Coolant Leak: Workshop Can't Find It?

Hello everyone,

I have the following situation:
I drive a Volkswagen Touran 2.0 TDI Businessline with 140 horsepower (engine experts should know that it's the CFHC engine).
First registration: August 2012.
Mileage: 48,000 km.
Scheduled services completed.

This weekend, I was planning a trip, but then my car displayed a warning about low coolant levels.
My first thought was that it was damage caused by a weasel.
Since the car is quite new, I immediately called Volkswagen's service department.
Eventually, the service technician arrived with a canister of water, which we used to refill the coolant reservoir. We then drove the 5 kilometers to the nearest VW workshop. During that short drive, there was no noticeable loss of coolant. However, as a precaution, I left the car at the workshop for them to perform a pressure test.
The next workday, we got started.
I was immediately advised not to continue driving the car, as no warranty claims could be made for any potential consequential damage. Various tests were carried out, and... nothing was detected. There is no visible external leakage, the AGR cooler is in good condition, and the pressure loss of 0.1 bar is considered acceptable according to VW's central service.
I had already suspected that the workshop was deliberately carrying out these complicated procedures in order to inflate the bill, and suddenly the descriptions from the master mechanic became somewhat vague, such as: "it could happen... if it hasn't been checked for a long time..." etc.
Here's the next piece of news: After an extended test drive, the workshop itself detected a water leak and a pressure loss of 0.4 bar. However, they still can't find the source of the problem.
Who knows about this? Is it possible that I will have to bear the costs myself?
My problem is that I need a car for work-related reasons, and it's currently located 450 km away from my home. Even if it qualifies for warranty coverage, you are only entitled to a replacement car for 3 days.

Best regards,

Now it's getting even more confusing.
The workshop also occasionally noticed the water loss themselves, but I need to drive the car for a while longer in order to identify any further losses.

Hi there,
The results from the extended test drive suggest that the coolant loss is related to the engine temperature. They should have contacted headquarters again about this. The suspicion points towards issues like a blown head gasket, a crack, or a faulty heat exchanger.
Were the other tests in the workshop performed at operating temperature?
When someone is driving the vehicle for the first time after a repair, please make sure to include in the repair order that the vehicle was returned to the customer without any apparent issues, so they can continue to monitor its performance.
Under load (e.g., highway driving), the loss is likely to be most easily reproduced. Check the coolant level at short intervals to avoid damaging the engine due to a lack of coolant. Be prepared for the need to top it up, or that you may have to stop the car if the loss is significant. Do not add large amounts of cold water.
If there is a noticeable loss of power, the vehicle must be taken to the workshop for inspection due to your warranty.
Can you please determine the exact MKB and GKB codes?
hg
Herbert.

They conducted various tests according to the central office's specifications, and now the equalization tank is supposed to be sealed, and I will be driving with it for a while.

So, we drove home on the highway until the warning light started flashing, and then we had it towed by VW.
It doesn't make them any smarter, though.
Please thoroughly inspect the engine yourself from the outside. Can you smell anything when the engine is hot? Also, check the coolant level (MKB) and the gearbox oil level (GKB), as some models also cool the gearbox oil.
hg
Herbert.

Thank you for the answer.

I can only write the reviews once I have the car back.

Is it now a good idea for me to drive the car myself? Perhaps the workshop hopes to get rid of me this way if I break down somewhere else .

Best regards,

Sure, here's the translation:

"Another question:"

Under what conditions is water more likely to leak out quickly at high RPMs or slowly at low RPMs and under load?
Where I'm staying, I also have to drive 500 meters uphill with a 13% gradient to reach the parking lot.

Best regards,

Just driving in a way that allows the coolant, engine, and heat exchanger to reach their proper operating temperatures. So probably not with low-octane fuel and at 80 km/h in the highest gear.
hg
Herbert.

Drive 5 km on the highway at 180 km/h, then check [something].

The experts in this area are CFHC and NGB.

What is the acceptable level of fluctuation in the surge tank?
"Yesterday I drove 20 km. When the engine was warm, the coolant level was clearly above the maximum mark, but overnight it dropped to between the maximum and minimum marks. Today I drove 180 km. At 90 km, I checked the coolant level, and it was between the maximum and minimum marks. Then, at 180 km, the coolant level was just below the maximum mark."

Quote:

At 90 km, the water level was between the maximum and minimum marks. Then, at 180 km, the water level was just below the maximum mark.

In principle, the coolant level should be approximately the same at speeds of 90 and 180 km/h, provided that the operating conditions are identical.

It would be interesting to see the actual coolant temperatures measured with VCDS for both engine control unit (ECU) states.
Are they roughly the same? Could it possibly be due to the coolant pressure?

For example, in a healthy and properly sealed permanent magnet (PM) motor, after releasing the coolant pressure while the engine is still warm and then continuing to drive, very little coolant pressure will build up again.

It would also be interesting to know where the coolant level is when the engine has cooled down, and whether there is still any residual pressure in the cooling system if you remove the cap at that point.

After the engine has almost completely cooled down, the water level is at the minimum mark, but the red warning light hasn't come on yet.

Let's see what happens next.

Now that the expansion tank has been "sealed," I wouldn't waste any more time.
Onto the highway, pushing it to the limit until the fuel warning light starts flashing. It won't be long now. Then it's Volkswagen's turn.
hg
Herbert.

Quote:

After the expansion tank was "sealed"...

Hmm, did I miss something here?

Otherwise, as Herbert writes, sometimes you need to really crank up the heat...

The water level is getting lower and lower, but the warning light hasn't come on yet.
After approximately 400 km, the value dropped significantly from "max" to well below "min".
Subjectively perceived, the water seems to disappear during the cooling phase.

Let's see if the workshop can find anything.

Which of you knows what is considered reasonable (legally speaking) if the workshop continues to be unsuccessful?

Again, after the workshop let you drive with a "sealed" expansion tank for a test run, take it onto the highway and give it full throttle. Either the coolant deficiency will appear immediately, or later after it cools down.
The problem has already reached the manufacturer; you just need to follow their procedures and reproduce the error.
Don't dwell on "out loud" about why and when something happens. The engine is losing coolant, you have a warranty, and the manufacturer will take care of it.
hg
Herbert.