my car has been overheating even if i drive for 5 minutes. I checked the cams, and dipstick for white milk shaky fluids hoping its not a blown head gasket. There wasn't any so it seems ok. I try and bleed the cooling system but water wont come out, so I'm guessing the radiator is clogged or the thermostat isn't opening. I took out the radiator and thermostat and find brown gunk in there, and all over the hoses. I'm wondering what is the cause of this and is there any way to fix it?
-Thanks in advance
Thermostat

Where the thermostat sat

Where the 2 Radiator hoses go

Radiator Cap and where it sits
