If it is brown, you might have oil in the coolant, not good. Or it could be simply rust. Just the condition of the oil.

Flush the coolant and check after 20 miles.

If oil in again, most likely a head gasket.

I’d say mixed incompatible coolants as well.

I’ve seen the internals of the water pump flake off as a gold color before. Check for leaks at the weep hole or pull the belt and check for play in the pulley.

If you have a key for the van, you can insert the key and turn it on, off, on, off, on (all without actually starting it) n the codes will pop up in the odometer.

I’d say first take a line off heater core see which way the flow is take a pressure washer or good hose with great water pressure and reverse the flow flushing coolant system for about 10 to 15 mins put fresh antifreeze in it if that’s stopleak or any other sealant it’ll flush it out which will find the original issue.

If the radiator cap on the bottom is covered in sludge, it’s a head gasket issue.