Golf GTD Coolant Foam: Causes & Fixes

"Die Sonne scheint hell, und die Vögel zwitschern fröhlich. Ein leichter Wind weht durch die Bäume, und die Blätter rascheln leise. Es ist ein wunderschöner Tag, um draußen zu sein."

Hello everyone,

My VW Golf is giving me trouble!!!
Yesterday evening, I drove about 50 km on the highway, quite quickly. Approximately halfway, the creature emitted a peculiar sound .
The noise (audible) occurs in the low-pressure range starting at 0.9 bar. It's a moderately loud "air escaping" sound. My initial thought was somewhere in the low-pressure cooling system. But that's not the case. The boost pressure is fully present (as indicated on the boost gauge). My second thought was a crack in the exhaust or downpipe. However, I don't think that's it, because you should at least be able to hear a crack or small hole, even in the non-boosted range, and the boost pressure would increase, even if only slightly. When the hood is open, you can't hear anything because 1. the engine is loud, and 2. there's no load and therefore little boost pressure.
I thought, well, whatever, the boost pressure is there, who cares?
I got home without any problems.

This morning, I started the engine three times (-5 degrees Celsius, 100 miles on odometer), and it started normally after 2 seconds as usual. After driving less than 50 meters, the coolant warning light started flashing. Since I did the odometer conversion (and also replaced the head gasket), I haven't had to top up the coolant. My first thought was that maybe it's due to the cold, which is causing the low level. I went home and checked, and the expansion tank was empty.
I still had half a liter left, so I poured it in. About 5 kilometers later, the warning light came on again. I checked everything for leaks, but I couldn't find anything. I replaced the coolant reservoir cap, as it was faulty on the previous owner's car, and topped up the coolant.

Okay, here's the translation:

"I drove about 30 km on the highway, pushing it to the limit. I opened the cap, and then a lot of stuff came out (too much pressure?)."
When opening it slowly, nothing has ever leaked out before... So, I looked inside the top, and there's foam inside. I removed the foam with a cloth, closed the lid, drove a short distance, opened the lid again, and there's foam again.

What's going on now?
Is it related to air escaping from the turbocharger? Could there be a crack in the turbocharger, allowing the overpressure from the turbocharger to enter the turbocharger's coolant lines? That would explain the foaming! The pressure in the coolant hoses with a warm engine is normal.

Klar, normal tippt man auf Kopfdichtung, aber die hab ich vor 20Tkm gewechselt und wenn der Motor nicht heiß wird hält die ewig!!! Vorgänger bei 340Tkm verkauft mit 1. Kopfdichtung. Außerdem müsste dann das Kühlwasser am Ausgleichsbehälter nach Abgasen riechen. Tut es nicht. Wenn er das KW mitverbrennt, sollte er ja auch weiß rauchen?? EbenfalUnfortunately, nothing.

Guys, what do you think? Where should I start? What seems most reasonable?

Thank you for the tips.

Best regards,
Frank.

Hello.

Either you have a problem with the cylinder head gasket (ZKD) or your cylinder head (ZK) has a crack. It appears that exhaust gases are being forced into the cooling system, and the coolant is escaping through the pressure release valve on the expansion tank due to the excessive pressure. This is exacerbated by high engine speeds and/or high engine load. My AJM engine has had this problem for 50,000 km, and the coolant consumption is between 0.1 and 0.2 liters per 1000 km under normal driving conditions. You can identify this problem by the traces of G12 coolant that can be found everywhere under the coolant reservoir. Additionally, the pressure in the cooling system is too high.

Regards,

hb2000

Hello,

frankzda wrote:

Guys, what do you think? Where should I start? What seems most reasonable?

Well, that's a tricky question. I'd definitely start by checking if any of the clamps on the pressure hoses are loose, as the hissing sound usually comes from a leak. The boost pressure doesn't necessarily decrease if it's just a small leak. Sometimes, the intercooler can also be pushed sideways where the plastic side panels are attached to the actual radiator with those annoying aluminum clips. Or, it could be damage from a rodent bite on the back, which could have several possible causes.
"Regarding the foam: it's definitely a different construction site and has nothing to do with the 'Gezische' (likely a local reference). I would just keep an eye on it. If it's a crack in the cylinder head, the expansion tank will gradually turn black from the inside over time, so you have time to get it repaired until spring. If you're getting water into the oil or the combustion chambers, the head gasket is leaking, and I wouldn't put off fixing that, as it could lead to further damage."
By the way: If you open the cap after driving at full throttle for 30 km, it's normal for water to spurt out and for it to foam. This continues to boil further down in the hot engine as soon as you release the pressure. The bubbles rapidly increase the volume, which means a large amount of liquid is forced out quickly. Therefore, it's advisable to let the engine cool down a bit before opening the cap. In the beginning, I accidentally triggered the flashing temperature warning light on my scooter a few times and thought I urgently needed to add water. When I opened it, a lot of liquid spurted out, which I then had to refill. Ultimately, it was just the pressure sensor in the instrument panel that was broken. The head gasket in my scooter lasted 492,000 km until a crack in the coolant system caused it to fail.

Best regards, Uli.

@hb2000

"Exactly my words." -) You can test this by releasing pressure from the expansion tank (with the engine warm). Then, drive 5 km with a lot of acceleration, stop, and try to squeeze the water hoses. If there's a lot of pressure and the tank makes a loud hissing sound when you open it, then you likely have a cylinder head (gasket) problem.