DECLARE

l_sql VARCHAR2(32767);

BEGIN

l_sql := rpad('X', 4001, 'X');

FOR rec IN (SELECT l_sql FROM dual)
  LOOP
    NULL;
  END LOOP;
END;

SQL> DECLARE
  2
  3  l_sql VARCHAR2(32767);
  4
  5  BEGIN
  6
  7  l_sql := rpad('X', 4001, 'X');
  8
  9  FOR rec IN (SELECT l_sql FROM dual)
 10    LOOP
 11      NULL;
 12    END LOOP;
 13  END;
 14  /
DECLARE
*
ERROR at line 1:
ORA-01460: unimplemented or unreasonable conversion requested
ORA-06512: at line 9

SQL> 3
  3* l_sql VARCHAR2(32767);
SQL> c:VARCHAR2(32767):clob
  3* l_sql clob;
SQL> l
  1  DECLARE
  2
  3  l_sql clob;
  4
  5  BEGIN
  6
  7  l_sql := rpad('X', 4001, 'X');
  8
  9  FOR rec IN (SELECT l_sql FROM dual)
 10    LOOP
 11      NULL;
 12    END LOOP;
 13* END;
SQL> /

PL/SQL procedure successfully completed.