If it's boiling at a temperature that's too low, then it can only be the result of not enough pressure or improper coolant mix, or a leaking head gasket. You have ruled out the leaking head gasket. You have replaced the coolant. You have tested the system for pressure and found it good. Did you check the new pressure cap to verify that it was holding pressure?
Last edited by dcotter0579; 02-07-2014 at 11:07 AM.