My car is leaking coolant onto the garage floor under the radiator, but my mechanic couldn't find the leak even with a pressure test. He said it held pressure for 20 minutes. So he replaced the radiator cap in case that was the problem. But it's still leaking coolant. What's the next step?
Have you checked the hoses? I had an issue like this years ago with a tiny (and I mean tiny) hole in a pipe close to a clamp which when the engine was running and hot the amount coming out would just evaporate, as it cooled though then it would form a puddle.
So, how much do you find under the car - a spoonful, a cupful or a gallon?