Unlikely. Most companies, aside from very specific endeavors, will immediately invalidate any warranty coverage the second you start modifying the card, or whatever kind of hardware it is, in a way that it was not intended to be used. Obviously it goes without saying that in some cases, like where they sell coolers specifically intended for use with certain hardware, that is probably not going to invalidate the warranty if it still has one, but you'd better know exactly what you are about before doing so.
How "old" is this "old GPU" and what do you mean by "turn it into a water block loop? Do you mean, "remove the cooling fans and add a water cooled loop to it"? Is this loop something that was intended for use with this card or are you intending to build some kind of custom loop from scratch?
How "old" is this "old GPU" and what do you mean by "turn it into a water block loop? Do you mean, "remove the cooling fans and add a water cooled loop to it"? Is this loop something that was intended for use with this card or are you intending to build some kind of custom loop from scratch?