introducing new dog

Question
We have a 1 yr old German Shepherd, and we wanted to get another
shepherd.  We found a 3.5 yr old male GSD who seemed to get along great
with our female. There is no aggresion at all, however, they won't stop
playing.  They absolutely will not calm down until they collapse.  They take
turns chasing each other (lots of play posturing).  There is no food aggression
at all - they even take turns eating from each other's bowls.  If I separate
them, they both begin whining (even though ours has been crate trained).  
They seem to be crazy about each other, but they are driving us crazy.  It
does not matter how much I exercise them, they continue playing until they
crash, and then they get up and do it again.  I have introduced lots of dogs
during my life, and I have not seen the continued hyper-activity that these
guys possess.  Separately, they are both calm and well-behaved.  We have
adopeted him on a trial basis, but I am feeling very overwhelmed after 3 days.  
Thanks for any advice.


Answer
I am a little surprised that he plays like that at hs age.  I guess the males aren't as quick to lose interest in playing as the females.  I don't see a problem.  We frequently accept guests, and that is the way it usually.  they will carry on until they collapse.  We have even had one of our lower windows broken a couple of times.