Radiator Pressure?

I finally pulled the plug a couple months ago and upgraded to a Cold Case radiator and went from a closed loop to open loop. I also got a high flow water pump and a triple e-fan setup on a smart switch and cabin mounted monitoring and control (this would be NickInTime's Trinity Fan Controller). When the radiator is full, I never, ever see overheating. However, I have leaks and this is where my question is.

I performed a full flush, but it took 3 months for the obvious leak to develope: freeze plug. Well before this, after 1 month, the radiator had some mystery leaks. It would leak and then not leak. The drivers side radiator hose would sometimes leak from the engine side fitting. It's been tightened and loosened trying to find a spot where it wasn't too tight but tight enough, and can't find it.

Observations: radiator cap has never released built up pressure. I am positive I don't have the overflow tank hooked up, but it's atmosphere pressure, it's not stopping the radiator from venting. The lower radiator hose and upper radiator hose build up a ton of pressure, I don't have a gauge to say how much, but a 15 minute ride gets both hoses very hard. They are flexible when cool.

Is it possible that the radiator cap from Cold Case is functioning incorrectly or malfunctioning? Shouldn't the cap release pressure? Could this be causing at least some of my issues and also creating new ones (such as the freeze plugs)?

Thanks everyone, I will post pictures and get advice for the overflow bottle later

Corrosion and failure of the freeze plugs is not unusual.

Have you replaced the radiator cap to confirm it is not faulty or the incorrect pressure rating ?

That's what I figured for the freeze plugs, especially since I did a chemical flush of the water jacket before installing water pump, new thermostat, and new radiator. Failures at the freeze plugs was expected. I haven't yet got a new radiator cap, what temp release should I be getting?

Pressure release, or temperature release

16lbs is the stock specification.

Thanks! I haven't been able to upload pics here yet, but I have pictures posted on Cherokee forums, same title as here

Just thought I'd offer a few pressure measurements for background. My 96 XJ has no radiator/cooling system leaks, but I had repeated radiator cap (Crown) leaks. I installed a mechanical pressure gauge tapped into the upper radiator hose. Running a Stant 16 psi cap, the system routinely runs up to 18 psi with cooling system temperature indicating 208 to 217 F. Under those conditions, depending on load, AC, rpm, etc, the pressure oscillates from 7 to 18 psi and has a general of more/less average pressure of 12 psi. Over night as the system cools the pressure drops to negative 3-4 psi before releasing the vent and drawing liquid from the reservoir back into the radiator. In the morning, the indicated pressure is always at 0 psi. I tried unsuccessfully for weeks to get one of the radiator cap manufacturers to tell me the specs on when the vent valve on the cap would release, so I measured it. That corresponds to a vacuum of 5 to 8 inches of mercury.

The relief pressure and suction vacuum level vary with MY. The specification for my 2000 16 psi and 0 psi. The suction valve hangs loose on radiator caps with this specification. The other common specification for the XJ is 13 psi. The suction valve on these are spring-loaded and require some vacuum in the radiator to open. Both fit.

My XJ had a 13 psi cap when I bought it. Drove it like that for a year and then switched to the 16 psi cap. The only difference which was unexpected was that the coolant temp varied slightly more with the 16 psi cap. It wouldn't be noticeable if watching the temp gauge, but on my OBD-II logger, the coolant temp would drive above and below the set point by another tick. Switching back to the 13 psi cap made temperatures more stable again.

@xSirCyberx, it shouldn't be too hard to find a radiator leak, especially since you have an efan setup that should some off pretty easily. If it really is leaking, you should get an exchange. I'm sure Cold Case will warranty it.

My aftermarket radiator came with a ridiculously high cap, like 21 psi. With my poor condition junkyard engine and the limited availability of rhd heater cores I didn't even want to risk stock pressure. I run a 6 psi cap and have never had a problem, the water overflows to the surge tank and sucks back in as necessary. No overheating, although higher pressure is supposed to help prevent boil over it has never been an issue, even 100+ heat, stop and go mail delivery.

FrankGRUN said:

Just thought I'd offer a few pressure measurements for background. My 96 XJ has no radiator/cooling system leaks, but I had repeated radiator cap (Crown) leaks. I installed a mechanical pressure gauge tapped into the upper radiator hose. Running a Stant 16 psi cap, the system routinely runs up to 18 psi with cooling system temperature indicating 208 to 217 F. Under those conditions, depending on load, AC, rpm, etc, the pressure oscillates from 7 to 18 psi and has a general of more/less average pressure of 12 psi. Over night as the system cools the pressure drops to negative 3-4 psi before releasing the vent and drawing liquid from the reservoir back into the radiator. In the morning, the indicated pressure is always at 0 psi. I tried unsuccessfully for weeks to get one of the radiator cap manufacturers to tell me the specs on when the vent valve on the cap would release, so I measured it. That corresponds to a vacuum of 5 to 8 inches of mercury.

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Is your16 psi cap vented or non-vented? The vented caps usually have a "V" in the designation stamped on the cap. Or you can look at the suction valve. If it flops loosely, its vented. Or if you know the part number of the Stant cap, that will tell too.