Copper radiators + Colour based Coolants.
Mayhems have been looking into a reported issue about the Red based coolants changing colour (Red to Dark Red and Black to Brown). This is a very rare issue but has been narrowed down a certain type of radiator.
When testing we found that just adding water and leaving overnight will turn the water Acidic meaning that either the rads have not been flush or somehow there is still acid left in the system. When acid is left on copper and air is introduced (in particular oxygen) it will create Copper Oxide over time. Copper Oxide is Blue / Green and this has a negative effect on colour coolants and will also have a negative effect on all coolants over time. (in the picture you can see a rad that has been not been cleaned turning the red coolant a deeper colour)
So say a Red coolant exposed to Copper Oxide it will start turning Dark Red (Red + Blue / Green = Dark Red). If Black is exposed Copper oxide it will turn Brown (Purple + Yellow + Copper Oxide = Brown)
It is imperative that rads are flushed properly and before use. If air is somehow trapped in a rad and the liquid is somehow acidic then once again copper oxide is created and again it will affect any coolants in the system. Some coolants do not react well with copper oxide and could over a period of time have an issue.
If somehow air is trapped in your rad end tank and the liquid is acidic once again it will produce copper oxide and once again this will affect any coolants in your system. Always make sure you remove all air out of you system and bleed them correctly.
Always flush your system fully and correctly and sometimes water alone does not do it. If you are going to acid clean your system using vinegar then you must neutralize that acid afterwards. You can use bicarbonate of soda to help do this or head down to your local aquarium shop and ask for animal safe products to bring the PH level back into neutral.
Also on a side note never add Copper Sulfate Biocide to Pastel as again the above will happen and if you have used copper sulfate in your system before using red pastel make sure you flush it out correctly.