Knock sensor?

I would open the TSTAT housing and pour water in and let it flow from the knock sensor hole.. Just let it keep flowing out. Then I would fill the car with pure water and let it run for a bit once everything is done and back together.. Drain it out. If it is clean fill with coolant and call good. If it is still dirty, repeat.

Alrightyy

The build up is totally normal. I often have to poke through it when pulling a sensor. And yes.. that is about the lowest point in the block.

Alright. Freaked me out. Like literally made my heart skip about 15 beats o.O

Yeah, it took probably another 2 ish gallons to fill back up