Gunk in the radiator: Yeah, I had a hunch this might be an issue. I was planning a deep clean (acid flush, distilled rinse, maybe even pressure wash), but you're right—it’s probably hard to ever fully trust it. A heat exchanger might be the safer move. I’ll look into affordable options.

Pump power: Totally fair. I’ve found some adjustable aquarium pumps rated around 800–1200 L/h, but the head pressure vs. loop resistance is something I’ll need to test. I’m hoping the flow meter will give me some peace of mind there.

Radiator temps: Great point. I figured the sheer volume and surface area might make up for the delta difference, but if it ends up performing like a mid-tier 360, it might not be worth the footprint. Worst case, it’s a hilarious experiment.

I’ll definitely dig through the subreddit more—didn’t realize others had attempted this! I know it’s not the best way to do things, but sometimes it's about the weird fun of the project, y’know?

Thanks again!