Audi A3 8V 2.0 TDI coolant loss and no heat in cabin

[serrobert]

Hello everyone, I'm looking for a possible solution to a recent problem I'm having with my A3.

It's a 2014 8V 2.0 TDI currently sitting at 163.000 km / 101.000 miles. Recently I noticed the coolant level not being consistent and no heat when using a/c.

I topped up the coolant to the "max" line (car cold) before a long trip I had to take (500 km / 310 miles). The next day (car cold again) the coolant was again under the "min" line.

Car was running fine the whole trip, without overheating with oil temperature in the 98-103 °C range (208-217 F). No heat in cabin the whole time.

I recently serviced the car and replaced diesel, air and oil filters, along with a full change of oil. Old oil was clean black and not contaminated - I'd exclude a failing head gasket.
Aircon controls works fine and putting it on max blasts cold air at full force.
Can't find any signs of leakage from the engine bay, might put the car up again and check from the underside.

My first suspect would be a clogged heater matrix. Any other idea?

 

[Fatbloke]

Any recent work done that would affect the cooling system?
Have you checked in the coolant expansion bottle for a burst silica bag?
Currently have an issue with my VRS where an air vent thermistor is faulty causing cold air on passenger side but only on one side so wouldn't have thought it was that. Maybe a vent pipe come off?
You mention no heat when using A/C, Is there heat when A/C is off? If so, I would think more an electrical than a physical issue.

 

[Sibmets]

Thermostat?

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[serrobert]

Thanks for your answers guys. I have a small update.

Thermostat?

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If it was the thermostat I'd have problems with engine temp, right? I did a pretty long trip and temp were stable the whole time. Even yesterday there were no fluctuations, with temperatures stable around 100°C/212°F.

Any recent work done that would affect the cooling system?
Have you checked in the coolant expansion bottle for a burst silica bag?
Currently have an issue with my VRS where an air vent thermistor is faulty causing cold air on passenger side but only on one side so wouldn't have thought it was that. Maybe a vent pipe come off?
You mention no heat when using A/C, Is there heat when A/C is off? If so, I would think more an electrical than a physical issue.

No recent works done that should affect the cooling system: I replaced the cabin air filter (same brand, correctly positioned following the arrows), the diesel filter, the oil filter and a full oil change.

About the update (and what makes me exclude the thermistor or vent pipes coming off), yesterday I went to the mall and drove the car a bit harder and got the following observations:
- temperatures were still stable without underheating or overheating
- on the trip to the mall I suddendly got hot air! working perfectly again on both sides with hot air on HI and cold air on LOW
- on the trip back no hot air again - sad.

Didn't get home but once stopped I checked the engine bay and there it was coolant everywhere under the reservoir tank! Coolant pipe going inside the cabin was very hot. Unfortunately I wasn't at home so I could only assess this. Today I'll get back home and check with a better light.

Plan is to inspect the reservoir tank for burst silica bag as suggested by Fatbloke and for any cracking in the reservoir or damaged reservoir cap. Will keep updated.

 

[serrobert]

Update for whoever finds this thread in future.

Apparently my expansion tank is a different revision and has no physical silica bag inside. So no burst silica bag. Also checked with VCDS for errors but aircon unit had no faults.

I ordered an original Valeo heater matrix from Germany for less than 100€, disassembled the entire central tunnel and replaced it.

No leaks around the AC site, but the old heater matrix was almost 100% blocked. After cleaning it I tried to blow inside but only very little air was coming out. Compared to the new it was day and night.

Reassembled everything, refilled the lost coolant, reset all the errors.

Aircon works again, even hotter than before. After another small trip of 1000 km coolant level seems to be stable. Will keep an eye on it in the next weeks.

 

[Honest Mate]

Update for whoever finds this thread in future.

Apparently my expansion tank is a different revision and has no physical silica bag inside. So no burst silica bag. Also checked with VCDS for errors but aircon unit had no faults.

I ordered an original Valeo heater matrix from Germany for less than 100€, disassembled the entire central tunnel and replaced it.

No leaks around the AC site, but the old heater matrix was almost 100% blocked. After cleaning it I tried to blow inside but only very little air was coming out. Compared to the new it was day and night.

Reassembled everything, refilled the lost coolant, reset all the errors.

Aircon works again, even hotter than before. After another small trip of 1000 km coolant level seems to be stable. Will keep an eye on it in the next weeks.

I will be doing this replacement but I will leave it for spring, when will be warmer outside heh.
But the colant will not leak if you would drive up to 70mph.. As soon as you will drive fast and above 70mph, you will start loosing coolant as it creates greater pressure, and if the whole circulation system is blocked in certain place the flow increasing speed is blocked so pressure can't hold and will spew coolant from tank reservoir overflow holes to prevent explodig..
Even if you drive too fast with an A3 tdi 180 or tuned you will stard burning oil.. so oil level will drop too ..
So if you replaced it and working flalwesly, try to do test with for example 100mph driving and see if you will loose any coolant.
Good thing is to even check or replace Auxiliary Water Coolant Pump.
Thanks..

 

[serrobert]

Thanks for the tip. During my last trip I only went up to highway limit (93 mph / 150 kmh). I fully understand what you mean: in fact with the old heater matrix I'd get a lot of spillage especially after highway trips. I'll keep an eye on it now that the heater matrix has been replaced.

 

[neiller]

Thanks for the tip. During my last trip I only went up to highway limit (93 mph / 150 kmh). I fully understand what you mean: in fact with the old heater matrix I'd get a lot of spillage especially after highway trips. I'll keep an eye on it now that the heater matrix has been replaced.

I have the same problem on my S3 except I don't seem to be losing coolant I just don't have enough heat from the heater when I compare with my girlfriends A3 2.0 TDi