Performed a coolant flush when changing the OFHG. Glad I did, as the coolant didn't look like it was in the best shape.
Rad Plug
Drained just shy of 5L from the Rad
Removed the thermostat pipe to get the rest out of the block. The pipe is on there pretty tight, and it feels like you're just about to break the plastic connector when the O-Ring finally lets go.
Same pipe shown from both the top and the bottom
Drained another ~750mL from the block, for ~5.5L total.
Ended up putting about 7L back in. No CEL, but it was obviously low on coolant before.