94 civic ex overheat issue?

-quick question. 94 Civic EX just less than 300,000 miles. Swapped out a rusted leaky radiator for my sister yesterday due to overheat issue. Fluid was brown and milky. Brand new radiator installed, system flushed. No leaks after swap. Car overheated again and radiator was filled with milky brown fluid. Radiator still leaking fluid but not externally. I suspect cracked water jackets and the fluid to be a mix of oil and antifreeze. Thoughts?Overheating and oil in coolant fluid means a blown head gasket, most likely. Or a cracked head if you are unlucky.
the problem started long before you got there, that is rusty water which is BAD because a vehicle needs antifreeze for a reason and in order for water to rust like that requires years of abuse And since this radiator probem was not fixed a lot sooner its likely now a blown head gasket. At this point check the oil if its milky or foamy park the car. In all likely hood you had an air pocket after the new radiator and flush, you need to work those out first. I flush the vehicle as best I can, fill it up, drive it for less than ten minutes and park it. Let it cool down and watch the overflow bottle. If the system is working correctly it sucks the coolant back into the radiator as it cools, getting rid of any air pockets. The radiator should be full by this time, then fill the overflow as needed and your good to go. If the radiator does not suck the coolant back into it as it cools, replace the radiator cap, they do go bad. Another thing that happens is if you did not back flush the radiator and the engine water jackets, rust builds up on the bottom, well now the system is clean and working right, the waterpump is scouring the layer of rust up you need to dump and refill the rusty water, you do not want pockets of rust inside the engine this can create a hot spot which is not a good thing. So, have patience flush some more water (dont use any more coolant until the rust problem is solved, its wasting money) iTS unlikely a water jacket has cracked, its a lot more likely the head gasket has gone. good luck, if the head gasket is border line you can try bars leak the black goo in a can, old timeer car racers love that stuff, and if the radiator is good, (I know the water pump is, it blasted all that rust loose off the bottom of the water jackets) then it should help its worth a try, makes everything black and oily,in the radiator, but it has a water pump lube which is CRITICAL RIGHT NOW, and it may fix the head gasket issue at least for a while. good luck