I want an Exp tank that clean. I wouldn't mind my whole engine bay that clean.K-SEAL or STEEL SEAL remnants from this being put into the cooling system in previous ownership. It is tenacious stuff which is what it's supposed to do. Thought I had got it out last time but no. Bought this car back in 2012 as a spares and repair car needing Cylinder Head Gasket renewed. Thoroughly flushed the cooling system and filled with 50-50 OAT A/F after the job.
All well for some months then saw some metallic particles collecting around the MAX-MIN indexes on the plastic bottle. That was some time ago and I checked the bottle again recently to see more of the stuff stuck to the insides of the Expansion Bottle. I had cleaned the original ~ now spotless ~ so carefully removed the one on the car, collecting the A/F for reuse as it was quite clear ~ then fitted the clean replacement and replaced the collected A/F.
That's better ~ see attached pictures ~ but, I wonder if more of the stuff is still lurking within the engine and will make its way up into the spotless Expansion Tank as happened now twice previously. The final picture is of the cleaned Tank after a twenty mile run. No sign of any "stuff". That's better. I will monitor.
No car of mine will have a dirty Coolant Expansion Tank ...