Kühlwasserverlust bei A6 2,5 TDI :( | Posts 16+

If there's still pressure the next morning, even though you opened the cap before the trip, it must be coming from somewhere. It can only be the head gasket. If water had boiled somewhere, the pressure would have dissipated. I've never had a problem with bleeding the system in any car: with a warm engine, the thermostat open, and a high RPM, it always resolves itself.

Okay, so I was messing around with the car again today. I noticed that when I let the car warm up normally, not much happens. But if I briefly rev the engine and then let off the gas, the coolant level drops slightly (when I give it gas), and as soon as the RPMs drop, the reservoir overflows massively! It gurgles out really violently. This goes on for a long time until I turn the car off, or until a lot of coolant is missing. And even then, you can still hear it gurgling. If I refill it, the same thing happens again.

That sounds like a really good piece of poetry.

But now, here's the thing:
If the water level starts to rise, and I bypass the fan with a cable so that it runs at its highest speed, the water level automatically drops again! Even when accelerating, I could hardly manage to get the water to overflow.


What on earth is going on?

All tests were conducted with the container open!

What does the coolant temperature reading say? Is the displayed value reliable?

The gauge isn't even in the middle; it should be around 90 degrees (at the center position). I trust the gauge's reading. Compared to it, I see the oil temperature values, and I also have the activation points of the thermostat switch for the fan.

And if you measure with a regular thermometer, maybe the sensor is faulty?

Best regards, WarLord.

The display is fine. As I said, I have the power-on values for the fan.

Today, I had the CO (carbon monoxide) test done again during the water test. The ZKD (likely referring to a specific component or reading) is fine. The fluid didn't change color.

Hello forum, it's Harti again!

I've already replaced some parts and made adjustments to my Golf, but it's not getting any better. I installed the correct coolant reservoir for the engine (it has a slightly larger capacity than the old one), and I also replaced the water pump. The three-stage fan control unit is now also installed.

But none of that helps. The problem still exists. It's incredibly frustrating. What else could it be? The most obvious cause would be air in the system, but how on earth am I supposed to get it out? There are also no bleed valves in the cooling circuit. The temperature gauge is in the normal range, and warm air is coming from the heater. The fan also turns on, and the fan after-run function is working...

What else can I do? It probably isn't the thermostat, because the radiator is getting warm, and the gauge is showing realistic readings. As mentioned before, the hoses are very firm after a drive, and there's moisture around the reservoir.

Harti wrote:

... What else can I do? It probably can't be the thermostat, because the radiator is getting warm, and the gauge shows realistic values. As mentioned above, the hoses are very firm after a drive, and it's wet around the reservoir...

Check the expansion tank cap, as well as the hoses; otherwise, replace the head gasket.

I've already replaced the valve, and the hoses are leak-proof. I also had a CO test done, and there's no CO in the water.