Very strange coolant leak!

[Gazcoedcae]

I'm loosing a tank of coolant in one hit approx every month. I'll get in the car and have an alarm warning me that the tank is empty. This has been going on now for about 6 months but the car drives fine with no low level alarms until the following day when the tank is empty. I've been keeping an eye on the level before and after every trip with no drop in level, then all of a sudden the following day it will have lost a whole tank. 

There's evidence that it's coming out from the cap, which has been replaced along with the tank. 

The heating has also become very poor (worse on the drivers side for some strange reason) so I removed the heater matrix expecting it to be blocked but that was free flowing with no leaks. 

Any ideas if the system can over pressurise itself and vent coolant through the expansion tank cap when the engine is switched off? 

I'm at a loss now and can imagine that if I take it in to a garage they won't find anything due to the sporadic nature of the problem. 

[Steve Q]

Sounds like you've done a good job, did you bleed the air out the system after all.tebwork you've done? 

[Gazcoedcae]

On 8/9/2020 at 6:10 AM, Gazcoedcae said:

 

System was bled and the level remained stable for a month. Had to fill it up again 8 days ago and again its stayed stable for a week. I'm wondering now if it could be related to the dpf regen in any way shape or form. I'm clutching at straws now! 

[Steve Q]

I'd get a diagnostic check carried out to see if any fault codes flag up. It's definitely not mixing with oil? 

[Magnet]

Hello Gary,

My first action would be to get the coolant system pressure tested. 

Kind regards,

Gareth. 

[Gazcoedcae]

System was pressure tested and all fine. Decided to change the heater matrix as a last resort. Seems to have done the trick despite being able to run water through the old matrix. Decide to cut open the old matrix and found it to be full of a murky sludge which definately would have reduced flow. Fingers crossed its solved this problem for good. 

[Steve Q]

Glad you've solved it 🙂

[CoventryAudi]

On 9/21/2020 at 3:04 PM, Gazcoedcae said:

System was pressure tested and all fine. Decided to change the heater matrix as a last resort. Seems to have done the trick despite being able to run water through the old matrix. Decide to cut open the old matrix and found it to be full of a murky sludge which definately would have reduced flow. Fingers crossed its solved this problem for good. 

Silica bag had split! Remove it before this happens!!!!!

[RicardoKaiser]

Hey mate!

The the problem you had resolved by replacing the heater matrix?

The car worked fine after that?

[Chr13]

Hi mate , I have just had the same problem , no warning signs or lights until I started my car this morning and a warning flashed up to turn off the engine and check coolant level. When I checked the level was almost empty so I’ve topped it up with water to see if I have a leak ( nothing as of yet ) but when I put the heating on it’s working fine on the passenger side but Luke warm on the drivers side , I haven’t had the system pressure tested yet but I’m hoping I don’t need the heater matrix replaced as I have been quoted around £350 just to strip the dash out and I am dreading to see the price after the part and installation, is that a requirement to strip the whole dash to get to the heater matrix?? 

[Scubayorks]

Hi, this is my first post and to confirm I have the same issue. Were the above fixed with the heater matrix?

Car has been pressure tested and no issues then all of a sudden it uses a bunch of coolant, I too have a lukewarm drivers side compared to passenger side. It’s refreshing to find someone else who has had the same problem

[Magnet]

Hello Chris,

Thanks for being in touch with the forum, and sorry to hear of your issue. 
If you are losing coolant (and it sounds as if it’s a considerable amount by your description) then logically it must be either be leaking (‘externally’) or being burnt by combustion. 
The leak may be from the heater matrix, and if it is, then there is going to be evidence inside the car/ under carpets. If there is a leak on the external parts of the coolant system within the engine bay, then it should be evident there. Normally pinkish deposits are a tell tale, but you could try laying paper under the engine compartment and seeing if there are any damp patches - obviously weather dependent test. 
If both of these are negative, then coolant may be leaking into the engine intervals and being burnt - so no external evidence of a leak.

A simple test is to take the car on a 10 mile run, then immediately on your return, get an assistant to rev the engine to a steady 2000rpm and hold it there for about 2 to 3 minutes while you observe the exhaust smoke - looking for grey vapour. 
Don’t ignore the fact that pressure testing the system ( to a greater than normal operating pressure) may have aggravated an already minor leak. 
Heater issues? May not be directly associated with the now coolant loss. 
Coolant loss now becomes your priority. 
Maybe worth sending a PM to the last poster.

Perhaps you could let us know how you get off with the above tests.

Kind regards,

Gareth. 

[Scubayorks]

Hi Gareth,

 

thanks for your great reply, I bought the car from a main dealer (non-audi) and have 1yrs warranty with the car so it’s been investigated to the point where it was booked in to Audi and they diagnosed that the heating issue on the drivers side was down to the flap motor but also saw a code for heater matrix and suggested this may need changing. From what I can see and feel the carpets are bone dry.

At the time they weren’t aware of the excessive coolant use so weren’t testing for that as since I topped it up it had been fine for 2 weeks then just yesterday I noticed it had shot down. 
 

i will give an update as soon as I have it though as the non-main dealer are liaising with Audi and claiming back under extended warranty and it looks like it’s going to be the defrost motor flap and heater matrix that get replaced, they quoted £1300 for the work did Audi so glad I’m not paying! 

[salimS]

I had similar problem

Car is Audi a3 Quatro 184bhp tDi

Found was loosing coolant intermittently

Changed coolant cap

Changed coolant resevoir 

Specialist suspected overheating but my temp guage always stayed in the middle

His suggestion water pump so got that changed 

Still same problem then he pressure tested it. Came back OK

Mechanic kept talking about overheating. I wasnt convinced I suspected overpressure. 

After a journey. Coolant level would be fine the next morning it would have gone. So i decided to leave the bonnet open let it cool down properly. Still coolant loss

Mechanic now talking EGR etc expensive....

Then i tried something that was suggested on the group blocked heater matrix.

Mechanic ggoedo you have a leak in the footwell. I didnt 

So I drove around for a couple of weeks NOT turning my heater on. Bingo no coolant loss

Got heater matrix changed and seems good now

So blocked heater matrix or partial blockage was causing a build up of pressure that eventually had to release through the cap via the hole in the tank 

 

Got genuine heater matrix from TPS. It a valeo. Autodoc sell it much much cheaper. Mechanic said dobt but it from Euro car parts as it doesnt fit 

[Guest]

On 8/28/2023 at 8:43 AM, salimS said:

I had similar problem

Car is Audi a3 Quatro 184bhp tDi

Found was loosing coolant intermittently

Changed coolant cap

Changed coolant resevoir 

Specialist suspected overheating but my temp guage always stayed in the middle

His suggestion water pump so got that changed 

Still same problem then he pressure tested it. Came back OK

Mechanic kept talking about overheating. I wasnt convinced I suspected overpressure. 

After a journey. Coolant level would be fine the next morning it would have gone. So i decided to leave the bonnet open let it cool down properly. Still coolant loss

Mechanic now talking EGR etc expensive....

Then i tried something that was suggested on the group blocked heater matrix.

Mechanic ggoedo you have a leak in the footwell. I didnt 

So I drove around for a couple of weeks NOT turning my heater on. Bingo no coolant loss

Got heater matrix changed and seems good now

So blocked heater matrix or partial blockage was causing a build up of pressure that eventually had to release through the cap via the hole in the tank 

 

Got genuine heater matrix from TPS. It a valeo. Autodoc sell it much much cheaper. Mechanic said dobt but it from Euro car parts as it doesnt fit 

Hi

I have replaced valeo heater matrix radiator under but I still have coolant leak and it dripping in the front in the middle between cooling fans and engine but I have no clue where from even if I checked with lamp ..