UNUSUAL ANTIFREEZE LEAK

1999 CADILLAC DEVILLE - UNUSUAL ANTIFREEZE LEAK

The car does not overheat. The vehicle leaks antifreeze near the rear of the
engine on the driver's side. A new water pump was installed which the
mechanic thought would solve the problem because a slightly leaking water
pump gasket. The leak does not occur until the vehicle has cooled down
about forty-five to sixty minutes later. I go outside to look under the car and
the leak is there on the cardboard which I replace regularly after driving. The
leak saturates the card and leaks onto the concrete. I normally must put one
to two twelve ounces water bottles of antifreeze back in the antifreeze
reservoir after the leak appears. There are no leaks once I replaced the
antifreeze. The car does not overheat. A pressure test was conducted by the
garage - twice. The mechanics are baffle. The engine temperature normally
gets to about 213 degrees while driving around in the FT. Stewart, Ga area of
90 degrees running errands. There are no leaks when I stop at this store or
that store to make purchases. I have been out as long as an hour at a time
the last three weeks. The car drives beautifully. This car is well maintained.
Can anyone help me or steer me in the right directions? NOTE: How do I
remove antifreeze stains from my driveway?