coolant boiling/overflowing help.

[talonite]

im hoping someone can figure this out. Everynow and then after driving for a little while i will get home and my coolant will be spurting out of the overflow container and be boiling too. i have replaced both the sensors, water pump is flowing fine(the weep hole looked ok, and i saw it flowing with the cap off) i just replaced the thermostat with a 170degree one and also the radiatior cap, i just put in an aluminum with two slim fans. I cannot figure this out, i thought i had it controlled for a while but then it just came out of nowhere again. I have never had a problem at night my dsmlink has showen the highest i have ran was like 150degrees at night.