Time to replace the head gasket.
Mineral sludge from tap water. A good radiator flushing will help and then use proper coolant to help keep the sludge building up and blocking the radiator.
Time to replace the head gasket.
You can use plain water to get sludge out of your car radiator. You can use Marvel Mystery oil to remove sludge from the oil pan.
the so called sludge is most likely some sort of cooling system sealant.
Car radiator flush sold as most automotive shops
Get one of those flush kits from an auto parts store.
No You don't Need to change the water pump But you should change it and the thermostat if radiator was full of sludge. if not then no to both.
leak calicium or other deposits plugging or restricting water passages exteriors fins rotted what does sludge mean in my radiator?
Sign of possible head gasket failure
Engine oil is mixing in probably due to a faulty head gasket.
I don't know for sure, but can't you just get a radiator flush kit to get out the sludge? It's worth asking the guy at the parts house about. In such extreme cases of cooling system sludge build up, I would take it to a shop for a professional flushing and cleansing. I would suggest a car radiator specialist type shop - they'll know how to NOT cause more damage to the system. See "Related Questions" below for more about flushing it yourself
Yes, stop leak turns into a thick substance to plug any leaks, when it ends up in the overflow bottle it turns into sludge there.