pull the thermostat first and replace it. I would do a compression check first BEFORE YOU pull the head, water will come out the tail pipe that is from yout CAT doing it's job. if the head is warped it will have to be resurfaced by a machine shop. I would have all the vavles checked also.when you drained the rad. to replace it was the cooled coolant color ? or oil in it ? not the reserve.

2001 5sp. K&N stock filter 215/70/15
If your check engine light is on at least you know the light still works