AFN ZKD wieder kaputt? | Posts 32+

Hello Günter,

I didn't mean the air (the gas) that's dissolved in the water, but rather the stuff that appears as tiny bubbles floating in the water. My observation with the water heater is: as long as the water is hot, it looks milky because there are huge amounts of tiny gas bubbles in it. When the water cools down, the smallest gas bubbles disappear, and instead, you have larger air bubbles forming on the heating elements. My assumption is that the larger bubbles are formed from the smaller ones. You can hear large bubbles gurgling, but you can't hear the smallest bubbles...

Regards,
Thomas.

Okay, kettle-theory mode activated: A hot heating element causes the water in its immediate vicinity to boil. Steam bubbles form and attach to the heating element until the buoyant force overcomes the adhesive force. Then they rise, join together with others, and come to the surface.
This has little to do with the process inside the car itself, although there is certainly a possibility for it to occur in the cooling channels. However, the formation of steam bubbles in the cooling system is completely undesirable. Combustion gases that are forced into the system through the cylinder head gasket will not react with the water; instead, they follow the high volume flow and escape through the valve in the expansion tank, where they can be observed as vigorous bubbling.
It's also possible that when the engine is turned off, this gas can remain trapped in all the bends and curves of the system. That will bubble later.

Hello Günter,

I didn't mean the air (the gas) that's dissolved in the water, but rather the stuff that appears as tiny bubbles floating in the water. My observation with the water heater is: as long as the water is hot, it looks milky because there are huge amounts of tiny gas bubbles in it. When the water cools down, the smallest gas bubbles disappear, and instead, you have larger air bubbles forming on the heating elements. My assumption is that the larger bubbles are formed from the smaller ones. You can hear large bubbles gurgling, but you can't hear the smallest bubbles...

Regards,
Thomas

Hello Thomas,
What you see as small gas bubbles is gas that is dissolved in the water, and which escapes due to the decrease in solubility when heated!
You will notice significantly fewer bubbles when reheating.
However, these are 'quantities' that can never form such large air bubbles that they would 'gurgle'!
It 'gurgles' only when there is air trapped in the cooling circuit (this also applies to the hot water heating system at home).
Best regards,
Günther.

Hello Günther,

Ah, this man knows what he's talking about. That sounds plausible. So, it looks like my theory is wrong.

The sounds I called 'gurgling' are not comparable to the gurgling of a drain or a heating system. More like a quiet hiss, which sounds more like small air bubbles.

So, all that's left to do is hope that the noise goes away and the device continues to function properly.

Regards,
Thomas.

The sounds that I called 'gurgling' are not comparable to the gurgling of a drain or a heating system. More like a quiet hiss, which sounds more like small air bubbles.
Could it be the electric coolant auxiliary heater (or whatever it's called)? Which of the experts knows under what circumstances this heating system is activated?

Regards,
Stefan.

The sounds that I called 'gurgling' are not comparable to the gurgling of a drain or a heating system. More like a quiet hiss, which sounds more like small air bubbles.
Could it be the electric coolant auxiliary heater (or whatever it's called)? Which of the experts knows under what circumstances this heating system is activated?

Regards,
Stefan

Hello,
This 'glow plug heating' system is used at coolant temperatures below 50 degrees Celsius (?), and with 'sufficient' electricity, to shorten the warm-up phase and reduce emissions.
It shouldn't make any noise, as the water is only being heated, but not brought to a 'boil.' The power output is 250, 500, or 750 watts.
Best regards,
Günther.

Quote:

to shorten the warm-up phase

I believe their primary function is to allow the heating system to start up earlier, as they are installed in the line leading to the heating heat exchanger.

Hi,

People, you can also make things unnecessarily complicated. Just take a look at the technical article about GSH.

Okay, I'm ready. Please provide the German text you want me to translate.

Best regards,

Jan.

Thank you, Jan!
Alternatively, the spark plugs can be checked in a quiet environment (!!) and with the engine off by listening to them, by briefly connecting them to the battery+. The heat output of an intact candle instantly causes the surrounding water to boil, which can be heard as a hissing/bubbling sound.
If the relay, the control system, or the wiring has a defect, it could potentially lead to the effect that meyert is describing. It can be easily tested by simply disconnecting the connectors if you hear a hissing sound, or by connecting LEDs as described in the technical article.

However, that's just a guess, as we also noticed that hissing sound in our car. We tried using a stethoscope to check the glow plugs. So, it was a deliberate effect.

It shouldn't make any noise, because the water is only being heated, but not brought to a 'boil.' The power output is 250, 500, or 750 watts.
However, it does. See the technical article and our test. Of course, it doesn't boil the water throughout the entire cooling system, but only in the immediate area around the glow plug. I may have expressed myself somewhat ambiguously.


Regards,
Stefan.

Hello everyone,

The issue with the glow sticks might be an explanation for the bubbling.
750 watts is almost like a small kettle - the one in our kitchen even makes noises when it's boiling.
It would at least explain why it only happens in the winter and only after a cold start.
I wasn't aware that these things consume so much power.

If I pull the fuses while the engine is cold and then start driving, I could test the entire system.

Or will something break if the pins don't heat up?

Michael.

Sure, here's the translation:

'Addendum:'

Then something else must be broken, because there shouldn't be any boiling noises when the water is flowing freely.

Is there a valve that switches the flow from the small circuit to the large circuit?
Or is it clogged?


Michael.

Thank you, Jan!
Alternatively, the spark plugs can be checked in a quiet environment (!!) and with the engine off by listening to them, by briefly connecting them to the battery+. The heat output of an intact candle instantly causes the surrounding water to boil, which can be heard as a hissing/bubbling sound.
If the relay, the control system, or the wiring has a defect, it could potentially lead to the effect that meyert is describing. It can be easily tested by simply disconnecting the connectors if you hear a hissing sound, or by connecting LEDs as described in the technical article.

However, that's just a guess, as we also noticed that hissing sound in our car. We tried using a stethoscope to check the glow plugs. So, it was a deliberate effect.

It shouldn't make any noise, because the water is only being heated, but not brought to a 'boil.' The power output is 250, 500, or 750 watts.
However, it does. See the technical article and our test. Of course, it doesn't boil the water throughout the entire cooling system, but only in the immediate area around the glow plug. I may have expressed myself somewhat ambiguously.


Regards,
Stefan

Hello,
'The glow plug heating system is only activated when the engine is running, and then the water is circulated (in a small loop), so you don't hear anything!'
Best regards,
Günther.

Also, sometimes it's worth considering the installation location of the geothermal heat system. It's attached to the cylinder head.

Hello,
'The glow plug heating system is only activated when the engine is running, and then the water is circulated (in a small loop), so you don't hear anything!'
Yes.

(...)If the relay and/or the control unit and/or the wiring has a problem, it could potentially lead to the effect that meyert describes. (...) Even if the motor is not running.

I've had relays before (not this type), that would switch off with a delay. The voltage is switched off at the coil, and after a few seconds, the contacts finally start to open.

meyert,

Before this becomes an endless thread , could you please describe the symptoms in more detail?
Engine on/off.
Cooling water temperature.
etc.

Or simply try pulling out the connectors if you hear a hissing sound.

Regards,
Stefan.

I've had relays before (not this type), that would switch off with a delay. The voltage is switched off at the coil, and after a few seconds, the contacts finally start to open.



Regards,
Stefan

Hello Stefan,
If it's not intentionally caused by an external coating, then they are probably defective.
Best regards,
Günther.

Hello,

Of course, the heating system has started making that gurgling noise again. Whenever the engine is under load, air accumulates in the cooling system, which then gets pushed through with a gurgling sound during the next start. One day of riding the piano, and the gurgling sound is gone.

So, we checked the cylinder head bolts: all the bolts could still be tightened further with a standard 1/2-inch ratchet without much effort. I don't think that's normal. So, we initially turned all the bolts a further 90 degrees, and then gradually brought them up to 115 Nm. Based on feel, the optimal torque seemed to be around 110 Nm. At that point, the tension on the bolts felt quite even. In addition, the screws developed completely different stress behaviors.

Let's see if that rattling sound goes away now. If necessary, we would try again to complete the entire assembly process using new screws.

It's interesting to consider why the screws lost their tension. Back then, we tightened the screws to 40 Nm, then 60 Nm, and then rotated them an additional 90 degrees in two stages. Today, we found another description that mentioned rotating them another 90 degrees after the engine had warmed up. What's going on? Could it be related to this?

Regards,
Thomas and km124.