Leak detection guide for the cooling system

Hello,

Since the last inspection, my Passat has been leaking and is suffering from a lack of coolant . However, the leak is often difficult to locate due to the air turbulence that occurs during driving.

I then developed a simple method for finding leaks, and I wanted to share it with you (in case someone hasn't already).

Let's take:

- Bicycle pump with pressure gauge.
- a piece of fuel hose.
- Bicycle valve
- Round iron

I have now carefully removed the vent hose from the expansion tank and inserted the fuel hose there, the other end of which was plugged with the bicycle valve. I then closed the vent hose itself with the round iron. Afterwards, inflate to 1 bar (during this process, you can also verify the pressure regulation of the expansion tank) and search. In my case, the leak was immediately visible as a stream coming from the radiator .

It was interesting to observe a pressure difference between the two cooling circuits (large and small): After disconnecting the fuel hose at the expansion tank, I assumed that the cooling system would no longer be under pressure. Unfortunately, that was not the case. After removing the round metal piece, a jet of coolant came out, reaching as far as my neighbor's garden and fluctuating periodically in intensity (approximately 5 seconds). Is this normal? This pressure separation can only be caused by a closed thermostat (which opens during the inflation process until the pressure is equalized in both systems, and then closes again due to the spring force) .