2018 Q5 2.0 TFSI - Coolant leak?

[7heGeneral]

Hi all,

I've got a 2018 Q5 2.0 TFSI and over the last few months I've noticed a coolant leak. I dont know where it's going (I can't smell it inside), but It has gone to below the min marking a couple of times resulting in me having to top it up.

I've had the Waterpump & Thermostat changed - I thought it was going to resolve the issue, but unfortunately that hasn't helped.

I also notice that my heating does not get very hot, it is luke warm at best & certainly not as hot as it used to be.

Occasionally after a drive if I want to top up the coolant, when opening the expansion tank lid the level does rise and I get some leaking out from the overflow pipe.

Anybody have any ideas what I could check or need to replace to resolve this?

I'm pretty handy with the spanners so have no qualms with tackling this, but I was hoping somebody has tackled this problem before and was able to point me in the right direction before I start throwing parts at it.

Thanks again

[thebraketester]

Any white smoke from exhaust?

[stevemcs]

Did the pipe at the back of the thermostat get replaced ? Given it doesn’t get hot are you sure there isn’t an airlock

[7heGeneral]

thebraketester said:

Any white smoke from exhaust?

Nope, no smoke & the oil/coolant seem fine. It drives absolutely fine, doesn't ever go over the midway point on the temp gauge. Just a coolant leak with very little heating are the symptoms.

[7heGeneral]

stevemcs said:

Did the pipe at the back of the thermostat get replaced ? Given it doesn t get hot are you sure there isn t an airlock

Unsure about the pipe at the back tbh.

I was told the system is a "self bleeding" one - so if there was, shouldn't it be resolving itself? When I open the coolant bottle, it does bubble up, so could that be an airlock? I was thinking it could be the heater matrix possible being blocked, but I wanted to see if there was anything I could check before I take the dash apart.

[thebraketester]

7heGeneral said:

Nope, no smoke & the oil/coolant seem fine. It drives absolutely fine, doesn't ever go over the midway point on the temp gauge. Just a coolant leak with very little heating are the symptoms.

Odd.

No gunk under oil cap? What do the plugs look like? I presume there are no visible leaks?

The temp gauge should sit at 90oC on the dial so that seems fine.

[7heGeneral]

thebraketester said:

7heGeneral said:

Nope, no smoke & the oil/coolant seem fine. It drives absolutely fine, doesn't ever go over the midway point on the temp gauge. Just a coolant leak with very little heating are the symptoms.

Odd.

No gunk under oil cap? What do the plugs look like? I presume there are no visible leaks?

The temp gauge should sit at 90oC on the dial so that seems fine.

I'll double check the oil cap, but last time I checked, there was no mayo. The plugs have been changed ~9 months/~7000 miles ago at Audi as part of a service so I'd assume they're still good.

No visible leaking, except for the leak from the overflow pipe on the coolant bottle when I open the expansion cap whilst the engines still warm.

[Dr G]

As already suggested I'd be re-checking the thermostat, it can be a slightly fiddly job. There's a plastic t-piece near there too that can split/leak. What colour is the coolant? Should be fairly bright pink, any sign of it turning brown/murky? I'd look at heater matrix too, common on MQB cars but may be some commonality.

[7heGeneral]

Dr G said:

As already suggested I'd be re-checking the thermostat, it can be a slightly fiddly job. There's a plastic t-piece near there too that can split/leak. What colour is the coolant? Should be fairly bright pink, any sign of it turning brown/murky? I'd look at heater matrix too, common on MQB cars but may be some commonality.

Thanks Doc - i’ll double check the thermostat/waterpump. It did come with a t piece & the garage i used for the job has a good rep, so i’m hoping that is ok.

The coolant is still pink - could the bag inside have burst & caused my heatermatrix to block? Is there any way to check the heater matrix without taking the dash out?

Thanks again

[stevemcs]

Did they use a genuine pump and thermostat ? did they replace the waterpump gasget, the part right at the back where it goes into the cooler is a straight pipe with 2 o rings.

[7heGeneral]

stevemcs said:

Did they use a genuine pump and thermostat ? did they replace the waterpump gasget, the part right at the back where it goes into the cooler is a straight pipe with 2 o rings.

I supplied a INA waterpump & thermostat. It came with a belt, the little plastic piece and the o rings required. As far as i know INA are a reputable brand which is why i chose it.

[Dr G]

Genuine water pump is Saleri (Italy), genuine thermostat is INA (Czech). I've just had a couple land on my desk straight from TPS.

I have seen the little pipe fitted incorrectly and leak (06L121131) and you need 2x N90765301 seals too. None of those will reseal if reused.

...and it is of course possible that it's something entirely different. Common early sign of unhappy heater matrix is uneven heater temperatures side to side. I've evne seen one blocked with casting sand from the engine block!

[budgie smuggler]

7heGeneral said:

Thanks Doc - i ll double check the thermostat/waterpump. It did come with a t piece & the garage i used for the job has a good rep, so i m hoping that is ok.

The coolant is still pink - could the bag inside have burst & caused my heatermatrix to block? Is there any way to check the heater matrix without taking the dash out?

Thanks again

If you've got the one with the bag in, get it swapped for the one without anyway, and ask them to check the bag hasn't split on the old one.

[Discombobulate]

budgie smuggler said:

If you've got the one with the bag in, get it swapped for the one without anyway, and ask them to check the bag hasn't split on the old one.

I just took the bag out of mine. Tricky but possible with needle nosed pliers. Just don't burst it