Coolant Issue - Air Sucked In

[brightWYFR]

Hi all,

I have a 2015 Leon 2.0 TDI FR (150). I have not had it long, and i noticed an air gurgling swishing noise from behind the heater matrix in the car, on idle, and also when the car is switched off with ignition on, as the electric pump still circulates.

So I thought this was the dreaded heater matrix blocked issue. I have since replaced the heater matrix. The original heater matrix was not blocked, but I changed it anyway.

I also found the oil in the engine to be quite thin and transparent looking. So i gave the engine an oil and filter change also.

The air gurgling noise is still there, and I cant for the life of me work work out where this is coming from, and how the air is being drawn into the coolant system.

I am not losing any coolant, there is no oil in the coolant or any mayo-like substance in the oil (oil/water mixing), I dont notice the noise when I am driving, I am guessing this is because the engine noise drowns out this noise.
It is only obvious when the engine is switched off and the electric motor is working overtime.

When I take the coolant cap off, I can see the bubbles periodically coming to the surface and escaping.
How can the engine be sucking air in, but not forcing any water out ?

Has anyone else has this problem, or could you provide me with any pointers?

 

[SRGTD]

From what I’ve read on this forum, the Leon’s cooling system is quite complex and it can be difficult to remove all trapped air after a DIY drain and refill. Is It possible there was air trapped in the cooling system after you changed the heater matrix? If so, then it might be trapped air you can hear gurgling, rather than air being drawn into the cooling system, and the bubbles you see in the expansion tank when you remove the cap could be that air being gradually purged from the system.

 

[brightWYFR]

I have read some posts stating there are 3 different coolant circuits in the Leon . Is this true ?

Im not sure how to go about removing the airlock, do you have any suggestions ?

The air seems to be gurgling away at the firewall, im guessing where the heater matrix pipes meet the flange in the engine bay.

I could remove the hose connected to the matrix exit pipe from the engine bay and cycle the pump, to ensure the matrix is full, and then reconnect ?

Im hoping it is just air trapped in the system and not air being sucked in somehow.

 

[SRGTD]

Yes, there are three circuits. I don’t own a Leon, so not sure I can answer your questions regarding removing the air lock.

Post #47 by forum member @SuperV8 in the discussion topic at the link below does mention purging the system using a diagnostic tool (VCDS or similar), although they do say the cooling system will eventually self bleed.

Leon Heating Only Working On Passenger Side

Should it be consistent? I thought surely the bubble would just be filled out by the coolant? Does the system need to be bled and then filled up properly? Not sure about your 1.6Tdi engine, but the Cupra engines require a specific bleeding sequence with valves operated by OBD11 manually to...

www.seatcupra.net

 

[brightWYFR]

Thank you for your help. I will read through this and have a mess around with it over the weekend. That gurgling noise is driving me insane and worries me that the head gasket might be to blame. If i can eliminate this, i will be happy. Thanks again.