So i checked my coolant the other day and saw it looking rather browish. i just did a flush of all the green stuff the PO had in there. during that time the Mech (if you can call those idiots that) cleaned out a lot of brown stuff(rust??) out of the overflow tank and radiator.

I made sure to put in G-48 coolant on the advise of my in-law(more like a brother) who works on and own many BMW's. what I am guessing is the new coolant is acting like a cleaner of the other rust left in the system. so should i drain and refill the system again?

is there a chemical to fully flush out any remaining rust particles?

If the 1st change was really bad you probably have to change it again.I always do 2 flushes on everything when I purchase a new car.Some say its wastefull but everything that has fluid in it is super clean....

Make sure it's not oil that's diluting your coolant. I would check the color and condition of the oil. If the 2 are mixing you may have a head gasket problem. I dunno if the brown coolant is rust or oil.

doesn't smell like oil and i do not see any other teltale signs of a head gasket problem. I am sure its from green coolant swilling around in the system for God knows how long before I got it.