Submersible water pump water keeps shutting off

Recently setup a water cooled spindle and I have 2 different submersible water pumps. They both will shut off after a few minutes of running. I can pause the carve, shut the spindle down, unplug the water pump and wait a couple minutes before plugging the water pump back in. At this point the pump will start up again but then run only for a few minutes again before the cycle is restarted. One pump is a 3500L/H and the other is 3200L/H. I have tried keeping the return line above the level of the fluid in case it was a back pressure issue but with no change in the situation. The pump is completely and well submerged. They are both 110v pump and the electrical supply to the plug is fine. I am using 2 gallons of distilled water mixed with 1 gallon of 100% antifreeze. The fluid gets slightly warm but no where near being hot.
Has anyone experienced a similar situation?