I had the same idea a couple months ago!! Didnt manage to make a prototype or a coherent model but looked if this can be feasible and how it would perform.
First, a guy at the evga forums managed to make a "waterblock-first-air-cooler later" that ends up looking like if an ekwb block and a dinatron server cpu cooler had a child and he ended up with usable temps running only with air.
Other thing to consider is that unless the heatsink is super efficient it wont help temps while using a custom loop (neither the custom cooler or that chinese cooler that Gamers Nexus tested benefited from running fans at the heatsink once on water)
But im loving the idea that an sff case can be modified to use a external rad without the need to have it pluged in all the time. So im hoping to see some prototypes from you (plz if you do, i want one
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