[4g63tcrazy]

Halon is correct. That front hole is for a coolant line that comes off the waterpipe. The one in the back goes to a port on the thermostat housing. I have always ran coolant through 16g's but on my colt I just ran oil through it since it was a budget project and I couldnt find my old lines. Turbo held up fine, but I would definatly recommend running coolant through it.