Coolant Leak Through Heater in VW Polo 9N

Hello,

"When driving or turning on the ventilation in my wife's 9N (without air conditioning), there is a regular, initial smell of coolant (like Maggi seasoning) coming from the vents. Correspondingly, the coolant level has been slowly decreasing over several months."
The smell of maggots persists even when ventilating in "cold" mode.
"Bleeding" the cooling system is probably not very helpful, because even after opening the pressure release valve, excess pressure continues to escape for what feels like hours, as long as the engine still has residual heat."

Last weekend, I opened the ventilation box as far as it would go so that I could inspect the heat exchanger; it appeared to be completely dry and showed no signs of evaporated coolant.
I was also unable to detect any traces of leaks on the pipe flange connected to the engine compartment side of the WT, even without opening the connection.
Once reassembled, the game continues: after a cold start, the initial rush of wind or ventilation often brings a slight smell of maggot into the interior.

Samples taken with the hood open (in case the smell was coming from the engine compartment and somehow making its way towards the ventilation inlet) have not yielded any results so far.

Where could this stupid leak be hiding?

Hello Ulf,

UV leak detection dye in the coolant?

Best regards, Rainer.

Hello Rainer,

I'm more familiar with UV leak detection fluids being used for air conditioning systems, but I haven't heard of them being used for coolant applications.

However, based on this information, you're most likely to find a potential leak in your current stage. I know of some leaks that occur between the heat transfer fluid and the connection flange, but those were very visible, and the subjects experiencing them were already further along than you are.

matthiasTDI96 wrote:

I know of a few leaks between the heat exchanger and the connection flange, but you could see them very clearly; the subjects were already further along than you.

Aha... and which parts were installed to seal the leak?

The entire heater heat exchanger has a flange that is pressed in, similar to the coolant reservoir. However, I must admit that this was on older models (Golf 2 and 3 35i...).

OK, thank you.
Right now, I'm torn between replacing the water pump as a precaution and using a leak detection method.
Can you name a fluid that is approved by VAG for use in red coolant?
Because if this stuff, along with the coolant, for example, eventually punctures the timing chain cover , we would have really messed things up.

No, I can't do that, but I will ask the person who did it back then. Let's see if they remember... find out!

Quote:

Now I'm hesitating between replacing the water pump (WT) based on suspicion, and using the leak detection method.

Alternatively (if you don't want to use any chemicals), you could bypass the heat exchanger by disconnecting it or bridging the coolant lines with a tube.

If the smell disappears after a few days, you know something's up.

"...and it saved weight... the colleague doesn't remember, but it was also a 35i nearing the end of its life. He definitely didn't give much thought to that stuff."

matthiasTDI96 wrote:

...and you've saved weight...

*grin*
But the Polo is now considered a car for women, so it doesn't really matter anymore if it weighs 100 grams more or less.

Quote:

. The colleague doesn't remember, but he also had a 35i in the final stages. He probably didn't give it any thought

. OK... even if I were to do the test, nothing else would likely come out except for a small leak somewhere on the WT.
So, the Polo is getting a new gearbox soon, and that's it.

"Or have I overlooked the possibility of leaks in other components that are not related to the water tank (WT)? As far as I know, the water tank only contains two aluminum tubes with sealing rings and screw flange fixings."

We had the same problem with our then-current 2004 ATD Ibiza, but since I didn't detect any coolant loss (probably due to it being minor), nothing was done about it.

Just discovered: Condensation inside the lid of the Polo's coolant reservoir!

My BUK is completely dry in comparison, even though I've removed the cap on both of them when the engine was still warm, and some pressure (and water vapor) escaped.

If a head gasket failure hasn't been diagnosed in a Polo yet, it could be due to a too-low opening pressure of the thermostat valve (it doesn't seem to be constantly leaking, because even hours after being turned off, there's still a hissing sound when it opens).
"Question: What are the approximate chances of solving a mysterious water leak by simply replacing the lid?"

Can you swap the lids around?

Hutfahrer wrote:

Can you swap the lids around?

I could try that sometime.
But first, I want to let my better half drive the Polo for a few more days and see if the water starts accumulating in the cap again.

Please refer to the post by "Hutfahrer."

Quote:

What are the approximate chances of fixing a mysterious water leak with a new lid?

I would estimate it at 0%. Possibly, it might bring about a so-called improvement for a certain period of time.
Perhaps you should compare the pressures in both vehicles. In any case, the system must be depressurized when it's cold.