Brown deposits inside radiator

[Famine]

The water in the radiator of my VR seems to be getting a bit low so I topped it up today, whilst looking in there I could see a brown buildup on the walls of the radiator, is this normal? I cant fiugure out why it keeps getting low on water, I cant even see it leaking. Ive had the manifold gasket replaced, water pump replaced, new thermostat etc, pretty much everything and the damn thing still leaks. The other night I was driving it and the water temp light came on and the needle was at 3/4 on the dash. I dont want to cook the motor

Any ideas?

 

[TheForgotten]

brown stuff is sludge from coolant pellets dissolving. not harmful at all.
as for colant level dropping, how much coolanty is there compared to water?

 

[Stupa]

with the commodores they use a higher grade of coolant than most cars, this means it is also more expensive but they are clearly marked. I have found with mine that using cheap coolant caused alot of brown muck to coat my radiator and overflow bottle and probably everything else i havent cheked. If it was me Id run a flush through and then fill up with commodore grade coolant.

 

[hako]

The brown stuff is probably rust - the engine block and head are cast iron which rusts like crazy. If previous owners used the proper coolant and the pellets then the brown deposit probably would be from the pellets but your VR is now 12 years old and has possibly been filled or topped up with water or a coolant not to Holden specs....result is rust. As the rust increases so does the possibility of the junk blocking the tubes in your radiator meaning it will not be able to cool your engine.
As Stupa says, flush and fill with proper coolant and hope that its OK then. Summer is coming!!!