There's probably a difference in the thermostat. The come in different degree ranges as mentioned above. It's stamped on the old and new one. Another possibility is that there's a bubble in the system that was not bled out and this will yield higher temps 8-10 degrees C. To get rid of the bubbles, park the car front up a hill or curb while warm and open the bleeder screws a little. If there are bubbles that come out, you will have fixed the problem.
Steve