To use a pressure tester is about the only way to find it. So many times the leak is at the very top of the radiater and slooooow, or at a place where the engine heat evaporates the water before it can be seen dripping.
yeah, What he said, had a POS ranger that did the same thing. small leak at the top of the rad and would evaporate the coolant as it ran down the front of the radiator before it was able to drip... turned the temp gauge into an "add coolant" gauge. :lol: