Losing water

[M4rkL]

I have an A3 8v 2013 2.0tdi, does anyone know why i i use 500ml of water but only on long journeys. I can go to work everyday and not lose a drop of water, had the car into garage and there are no leaks, had the head and cooling system pressure tested, and both ok. Any idea's 

[Stevey Y]

11 minutes ago, M4rkL said:

I have an A3 8v 2013 2.0tdi, does anyone know why i i use 500ml of water but only on long journeys. I can go to work everyday and not lose a drop of water, had the car into garage and there are no leaks, had the head and cooling system pressure tested, and both ok. Any idea's 

Hi possibly the header tank cap as the seals deteriorate with age and let by water vapour when the water temperature is high for prolonged periods.

Steve.

[M4rkL]

Hi Steve, the car temp gauge stays at normal, would the cap still leak vapour do you know, many thanks

[Stevey Y]

22 hours ago, M4rkL said:

Hi Steve, the car temp gauge stays at normal, would the cap still leak vapour do you know, many thanks

Hi yes the cap could still leak as you won't have used sufficient coolant to cause it to boil as the pressure loss is one way which is out as a fine mist I have even had it where the cap locks down and over pressurises the system and caused the thermostat housing to leak, for what a new cap is its worth trying.

Steve.

[SteTB]

Hi,

Did you replace the cap? and did this fix the problem?

Ste

[M4rkly]

On 6/30/2022 at 10:01 PM, SteTB said:

Hi,

Did you replace the cap? and did this fix the problem?

Ste

Changed the capand it didn't nothing, it worked out it was the exhaust manifold matrix causing the fault. Cost of repair was over £2500