at what temp do you have to worry about scorching the heads? my t-stat went out on me during my drive home tonight. i already have a new 180 to put in with gasket luckily. after reading some threads on here i am worried i may have hurt my heads. i also need good instructions on how to flush the coolant system. this will be my first time ever and i don't want to mess it up. is there anything to put in it while your flushing that will help clean the gunk i can see in my coolant resivoir out? how do i burp the system? i have seen some instructions on here but i'm not sure what the crossover is. thanks in advance for any help i can get.