcoggin]

A sloshing sound from within the dash and a lack of cabin heating are classic symptoms of air in the cooling system, so I suggest you have an airlock and/or a blocked heater matrix. The lack of circulation would cause localised boiling and ejection of coolant, hence the rapid loss, particularly if the tank cap is not sealing as Steve suggests.

[Magnet]

Hello Shanna,

So is the overheating issue, a new issue, or did it overheat prior to fitting a new thermostat? 
Have you had the coolant system pressure tested? 
Any undue smoke from exhaust once the car reaches operating conditions? 
Petrol or diesel as a matter of interest? 
Kind regards,

Gareth. 

[Sannasalter]

Thank you so much for your replies. Have already had a new cap fitted and the overheating is a new issue.

 

System has been pressure tested no signs of a leak. No smoke and its a diesel. 

Edited April 2, 2023 by Sannasalter

[Magnet]

You are very welcome Sanna. Logic points to confusion if the cap is sound, the system isn’t indeed over pressurising, there aren’t any leaks. So where is the coolant disappearing to? 
Overheating being a new issue:- since fitting the replacement thermostat? If so, I would be testing the new thermostat before getting into further investigations. 
Kind regards,

Gareth. 

[Sannasalter]

Coolant used to circulate though the system just very slowly. Now it doesn't seem to at all. 

 

[Magnet]

 Water pump might be suggested. Personally, I’ve never experienced a failed-to-circulate water pump without associated noise. 
Back to stuck thermostat?? 
Kind regards,

Gareth.