[Putershark]

Either impeller or sticking Thermostat. I would first try flushing the engine for 10 min or so by using the flushing port making sure the all the drains are clear and then try again Either way, sounds like some pretty low hours to have such issues unless the engine has been sucking up a lot of sand and junk into the cooling system and if not, then I would think that a defective thermostat would be considered a warranty issue.