Kühlwasser wird warm, Innenraum nicht | Posts 16+

'The other day, when I arrived at work (outside temperature was 0°C, driving distance was 22 km, the coolant temperature gauge showed 90°C), and the inside temperature was only 13°C (channel 56) - brrrrr! So, I opened the hood and felt the hoses connected to/from the heater radiator. The inlet hose was only lukewarm. The outlet hose, of course, was even colder.'
Then I quickly squeezed the inlet hose several times, and sure enough, it immediately became very hot, and the inside got warmer right away.
My explanation: The pressure fluctuation caused by squeezing it must have dislodged some kind of blockage, allowing the radiator to be flushed with coolant again afterwards.
Unfortunately, it didn't last long. But the trick of squeezing always works.
I bought a radiator flush today (€4.50) and I'm going to flush the cooling system.

...Sorry, but to me, that sounds more like an air bubble or simply air in the system.

The heater hoses are very thick, and you definitely can't build up that much pressure by squeezing them; your water pump already provides that amount of pressure.
It sounds much more like there's an air bubble in the system.
A blockage caused by a foreign object is also less likely, as you would only be able to remove it by pushing the tube if the blockage were located directly within that tube or immediately in front of or behind it.

How did you bleed your system, and are you sure all the air is out?

I've encountered a similar problem with an older vehicle before. However, I was able to bleed the system by keeping it open and adding water while the engine was cold. After the warm-up phase, the coolant level remained the same. Then, I had to turn up the heating system regulator and completely overfill the system until the air bubble finally escaped.Then I drained it back down to the normal operating level.

...Sorry, but to me, that sounds more like an air bubble or simply air in the system.

It sounds much more like there's an air bubble in the system.
A blockage caused by a foreign object is also less likely, as you would only be able to remove it by pushing the tube if the blockage were located directly within that tube or immediately in front of or behind it.

How did you bleed your system, and are you sure all the air is out?


Well, with the engine running and the heater turned on, I opened the bleed valve in the coolant reservoir behind the heating valve (the black plastic screw). And only coolant came out. That's why I assumed that the system was completely bled.
That's quite a high position, after all...

...it is indeed reasonable to assume that the system is then completely vented.
I assume you've checked this repeatedly, as the air bubble might also work its way through later and only then be released through the vent valve.

Well... maybe there's something to your constipation theory, but I still kind of doubt it, and unfortunately, I don't have any other advice.

Quote:

Tja, ich habe beim warmen Motor und aufgedrehter Heizung das Entlüftungsventil im Wasserkasten hinter dem Heizungsventil (schwarze Plastikschraube) aufgedreht.

And are you sure the thermostat was already open at that point?
For me, when it comes to the engine running "warm," it means that the radiator fan turns on for the second time.

Yes, I'm sure. However, it's not entirely easy to get the TDI to a point where the thermostat opens. But I've confirmed that the *lower* thick hose leading to the radiator, which is located far away from the engine block, has become warm.

Hi,
As far as I recall from the documentation for the climate control diagnosis, it is possible to query the position of the actuators, but not to actively influence them.


Hi Olli, I accidentally figured it out. You can actually influence them after all. Check this out:
Okay, I'm ready. Please provide the German text you want me to translate into English. I will only give you the translation.

Hi,
Indeed, outside of the summer months, it's difficult to get a TDI engine properly warm in the yard. A warm hose isn't enough; the radiator itself also needs to be sufficiently warm.
However, when I installed my auxiliary heater, I only pre-filled the hoses leading to the heating unit slightly. Any remaining air had to pass through the heat exchanger. I didn't open the bleed valve. I just briefly ran the engine at 2000 RPM while it was stationary.
From my perspective, your problem seems a bit more serious. After all, our vehicles are quite similar, except for the manual air conditioning in mine.
How does the water flow when the heating valve is closed? Is there a pressure relief valve? I haven't heard of that before. Or is the necessary pressure difference created by a specific throttling point in the cylinder head, which forces the water, or part of it, through the heat exchanger?
The pressure wave you created by squeezing the hoses could just as easily have moved a foreign object inside the cylinder head.
So, the best way is to flush all the parts with alternating flow directions and sufficient pressure.

Hello,

Yesterday, I finally tackled the issue.
Ich habe den Schlauch vom Zylinderkopf zum Wärmetauscher und den Schlauch vom Wärmetauscher zum Motorblock abgemacht und mit dem Gartenschlauch durch den Motorblock gespült: alles astrein, in beiden Richtungen. Dann habe ich den Wärmetauscher gespült: es baute sich ein hoher Gegendruck auf und am anderen Ende kam eine fiese, trübe, braune Suppe heraus. Ich habe dann lange immer abwechselnd in beiden Richtungen den Wärmetauscher durchgespült, bis nur noch klares Wasser an der anderen Seite herauskam. Allerdings blieb der recht hohe Gegendruck (im Vergleich zum Spülen des Motors). Das Heizungsventil ist ja offen, wenn kein Unterdruck anliegt. Ich weiß nicht, ob sich irgendwo im Schlauch noch eine Drossel befindet. JI will definitely have a radiator flush done.I poured it in and drove about 50 km under higher load with higher RPMs. During that time, I had the heater on HI. So what? When the interior temperature reached 29°C, I turned the heater down . Then, I flushed it again with water and refilled the old coolant without the sediment.
Now it's not cold inside anymore, but I still wonder why the water flows so poorly through the heat exchanger. Maybe it's still completely clogged, only the dirt hasn't been completely flushed out . Replacing the heat exchanger is something I can do without right now; that would probably be a bigger job.

Does anyone have a better method for flushing the heat exchanger than using cold tap water? What pressure can the heat exchanger withstand? Could you perhaps use a high-pressure washer to flush it out? Or could you put dishwashing detergent in while rinsing? How much does it cost to replace the heat exchanger at a workshop?

Hi,
It won't withstand much pressure: The valve in the cap of the expansion tank opens at 1.2 or 1.3 bar. A safety factor of 2 would mean a maximum pressure of 2.5 bar.
Anything that goes beyond a certain level becomes gambling.
I wouldn't attack it too aggressively right now, so no harsh chemicals. If there's not just rust sludge from the crankcase or radiator sealant inside, but also aluminum corrosion, which you might not know beforehand, the risk of it leaking is too high.
During the time it takes to replace one part, others are almost completely replacing an entire engine.
Fresh coolant would be a good idea.

Am letzten Wochenende habe ich mir mal einen Gartenschlauch genommen und jeweils ein Stück am Wasserauslass des Motors für den Heizungswärmetauscher und dem Wasserrücklauf aus dem Heizungswärmetauscher in den Motor angeschlossen. Beide Enden habe ich in einen Eimer mit Wasser gehalten. Den Eimer habe ich vor dem Auto etwa auf dem Niveau des Motors gehalten. Na uSure, here is the translation of the text from German to English:

'nd?'

This could be a shortened version of 'und?', which means 'and?'. It could also be a typo or an abbreviation for something else. Without more context, it's difficult to say for sure what it means.

Diagnosis:
'Almost no water came out; only a thin stream of about 3 mm in diameter. At higher speeds (helper), it was slightly more. Of course, this means very little heat can be transferred (P = dm/dT * (Tein-Taus)). This also explains why the heating system only works somewhat at higher speeds and hardly functions at idle. Since the fan speed is apparently determined solely by the supply temperature, the climate control system always turned the fan up high, but only blew cold air, even though 90°C was displayed in channel 51, and the temperature air flap (channel 8 or 10) was closed, meaning all the air was being directed through the heater core.'
Repair:
'I've flushed the system again. I could have saved myself the expensive VAG coolant (33 euros for 5 liters), as it only consists of ethylene glycol (coolant) and 10% citric acid. The latter can be bought cheaply at a pharmacy (it's a white powder that looks like sugar) and is an excellent limescale remover, and it doesn't smell nearly as bad as vinegar -> household.'2. On the thermostat, I bent the small round metal plate so that it partially blocks the opening for the return of water from the engine block, even when the thermostat is still closed. This slightly increases the pressure in the water flow and improves the circulation through the heating heat exchanger.

Result:
Finally! The heating is working again. Even with a displayed pre-temperature of 50°C, a warm airflow enters the interior, and the car warms up much faster.

Sure, here is the translation of the text from German to English:

'Addendum:'

Ich habe mir von einer Standheizung eine elektrische Wasserpumpe besorgt, die will ich in den Heizungskühler-Kreislauf einschleifen und zusammen mit dem Signal für das Warmwasserventil einschalten lassen. Davon verspreche ich mir noch bessere Heizleistung. Oft steht man im Winter bei langsamen Drehzahlen (kleiner Volumenstrom) und langsamen Geschwindigkeiten (wenig Abwärme) in der Stadt 'rum. DA higher flow rate should at least help.

But right now, things seem to be pointing towards a cooling off period. Let's see when I find the time for it...

Addendum:

Ich habe mir von einer Standheizung eine elektrische Wasserpumpe besorgt, die will ich in den Heizungskühler-Kreislauf einschleifen und zusammen mit dem Signal für das Warmwasserventil einschalten lassen. Davon verspreche ich mir noch bessere Heizleistung. Oft steht man im Winter bei langsamen Drehzahlen (kleiner Volumenstrom) und langsamen Geschwindigkeiten (wenig Abwärme) in der Stadt 'rum. DA higher flow rate should at least help.

But right now, things seem to be pointing towards a cooling off period. Let's see when I have time for it...

So, nun ist genug Zeit vergangen und der Leidensdruck groß genug gewesen. Ich habe heute die Pumpe in den Schlauch vom Wärmetauscher zum Zylinderkopf eingebaut, das Kühlsystem entlüftet und eine kleine Probefahrt gemacht: Es war ein voller Erfolg. Q Punkt ist größer und schon bei in Kanal 51 angezeigten Temperaturen von ca. 35 ° Celsius tritt warme Luft aus. Ich bin nur ca. 2 km im Ort zur Tankstelle gefahren und zurück. Außentemperatur 2 °C. Nach It was wonderfully warm inside during the short trip!

'Now I'm going to build a small relay circuit that will draw its control current from the solenoid valve for the hot water valve. Additionally, I'll disable the hot water valve so that the heat exchanger is always flowing, even in summer. This should prevent it from becoming clogged as easily. I'll report later whether this has any impact on the cooling performance of the air conditioner.'
PS: The current mileage is approximately 315,000 kilometers.

Channel 51 in the climate control system likely displays a calculated value rather than a measured one.

To test it, turn on the ignition for 5 minutes without starting the engine. The value should also increase to 90 degrees in this case.

Best regards,
Uwe

Hi there, regarding your topic: I would advise against using a radiator cleaning additive unless it's absolutely necessary. There's a significant drawback: the water pump can be severely damaged by this type of product. Also, you mentioned that you replaced the water pump. As far as I know, there is a modified water pump available for the C4 with the 5-cylinder TDI engine. This modification significantly increases the coolant circulation rate.

Channel 51 in the climate control system probably displays a calculated value for you, not the measured one.

To test it, turn on the ignition for 5 minutes without starting the engine. The value should also increase to 90 degrees in this case.

Best regards, Uwe.

It's not quite, the value slowly increases and then plateaus at exactly 50°C. So, for a while after starting, it won't display the correct temperature until the actual temperature exceeds 50°C.