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.
You do know you have a pressure cap because when the water's under pressure the boiling point can be higher without actually boiling that's how the whole pressure cap thing came into play I do imagine so 3 lb probably won't make a humongous difference in a radiator system in a car or in most cars so 12.7 versus 15 lb and using a test of 25 or 26 lb as you can well see is not going to be really problematic The 12 lb cap is probably giving you ample boiling headroom without any extra pressure The 15 lb will give you some more boiling headroom with 2-point whatever more pounds in the system probably not going to affect very much at all but the boiling protection you get from the other 2 lb I guess to somebody could mean something so the manufacturer I'm sure tries to pick the lowest pressure with the reasonable amount of boiling protection without putting undue pressure on the system causing it to need excessive maintenance and the repair. People used to play with radiator cap pressures all the time and now they don't
I am old school. When I was still active in the trade 15 psi was more or less standard. When I converted 88 kPa to psi I was surprised to see 12.76psi. I agree, not that 2 pounds is going to make a big difference but it just took me off guard. I checked and the 88 kPa was the correct part. Physically the two caps as far as I can tell are interchangeable so it makes me wonder why the two different parts. Manufacturing two physically identical parts with only 2 pounds difference. ????? Then when I looked in the service manual and it said to test the coolant system at 25.6psi, the two pound difference only became more confusing. In the olden days we might put a lower pressure cap on a weak system in hopes of giving the customer a little more time. Just thought I would pass along my findings, not wanting to share my confusion.
I was pretty sure that was the manual you meant, but I was asking what troubleshooting procedure in the manual that particular instruction came from. If they had a procedure for testing the cap, they would probably say to use a pressure near the cap rating. If it was a procedure to test the system for leaks, they might have you connect the pressure tester in place of the cap, and then pump the system to a pressure higher than the cap rating. The latter seems to be where dolj found the instruction came from.
You are right. It says to pressurize the coolant system with (radiator cap tester) to 25.6psi. Strange that it does not mention testing the radiator cap. The manual we are both referring to is Toyota-Prius-XW20-2003-2009-Workshop-Manual. I downloaded it sometime ago and seems to be an exact fit for my 2007.
