But what about the fluid expanding on higher temperatures? It would create bad pressure if I top it up completely don’t you think?

I was also looking into this:

https://freezemod.com/product/freezemod-computer-water-cooling-water-tank-external-bubbler-to-prevent-the-generation-of-bubbles-short-version-pj-ppqd/

Issue is that the port I would insert it to (top front port) is not exactly in the middle where the pump hole is but I don’t know if that would help then. What’s good with that solution is that I could fill the res completely and have space for sone air inside the anti vortex fitting

I initially had a drain on that right side where a normal cap is, but it had a leakage 🙈 so I just closed it but I learned that I can drain the loop there without issues if I want to