Is 'soot' in the coolant................

................invariably a symptom of blown head gasket(s)?

Not necessarily ... Does said "soot" appear to be floating at the top of the tank, or at the bottom of it?

Top and clinging to the u/s of radiator cap.

Is she losing coolant?

A little but I've only just refitted the repaired radiator and it usually takes a week or so of use before the coolant level settles down, even after raising the front end, etc.

Slight but spotted it first when removing radiator so flushed out engine block with low pressure fresh water hose - radiator repaired and refitted, new coolant but 'soot' clinging to cap after only one day's use.

Didn't flush radiator after repair and before fitting, though, but doubt whether external 'soldered' core repair and paint respray would cause such classic symptoms.

Tour Water pump impeller is rubbing against The Water pump cover,and The 'soot' is plastic and aluminium from The Water pump.Happend to me twice

Thanks for that but just replaced water pump shaft, bearings and seals.

Risks?

I just flushed my coolant on my bike since I had a water pump gasket leak and it was low and obviously dirty, but when i drained it this is what i got. It was very dark and murky and seemed to have a slight grit floating around in it. I flushed the whole system out with a hose and plan to re flush in a few weeks. Is this like what you found?

one easy way know ij its a head gasket take radiator cap of run bike to normal temp , as it comes up to temperature it over flow so have a bucket now wait to the fan comes on now look closley at fluid if u get bubbles head gasket gone hope that helps or get what we use in the workshop leak down tester cheers bazz

I had Just replaced impeller and shaft + seal too.
But The recess on The New shaft is slightly longer than The one i replaced,i did not notice that.... Twice

From half filled, just filled the overflow tank and dumped a quarter of it through the external breather pipe, sucked a quarter back into the radiator leaving the overflow tank back at half full, a minute or so after switching off a hot engine so I'm guessing the radiator is over-pressuring...............................

Have hot-wired the fan to treat symptoms only and ordered yet another waterpump kit, just in case.

No further significant coolant loss and no more 'soot' on u/s of radiator cap - thinking that it just might be unrelated brazing residue and air pocket burb - hopefully - will overhaul waterpump again, though, just in case.