Replaced coolant now it is black!?

[Wärmen]

I changed the water pump last weekend and replaced the coolant at the same time. My coolant turned black right after the change. (It was clear before.) I noticed a bit of black sediment in the reserve tank so I´m guessing that the new coolant has dissolved sediment in the engine, but what´s the origin? Head gasket? oil cooler?

Five days later and the temperature is warmer than before and I don't think it is building pressure in the coolant system. No leaks. No smoke from the exhaust. No coolant in the oil. The radiator cap is looking suspect to me for the lack of pressure in the system, but before the pump change I had to loosen the cap so it didn't push out water from the weep hole. It was running cooler then too.

I just looked outside and the coolant is clear again now that it is cooled off.

wut

I am confused


/Wärmen