A4/B5 Heat Exchangers: No Heating Needed - Solution

Hello,

The heating system in my grandparents' A4/B5 car has stopped working.

Workshop diagnosis: Heat exchanger is blocked and needs to be replaced, cost: €480.

After that, the whole thing would likely have been back to normal in a short time, as algae were already growing in the balancing tank.

I then took on the matter.
Equipment:

Ramp, pit, or lift platform (it was just a small ramp).
3 bottles of G12++ coolant.
1 bottle of cooling system cleaner.
Thermostat.
O-ring.
Tool.

So, I first removed the underbody panel and drained the coolant (Caution: Harmful to health and requires proper disposal!).
It looked more like muddy water. Also, the bottom of the collection basin was covered with rust particles, some of which were as large as a fingernail.
Then I removed the thermostat.
After that, I reassembled everything without the thermostat and filled it with 1.5 liters of cleaner and clear water. --> Turn on the heating - for at least 20 minutes.
Everything was drained out - the liquid turned back into a slurry of pigment and rust particles.
I put the old thermostat back in and started another cleaning cycle.
Okay, I'll translate the text:

"Again, I removed everything and then unscrewed the hoses for the heat exchanger in the engine compartment. I flushed them in both directions with a garden hose (but it barely worked)."
Reassemble everything and fill it with clean water. Additionally, dissolve two dishwasher tablets in the water and run another heating cycle.
Okay, let's drain everything again. Flush the heat exchanger and refill it with dishwasher tablets. This time, also install the old thermostat. Run the system, drain it, and then flush the engine, radiator, and heat exchanger with the hose (in both directions).

Finally, install the new thermostat, reattach the underbody panel, fill the system with G12++ (mixed 1:1 with distilled water), and bleed the system.

Ready - it's heating up again.

Approximate cost: Thermostat €35, G12++ coolant €39, and cleaner €38 (enough for 3 flushes).

Interestingly, the cleaner's instructions state: "Drain the coolant, bring the engine to operating temperature, and add 1.5L of cleaner, then top off the rest with clean water..."
I definitely wouldn't pour cold cleaning fluid into a warm engine, and I wouldn't let the engine run for a long time without water... What do you think?

It was quite a job, but without a thorough cleaning, even replacing the heat exchanger won't make much difference. And the workshop definitely won't clean it with that level of effort!

In March, we'll also be doing a transmission fluid change and replacing the shock absorbers.

hello,

That's roughly what cleaning should look like! I also did it this way once during my apprenticeship.
I only used an original VW cooling system cleaner. Additionally, I replaced the expansion tank (the hoses seemed to be okay).
I once filled the heat exchanger with cleaner and let it sit for about an hour.

Unfortunately, the whole process is quite time-consuming, and that brings up the old problem:

The customer then pays xxx€ for the cleaning, and no one can tell them how long it will last.
However, impurities remain in the system, and these can clog the cooling system or the heat exchanger again, either tomorrow, in two weeks, or, with luck, not until three years from now.

Actually, one should clean and replace the WT (water pump), but unfortunately, for some A4 models, this is already close to a financial disaster.

That's true. It's very time-consuming to replace the wiper blades. And a cleaning like that at a workshop is almost prohibitively expensive.

The quote included something around 50€ for the cleaning.
It's probably not a good idea to add more than the recommended amount of cleaning solution.

Well - we'll see how it goes .

I also wanted to replace the expansion tank, but I forgot to order it.

And I'm usually in Zurich, while my grandparents are in Zittau (830km), so things have to work out like this .

The most important thing is: while rinsing with compressed air (max. 3 bar), alternately blow air through the system, then flush with hot water and air in the opposite direction of the flow until no more scale deposits come out.
If necessary, use the cleaner twice, as it may be used up during the first pass.

Hello!

Can someone explain to me why this corrosion forms in the engine block?

I often see this issue with older Renaults; they seem to be particularly prone to it.
And once that rust stain forms, you'll never be able to completely remove it.
"But with some other, seemingly identical Renault cars, this never happens..."

Steffen G wrote:

Hello! Can someone please tell me why this corrosion actually occurs in the engine block? With some completely identical Renaults, this never happens...

I once read that atmospheric oxygen promotes the decomposition process of glycol, while pure water naturally promotes the formation of scale and (together with oxygen) rust.
Then there are incompatibilities (for VAGZB: G11 and G12, G12+).
Conclusion: Some cooling systems may develop minor leaks.
Some people occasionally refill the water and continue on their way, which is good sometimes .
The others look for the cause, eliminate it, and then everything is good again.

I also had a Passat recently with a clogged catalytic converter.
Diagnosis in the workshop: Water pump is defective.
However, since I had experienced a faulty water pump myself in the past, I was able to rule it out based on the circumstances. The workshop wanted to charge the lady 700 euros for the replacement.
I then cleaned the water tank as described above.
What I noticed was the color of the coolant, which was almost purple.
I then asked the lady what she had put in the tank, and she brought me a bottle of bluish coolant from the trunk of her car, which the gas station attendant had sold her.
Apparently, this blue, surfactant-based coolant is not compatible with our G12 or glycine, which results in the formation of flakes, similar to what happens with fabric softener in a washing machine.
Okay, she paid me 20 euros.

@ Tagessuppe, exactly, but not just superficially.
General knowledge regarding VAG: in fact, G11 and G12 (+) are not mixable!

It's common knowledge that these substances are not miscible, and it's also clearly stated on the bottles and containers.
But I only learned that it specifically creates something like a paste through volunteer test subjects .

No offense, Severin, got it.
You only truly realize how bad it is by trying it yourself, even if you already know and have read about it.
However, 20 € was too cheap; 39.50 would still have been a bargain. 15.50 for materials and half an hour of work – you're selling yourself short .
It doesn't necessarily have to be 65, like it was with the friendly person .

It was a friend, and for about 20 euros, I treated myself to a Wiener Schnitzel and a beer.
But you're right. You don't get rich that way.

Update:

I found some Aral coolant (green, based on surfactants) in my grandfather's garage (and I disposed of it properly!).

And after 5 weeks, the box is still heating up well .