Nothing was found on the garage floor or driveway.  The previous mechanic didn't find any signs of leaks but antifreeze was being added from time to time.  Hummmmm, where did it go?  We pressure tested the system and it kept leaking down and we didn't find any visible leaks either.  So, that means that the leak is internal and the engine is hemorrhaging.  We know that oil sits on top of coolant (antifreeze), therefore it should be the first thing we see when we loosen the oil pan drain plug.  Sure enough, coolant came first followed by the engine oil (we got it on video to be released to a YouTube channel near you).  Over time antifreeze and oil will combine under the pressure of the oil pump and form a milky substance.  This milky substance (shown in the red circle) collects in the engine like moss or cholesterol and hampers proper lubrication.  Like cholesterol, this sludge can be a silent killer to your engine.  And by the way, this vehicle only has 46,191 miles!  The lesson here is that you should never be loosing any fluid without knowing where.