Series 3 Series 3 Diesel coolant going green

I flushed (using a garden hose) and refilled the coolant on my S3 diesel a few weeks before Christmas. It has been in a garage since then.

I used 40% Granville Sub Zero glycol-based coolant with de-ionised water. This says on the bottle that it is suitable for Ferrous engines. I have also read that the blue glycol types are suitable for brass radiators and heaters as fitted to the Series.

I had to drain the coolant out again today to replace one of the hoses as the old one hadn't sealed properly when I re-fitted it last time.

As my engine has a drain tap fitted, I drained it into an empty de-ionised water bottle to re-use it once the hose was replaced. I noticed that the liquid had turned from blue to green. What might have caused this? I hope there isn't any kind of corrosion happening in there. The engine was professionally reconditioned three years ago, with the disassembled block's water jacket steam cleaned inside as part of the job.

Thanks for any replies.

Google this subject and you will see loads of people wondering at this strange phenomenon. You are not alone...
You will also be scratching your head still because no one seems to know what is causing it and contradictions are rife.
My suggestion is that you don't worry about it too much, if the coolant is as fresh as you say it must still be effective. You would be best to back-flush the whole system again by a hose into the bottom hose and let it run until the water is clean. Whether you use the same coolant again is up to you. I think I would use new stuff and if it turns green as well then you can safely use the old stuff for top-ups.
Edit: Don't forget to empty and wash out the expansion bottle.

it always does- don't worry, if you filter it , you may reuse it.

Thanks for the replies.

I didn't see the point in using fresh coolant this as I had refilled it with new fluids last month and it had hardly moved since. I did flush in both directions and wash out the expansion bottle when I did the coolant flush the first time.

I know someone with a Mitsubishi Shogun 2.5TD. This also has a cast iron block with a brass radiator, they use the same Granville coolant and apparently it stays blue.

ciderman: How would you go about filtering the coolant?

I would stretch a stocking over the funnel when I poured it back into the cooling system.
Tip; give the stocking a rinse before you put it back in your wife's stocking drawer