Correct PSI to test cooling system and how to bleed air?

[mcne2026]

I have an overheating issue. The radiator cap failed a pressure test, it will not hold at just below 15PSI. I want to pressure test the cooling system as well, to look for any leaks. What is the correct PSI to test the cooling system? I will also be replacing the thermostat and flushing the cooling system with Thoush.

How do I bleed air from the system after I refill it, when I am done with the project? I could not find a bleed valve in the service manual.

Thanks.

 

[Jake0147]

I usually add twenty five percent or so, but it's better to get the needle to an exact spot on the gauge than to get an exact pressure to test at. (The water pump makes enough pressure in the engine anyhow, that you wouldn't want to apply that much to the radiator, so you aren't shooting for a "max" to check for blowouts, you are checking for existing leaks). So eighteen or twenty pounds would be perfect for a 15 pound cap.
If you're using a tester that doesn't get used daily, or at least frequently, and it doesn't hold pressure right but you don't see a leak right away... Don't forget to check the tester, sometimes the diaphragms dry up a little, they don't make a lot of noise and are easy to overlook.
Go ahead... Ask me how I wasted an hour this morning and why that tidbit is on the top of my mind today...

 

[mcne2026]

I think 18 to 20 is way to high. If the radiator cap pops at 15, then the correct pressure for the test would be below that. I am looking for leaks, but I am also looking to see if it holds pressure. I am also going to test to see if it builds pressure, IE headgasket issue.

So, anyone know what the manual says to use? I can not find it in the TM.

Also, still looking for the bleeder valve. Thanks.

Anyone have TM 750-254 they could email me? robert@mycoolcabin.com

 

[Jake0147]

...If the radiator cap pops at 15, then the correct pressure for the test would be below that...

If you look at several brands of proper radiator tester, you'll find many have color coded "charts" on the gauge. Depending on the brand, you'll find anywhere from one to two pounds over the cap, all the way to 40 percent over the cap. This is why I say that an accurate starting mark is the biggest key, you'll need to walk away for quite some time to do a conclusive check.

Remember, the cap is not a "safety valve" or "blowoff valve" like you'd have in a water heater, it operates (vents) every time you drive, and off and on the whole time that you drive as a part of normal operation. It is a two way valve that actually sets and actively regulates the operating pressure under which the system operates.

But as I said, you are checking for existing leaks, not the possibility of new ones. If you're more comfortable at the cap pressure, then go with the cap pressure. I can't see any reason at all to go with less, as the system does not operate at any less, and the section between the water pump outlet and the engine side of the thermostat, that will most definitely see pressures that you don't want to test the radiator at.

 

[cranetruck]

This may be enlightening:
Steel Soldiers :: Military Vehicles Supersite