Since most of us use these spindles at nowhere near the rated current, just look at the current readout whist it's running to confirm that, you can get away without pumping the coolant for some time. If the body of the spindle is cool, and it's full of water, then it wont be much hotter inside. You should still use the pump in general, but for 'emergency situations' it's fine to run it just not at 100% duty cycle or at a high current.