Dark Brown Sludge in Radiator PLEASE HELP! :(

Hi, Im fairly new round here but Im hoping you can help me!!

I drive a '83 1.3 4 speed mk1 golf in mars red, just done a fair bit to the appearance of the car but recently I checked my coolant level and i opened the cap to find a thick rusty coloured dark brown sludge in the radiator.
This had only started building up when I had flushed the radiator and added some new antifreeze ready for storage in winter.

Could anybody please give me some advice please and if there is a fix I can do myself.

Replies very appreciated, Thankyou!

There must be somebody with an idea!  

Its an old car.

Flush it all out again and refill with antifreeze mix. As long as it doesn't over heat or loose water all is well. Repeat flush and antifreeze refresh every 2 years.

Think if you mix different types of anitifreeze (G11 vs G12?) it can go a mucky colour.  :dontknow:

Ok pal thanks for the advice,
just worried me a little because the sludge is really thick and is more solid than liquid but hey ho!
Al just flush it a few times and see if that does it any good

If its really that bad I'd try one of the proprietary flushing additives to give it a good going through.

flush system with a hosepipe, then fill it with plain water and a cup of bio washign powder run it till it gets good n hot then switch off engine allow to cool then flush out again. repeat till water is coming out clean, then refill with water n antifreeze mix

Thanks alot guys, appreciated!