I ran only 2 fans on my triple rad for a while when one broke and it did OK, I was overclocked and running games too. Of course temps weren't as good but it was OK. Don't try and run them at 4 volts though, even if they do spin they won't move enough air to be worth much. Yate lows at 7V is going to be really quiet so I'd just do that and keep all the fans on.