I ran our  JD vac planter for the first time this year with my 3545 MF tractor.   Used to pull it with the  4450,  and  even the 4430 in the early years of the planters' life.  Worked fine with the  open center.

Both JD's are closed center,   but my MF is  open.    Oil temp is going to be higher with the open center. It's just a  fact of physics.    It's going be important to  make sure to route the discharge  the return flow directly to sump.  If you just  hook the discharge back to the service valve outlet,   some of this extremely hot oil is going to  be recycled back into the charge circuit.  A fairly large portion is routed  directly back to the  intake side of the  Hyd pump,  without the benefit of cooling in the sump.   Dumping 100% of return  to sump  at least  ensures  some cooling before  starting over again.

a  open center  in neutral makes very little pressure in the  circuit.  Very little heat, very little drag. 

  When you  pull the lever, ALL the oil in the circuit is  forced  down the work path,  and if  the work  is less than  what is being supplied,  then the relief valve  dumps the excess  back to  sump.   Oil flowing over  either   the work, or  the relief is going to  make pressure (system rating)  and  this is where the heat comes from.    Neat thing about  the closed center, is  that they only supply  the exact amount of  volume as  what the work requires.  No gobs of  excess flowing over a  relief valve making  even  more heat! 

Even  on our  4430,  we  were told to dump the return directly to sump.   My   8 row planter uses a tiny orbit motor, and the 4430  was able to keep up.  Apparently,  by the time the 50 series  came about,  it's ok to just use the service coupler for  return.  It had higher capacity pump.   

Closed center also relies on  a certain amount of  return to  supply the intake side of the pump.

Ever notice  when you lift a  single action cylinder  dump wagon,   how an  early JD  will chatter  after lifting  about  halfway up?    It needs  time  to recharge its  internal  reservoir..  and  can  continue  after waiting  just a couple seconds.   It's  'starved'  because a  single  action  cylinder doesn't send  return back to the intake side of the pump.