parallel processing - C++ openmp much slower than serial implementation

I assume that you are concerned with the time taken by the entire code inside the while loop, not just by the time taken by the loop beginning for(int i = 1; i < MAX-1; i++).

This operation

if(iterationCounter != 0)
{
    memcpy(oldTemperature, newTemperature, sizeof(oldTemperature));

}

is unnecessary and, for large arrays, may be enough to kill performance. Instead of maintaining 2 arrays, old and new, maintain one 3D array with two planes. Create two integer variables, let's call them old and new, and set them to 0 and 1 initially. Replace

newTemperature[i][j] = ((oldTemperature[i-1][j] +  oldTemperature[i+1][j] + oldTemperature[i][j-1] + oldTemperature[i][j+1]) / 4);

by

temperature[new][i][j] = 
  (temperature[old][i-1][j] +
   temperature[old][i+1][j] +
   temperature[old][i][j-1] +
   temperature[old][i][j+1])/4;

and, at the end of the update swap the values of old and new so that the updates go the other way round. I'll leave it to you to determine whether old/new should be the first index into your array or the last. This approach eliminates the need to move (large amounts of) data around in memory.

Another possible cause of serious slowdown, or failure to accelerate, is covered in this SO question and answer. Whenever I see arrays with sizes of 2^n I suspect cache issues.