Polo 6C EA21: Coolant radiator leaking

[Le_Combattant]

Hello all,

A few weeks ago, I took advantage of the good weather to give the engine bay a good clean – it had really built up
all the grime from the winter.
A good clean never does any harm, and it’s always nicer to work on a clean engine.

That’s when I noticed that my coolant level had dropped quite a bit (I rarely top it up).
I added almost half a litre of G12evo.

Out of curiosity, I checked the level again (though far from following best practice)

- Slight incline
- Engine with a coolant temperature of almost 90°C (short journey)

To avoid skewing the reading, I opened the cap to release the pressure.
The level rose, but I’m still between the max and min marks, so there’s definitely a leak somewhere.

Three suspects:

-Water pump (original: 12 years/208,700 km)
-Intercooler
-Oil cooler
-Radiators
-Head gasket

Note that the fluid is still pink; its colour hasn’t changed.

This afternoon, after pressurising the system, fluid started leaking out from beneath the bumper. Using a torch, I noticed it was coming from the radiator/heat exchanger area… Great.

There’s a 99% chance it’s the intercooler radiator. It’s just behind the bumper grille, which has a gaping opening...
And that made me realise that, 10,000 km earlier, during the last oil change, the front of the gearbox (which is just behind the radiator) was greasy/damp. I’d tried to find the source of the fluid (which didn’t smell of gearbox or engine oil, let alone brake fluid).
So it was nothing other than coolant.

At 12 years old and nearly 210,000 km, it’s going to give me a right headache...

EDIT: after putting the car on ramp and cheking under het (hehe)

I found this:

PXL_20260420_124323957.RAW-01.jpg (2.75 MiB) Viewed 2790 times

We are under the car (what a surprise) and this is the pipe of the main radiator

2.jpg (2.78 MiB) Viewed 2790 times

And I found, on the main radiator, the jonction between the plastic housing and the metal disipator quite "wet". Underpressure (over 1.5bar) no leaks but still, last time I did the test, I saw drops.

[ciclo]

A small, persistent leak is visible due to residue left after drying. It doesn't seem serious.
Once located, it should be thoroughly cleaned to determine the exact source of the leak.
Hopefully, it might be coming from that large pipe.

[Le_Combattant]

A small, persistent leak is visible due to residue left after drying. It doesn't seem serious.
Once located, it should be thoroughly cleaned to determine the exact source of the leak.
Hopefully, it might be coming from that large pipe.

I will not be that confident.

During the last oil change, the gearbox (front side) was wet.
The large pipe is dry, but the metal/plastic frame is wet.

[ciclo]

You may need to use a contrast UV fluorescent additive/liquid/tracer and a UV flashlight to accurately locate the leak point.

[Le_Combattant]

You may need to use a contrast UV fluorescent additive/liquid/tracer and a UV flashlight to accurately locate the leak point.

I will try your advice.

Funny things, I drived for fun out in the countryside on winding roads, revving the engine hard (1h).
It's been 30 min and still, no leaks, or drops of coolant.

This car is like a 737. It's leaking but you cannot find the leak/replicate because it decided to stop

[Le_Combattant]

So after few days without any leaks, no a single drops: it's back.

After a short drive (10min) and and the car stop and parker for 10 min, I just saw (as before) a beautiful puddle of G12Evo.
Maybe 15cm by 15cm.

From the front (trough the bumper) the intercooler radiaotor is super dry, so the leak migh come from the location I take in pictures.