Hi - your temperature limit is basically the boiling point of your system, you gave a lot of info on your car in your first post, but didn't indicate the pressure cap that you are running.
At standard pressure (1atm) water boils at 100c (212) i.e. without a cap - change that to a 50/50 mix of water and ethylene glycol
antifreeze in the cooling system will boil at 225°. Pressurizing the system with a spring-loaded cap raises the boiling temperature of the mix about 3° for every 1 psi of pressure. With a 15 psi cap, the boiling temperature will be up around 265° F