Just thought I would pass along a little information that I learned. The radiator cap for a 2007 Prius is 16401-20353 rated at 88kPa or 12.76 psi. This surprised me because I am used to seeing pressures somewhere in the neighborhood of 15psi. Why the lower pressure, I can't say. There are parts outlets that will sell you (this will fit) a cap that is rated at 108kPa or 15.7psi. In fact it is very common on other Toyota engines. Here is the real kicker, this is the instruction detail in the factory service manual. "Using the radiator cap tester, increase the pressure inside the radiator to 177 kPa (1.8kgf/cm2, 25.6 psi)" Make of it what you will.
It says that in the 2006 RM (for one) that is floating around. The purpose of that instruction is to find leaks so the pressure has to be far higher than it would be in normal operation. The testing scenario does not relate to the normal operation.
