98 windstar. Cuts out and engine smokes.

Hello all.  My father has a 1998 ford windstar.  He is having a problem with the van shutting off, while driving the engine will quit and smoke(possibly overheating though the temp gauge does not move and the antifreeze is cool to the touch).  The coolant resivoir overflows when stopped after driving(I assume it does it while driving too).  However it does not overflow when idling.  He had me replace the water pump, but it does the same thing, also antifreeze is brown.