Keep in mind that when you fill the system and start the engine, its going to circulate, perhaps get water from the heater core, the thermostat will open etc.
I'd flush a few times with regular water like you did just now. Drain from engine and the radiator drain. Fill up, run the engine until...
I wouldn't run the engine while flushing like this @Pr86yota
The garden hose method, do without running the engine. Just open the petcock, engine drain, let it flush.
When draining clean water, then close it all up, fill it up and run so you can flush the heater cores.
I really doubt you messed anything up. Its hard to, when you're only running the engine for minutes at the time.
- I would recommend doing like a garden hose flush since its still so brown.
- Open up the engine block drain all the way, take out the thermostat, let it flush until the water out...
Can you expand on that last sentence?
" However, it looks like it’s still bubbling up almost immediately.. do you think that’s a sign of a head gasket issue or just overheating very quickly. (New water pump has been installed btw) "
So you refilled it with fresh water.
And as soon as you...
Doesn't look bad to me.
It is normal for the coolant to be brown when flushing, especially if you use flush chemicals and if the car has been sitting for a while. I can be brown for like 4 flushes.
I'd flush another time or two with distilled if you can, fill her up with your preferred coolant...