Coolant Leak: Audi Problems - No Faults Found

Hello,
I am completely overwhelmed.
I constantly have coolant loss. It's more when I'm driving at high speed on the highway than when I'm driving slowly. The temperature is at 90 degrees, and the oil is below 100 degrees Celsius. It seems to be dripping from the expansion tank. You can see G12 coolant splatters on the oil filter and in the underbody pan. There's no oil in the coolant, no coolant in the oil, no loss of power, and no smoke from the exhaust. All the hoses are tight, and nothing is bubbling out of the expansion tank when the car is stationary. At first, it seemed like the valve in the cap was broken. I replaced the cap, but the loss continues. I replaced the expansion tank, but the loss is still there! Over a distance of about 100 km, I lose at least half a liter (from maximum to minimum on the expansion tank). When driving at a brisk pace over the same distance, I lose about half the coolant. When driving at around 100 km/h, I lose less.

I've now been to three different Audi workshops and also to ATU, but nothing is improving, and they don't know what else to do. Also, there's no indication of a blown head gasket. And to replace it just based on suspicion (and then also replace the timing belt and water pump while everything is already disassembled) would cost at least 700 Euros!

I don't know what else to do; I depend on the car for my job and typically drive about 1000 km per week.
So far, the Audi has been extremely reliable, technically sound, and has been regularly serviced with oil changes.
Thank you for your help.
Best regards,
Micha

Audi A4 Avant 1.9 TDI, year 1998, approximately 150,000 km.

Hello,

What engine code are you referring to?

The engine code is AFN 512 602.

greetings, Micha.

Hello,

That reminds me of something:



Kühlmittel im Motorsteuergerät. Oin the email inbox.

This can be caused by the following:
Coolant level sensor in the coolant reservoir is leaking.
2. Coolant temperature sensor G62 is leaking.

This can allow coolant to enter the engine control unit (ECU) via the engine wiring harness (wicking effect).



Coolant leak at the coolant reservoir.

Hose connection, vent hose - expansion tank not functioning correctly.
The connector housing for the coolant sensor on the expansion tank is leaking.
Due to a manufacturing defect, the mesh inside the coolant hose is loose. As a result, the coolant leaks out through the vent hose connection to the expansion tank due to capillary action.



Leaks at the glow plugs on the coolant flange.

Hello,

Quote:

Nothing is bubbling out of the expansion tank when the engine is idling

.
Try doing the following:
- Disconnect the small return hose located at the top of the expansion tank.
- Unscrew the lid.
- Aim the hose into the expansion tank.
- Start the engine.

A stream of coolant must now flow from the hose into the expansion tank.

- now let an assistant really give it full throttle and let the engine run for about 20 seconds above 3500 RPM.

If the coolant stream is now interrupted by small air bubbles, then everything is clear -> head gasket failure.

Best regards, Rainer.

I find it almost unbelievable that a competent workshop wouldn't find that.

I suspect you're not experiencing any loss because a diesel engine idling produces very little heat, and therefore generates little pressure in the cooling system. However, a competent workshop should have a special cap for the expansion tank that allows you to connect compressed air to the system. They should also have an additive that acts as a strong ultraviolet dye. Add a few milliliters of this to the expansion tank, let the engine run for a while to mix it in, then apply 1 bar of pressure to the system with compressed air – or simply take a drive on the highway. Then, use an ultraviolet lamp to search for the leak.

-Uwe-

Uwe@Ross-Tech wrote:

Then, use an ultraviolet lamp to find the leak.

... and if it was the oil cooler, as it was in my case, then the oil looks like a Christmas tree. I can only confirm what UWE said.

Hello,

The symptoms sound familiar (1997 AFN A4). In my case, it was the head gasket. Additionally, I initially heard slight hissing and gurgling noises from the heater, especially when starting the engine, and later also while idling at a traffic light.

I still hope that things are different for you.

Regards,
Thomas.

Now, the car was at the VW/Audi dealership for 2 days, and they checked everything. In the end, it turned out to be the timing chain tensioner. Well, it costs 450 euros! I bought the car last year in December, so shouldn't the dealer be responsible under the warranty? The extended warranty does not cover any seal damage.
Thank you, Micha.