I'm not entirely sure, but provided that there is physically a way to remove the stock cooler without damaging the PCB or GPU die itself... I think it would be difficult to deny warranty entirely. I realize that companies will get away with whatever they're allowed to - but I think explaining the
Magnuson–Moss Act in a 'legal' (or legal sounding at least) correspondence to the company would at least change their tune in a
specific situation even if they 'usually' denied similar warranty claims. Of course, there's only an issue if you actually have a reason to file the claim in the first place, and if the cooling is as good or better than the OEM solution - that's even less likely to occur.
If it works for cars, then it certainly works for computers as well. I had a decent amount of experience with this in my 350Z where an oil consumption issue that was clearly a design flaw in the engine as assembled at the factory was repeatedly explained away as being the fault of owners that had put aftermarket turbo and exhaust systems on their cars. Granted, they did manage to force everyone that was getting a replacement longblock to arrive at the dealership with their car returned to stock - prior to the engine swap - but that's certainly expected. Just like in the case with GPUs - I definitely wouldn't expect to get a warranty replacement for a card shipped to them with a waterblock on it... however, if you put the stock cooler back on and shipped it to them - it's against the law for them to say your use of an aftermarket part invalidated the warranty.
