Brown sludge in coolant header tank

[SouthernSeat]

Hope everyone had a great Christmas!

The coolant on my 2.0tsi 190 has been getting browner and browner along with it needing topping up very occasionally.

Decided to suck out the coolant in the header tank and found a load of brown sludge in the bottom.
Having topped up with fresh coolant, I ran the engine for a few mins and it unsurprisingly quickly turned brown again.

I bought the car in June 2024 and it had already had the header tank replaced for the non Silica version (according to the invoices the level switch was faulty.)

The sludge is like a fine slightly gritty paste.

I'm wondering if the silica bag burst before I bought the car, it was replaced but the coolant was flushed properly.

Can anyone confirm what the silica looks/feels like?

 

[James_R]

The general consensus is that the brown, gritty debris found in your header tank is left over casting sand that (over time), dislodges itself from the inside of the cylinder block.

It looks like another flush will be required.