At used car lot... There was one ( I forget what it was, Pontiac Sunfire maybe ) that dumped a good bit of coolant after a test drive on Saturday. Customer said, "fix that and I'll buy it". So while I was there on Monday they had it running with the hood up and could not find source of the leak. Then the thermostat opened and a stream of water spewed from a crack in the top edge of plastic coolant reservoir. The guy standing at right front fender got a wet shirt. It was one of those newer setups, pressurized reservoir, no cap at radiator.