What is a snow golem's range?

I want to incorporate snow golems into my mob grinders. How close does a hostile mob need to be in order for a snow golem to begin throwing snowballs?

I tested this by making a hall in creative mode and blocking a zombie in a small chamber on one end and letting a snow golem go on the other. He ran forward until he was 10 blocks away and started pelting the zombie with snowballs until I quit the game.

For those that aren't clear, here's how I counted:

[G][-][-][-][-][-][-][-][-][-][Z]
[0][1][2][3][4][5][6][7][8][9][10]

Their sight seems to be 16, the same as most mobs. I made one 18 blocks away, and he couldn't see the zombie from there.