2013 CT200H, Coolant service, not much draining, no heat

What's up guys, so I'm new to this stuff like a lot of us dipping our feet into "cheap" hybrid tech as we begin to see quality cars pop up for not much money.

I bought a 2013 CT200H, 115k, PO seems to have been good with oil changes and has definitely changed the inverter coolant, but the ICE coolant is gross. I don't THINK it's a blown head gasket, but I did buy the car right because the heat is barely hot (fluctuates to cold) on the driver side and cold on the passenger side. My first thought was clogged heater core so today I bought some flush and SLLC and proceeded to drain what I perceived to be the original coolant. The other thing is maybe air bubbles, but I've not really seen a reliable method for burping these systems like you could with Gen 2.

I got maybe a half gallon out of the system with the drain valve behind the radiator which is significantly less than what I was expecting. I went ahead and put the flush with water in place of what I was able to drain.

The car doesn't overheat at all. On some very steep (Smoky Mountain) roads, at full throttle, uphill for 30 seconds to a minute or more at a time in Sport mode, I saw temps no higher than about 213 via my scan tool. At idle car stays solid at 190ish. This was with the flush/distilled water combo, so temps will likely be lowered with proper coolant in place.

I'm getting ready to drain the flush and refill the coolant, but after that I really have no idea where to go. Seems like I've read hours on here about all the various symptoms and resolutions but I've not seen this issue of the coolant not draining?

Can anybody shed some light on what I might be doing wrong? Really not looking forward to a dealer visit when I've historically done all my own maintenance.

 

Something I just noticed as I continue to wash away the flush is white chalky stuff in the drained distilled water, but I guess this is likely leftover nitrates, at least from what I've read, so maybe no need for alarm there...

Also mods, maybe I posted this in the wrong forum and it needs to be in the troubleshooting section. If so, my bad and thanks for moving.

 

Thanks for the tips on testing the bits, I will check all this out with my fingers crossed. I really thought 115000 was too early for a head gasket failure. Even if that's what it is, I guess I still got a decent deal, just not as much of one as I thought!

Thank you again.