8.1 Cooling system flush questions

Hi there, thanks in advance for reading...

I took my new (to me ) '06 340DA out on New Years (water was cold) and once under load, my port engine started overheating. I shut it down at 203° to avoid damaging anything. Long story short, I discovered that the fresh water cooling system had chunks of material around the thermostat from the PO's attempt to fix a leak with a stop-leak product. He ended up replacing the heat exchangers on both engines before selling it to me but there's still residual gunk in the system. I've flushed it with water and a radiator flush & fill kit but there's still crusty stuff stuck to the areas I can reach with my fingers. Temps are now back to normal (155°) under load so I'm happy about that but I'd really like to get this crusty stuff out of my cooling system.

Does anyone have a recommendation of a product to use that will break this stuff down without damaging the seals, hoses etc?

Thanks again,
Brian

 

I did that to drain the block but this stuff is crusted on. It softens when wet but still sticks around. Need a chemical that I can flush through that will break this up without damaging seals and hoses.

 

I guess that's possible. I'd really like to figure out what chemical to run through the system that won't damage anything. Thanks for the interest thus far.