The normal operating temperature on most engines is 180 to 200 degrees which generates a pressure of 8-12 pounds. This is true for both carbureted and fuel injected engines. To blow the cap of the radiator the coolant would have to be 270 degrees. Hopefully, the engine would be shut down prior to getting this hot, keeping the coolant inside the radiator. But for added protection, we offer a new 22 lb. radiator pressure cap. This cap works on all of our radiators.