I have not had a problem with overheating on mine yet. They will go up to the right side mark (170*) and then you can see the thermostat open and the temp drop.
I never noticed the difference in size but the 1772 is about 2.25" and the 1572 is about 1.5". I learned something new today.
The 1572.
1572 Radiator.jpg
The 1772.
1772 Radiator.jpg