It makes me wonder whether more of that sludge is lurking around in other parts of the engine. Perhaps the cooling system would benefit from a good flush through & refill with 50:50 OAT before the new radiator gets sludge up?
I intend giving it a good reverse flush when it is next back here so that should remove any that is left. You'll have taken some more of it out with the water pump change too so it's slowly being removed and replaced.
Great photo of the gloop in a bucket Richard !
In their blurb they 'helpfully' state:
" STEEL SEAL IS NOT COMPATIBLE WITH All ANTIFREEZE FORMULATIONS
Therefore, for best results, coolant should be temporarily drained and replaced with fresh water. Once repaired, drain Steel Seal from the cooling system and replace with 50/50 antifreeze. "
... but I expect many simply don't flush/drain first ?
Incidentally I have been rather sceptical about the/any 'advantages' of "Organic Additive Technology" for a while now
and will stick with good old glycol ......
That looks a lot like what I was getting in my header tank before I flushed it out more thoroughly. Interesting to see it in a worse state.
If it helps, this is a handy site for bmw m51 diesel engine parts. Just select a 5 series 525tds and year should bring up parts.
http://bmwfans.info/parts-catalog
Or this 3 series
http://bmwfans.info/parts-catalog/E36-Sedan/Europe/325tds-M51/R-A/jun1996/browse/