I'm sure that Kitwn is right in saying that you could get much more coolant flow with bigger tubes, but in my own case (usual 2.2KW motor) I use a small pump designed for a caravan water supply, fed from a 5L bucket under the bench I have a switch that allows me to feed the pump from its design 12V, but almost always (except when filling) run it on 5V. Slow flow but the motor case temp never gets more than a few degrees above ambient. OK, I probably don't drive my machine that hard - I'm generally cutting things where other constraints rather than spindle power apply - but you might not need very sophisticated coolant setup. I've been running that spindle setup for a few years now, including runs of hours rather than minutes. As always, though, what you are going to do with the machine might change this.Most people use these big spindle motors because of the ER20 collet size rather than needing that much power.