Okay, I was hoping that I would never have the opportunity stump you guys because that meant I and my mechanic were stumped and I probably have been separated from a lot of money. I have a 2005 jeep grand cherokee 3.7L. Thought I had a radiator leak, and subsequently replaced the radiator. Drove the car a bit and then noticed after a couple of days a large puddle of coolant under the car. Seemed it was coming from radiator hose and thermostat. Pressure tested but did not seem to show leak. Had pressure. Replaced hose and thermostat. Two days later another puddle. Seems to only happen after 2-3 hours of driving, and only after the car has sat for a couple of hours or so. Does not leak otherwise or show leak with pressure test. Seems like the water pump given where puddle is, but the pressure tests does not show a leak there.
Don’t forget to look at your A.C. drain. If you still can’t find it, for about 5 bucks you can get flouresant dye. Clean engine, put the dye in coolant. Do pressure test. Look for leaks with a blacklight. If you don’t see it drive it for a day or two. When you find a puddle trace it with your black light.
I’d guess it is the water pump itself leaking. Pressure tests OK, but still leaks. Water pump.