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So, I’ve decided to finally tackle my coolant system because after 3 plastic bottles breaking, I’ve had enough. I bought an aluminum tank to replace the plastic one and it uses a radiator cap. What I want to know is, what is the pressure rating for the closed cooling system?

 

P.S - I won’t switch to open cooling until I get a new radiator at the very least

 

 

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Once you install the aluminum tank with radiator cap you WILL have an open system.  An expansion tank for a 2.5 engine works very well. It bolts right in. The holes for the screws are already there. It mounts on the drivers side towards the front of the engine bay. You will have to relocate a few things. Then just run a hose from the expansion tank to the fitting below the radiator cap. Fill the aluminum tank to the top and keep an eye on the level in the expansion tank. It has markings for cold and hot levels.

 

I believe the OEM cap for a 4.0 is 13 psi.

 

Hope this helps.

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Once you install the aluminum tank with radiator cap you WILL have an open system.  An expansion tank for a 2.5 engine works very well. It bolts right in. The holes for the screws are already there. It mounts on the drivers side towards the front of the engine bay. You will have to relocate a few things. Then just run a hose from the expansion tank to the fitting below the radiator cap. Fill the aluminum tank to the top and keep an eye on the level in the expansion tank. It has markings for cold and hot levels.
 
I believe the OEM cap for a 4.0 is 13 psi.
 
Hope this helps.

Wouldn’t the tank be pressurized still? I thought that an open system would have an expansion tank that is not pressurized. Or could I plug off that valve under the cap?


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for what it's worth, I have a closed system but with a modern radiator (with cap) and the cap is rated 16lbs and has never popped. 

Thank you Pete! I’ll look into getting one. This little tank is some universal eBay one that I’ll have to fix up to make it work.


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1 hour ago, Dammerung said:


Wouldn’t the tank be pressurized still? I thought that an open system would have an expansion tank that is not pressurized. Or could I plug off that valve under the cap?


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I assumed you had a Macs tank. If you filled the tank half way I guess it might work, maybe someone has tried it. You don't want to plug that fitting, that's where the pressure will escape.

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On 1/13/2021 at 3:47 PM, Dammerung said:


Wouldn’t the tank be pressurized still? I thought that an open system would have an expansion tank that is not pressurized. Or could I plug off that valve under the cap?


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What tank did you get? The one I used takes a radiator cap (I used a 13-pound), and it also has a barb fitting for a tube that goes to an overflow (expansion) catch bottle. This makes it functionally an open system rather than closed. Mine's a Moroso, but the Mac's tank specifically for the XJ and MJ didn't exist when I did mine.

 

Here's the link to the Mac's tank: https://macsradiatorshop.com/product/macs-1987-1990-jeep-cherokee-aluminum-coolant-tank/

 

See the smaller fitting that's ON the filler neck? A radiator with a filler neck has the same thing. That's for the hose to the overflow catch tank.

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What tank did you get? The one I used takes a radiator cap (I used a 13-pound), and it also has a barb fitting for a tube that goes to an overflow (expansion) catch bottle. This makes it functionally an open system rather than closed. Mine's a Moroso, but the Mac's tank specifically for the XJ and MJ didn't exist when I did mine.
 
Here's the link to the Mac's tank: https://macsradiatorshop.com/product/macs-1987-1990-jeep-cherokee-aluminum-coolant-tank/
 
See the smaller fitting that's ON the filler neck? A radiator with a filler neck has the same thing. That's for the hose to the overflow catch tank.

https://www.ebay.com/itm/153133492767

That’s the tank I bought. I think I’ve worked it out now.


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On 1/14/2021 at 5:18 PM, velco said:

Or you can plug the overflow and keep running a closed system.  I am using a 16-lb cap.

IMG_4070.JPG

I love this. I have a few renix radiators in great shape. I'd love to this on an ho just to toy with guys who complain about the closed setup.

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Nice job.

 

You really NEED to either install a catch bottle or cap the fitting on the filler neck. If you don't do one or the other, you're going to be spitting hot coolant onto your starter solenoid.

 

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Nice job.
 
You really NEED to either install a catch bottle or cap the fitting on the filler neck. If you don't do one or the other, you're going to be spitting hot coolant onto your starter solenoid.
 

Yeah that’s next on the list. I didn’t have any of those caps but I’m planning on going to an autoparts store to get them.

Edit: just got a 5/16 vacuum cap and put a fuel line hose clamp on it


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On 1/18/2021 at 8:10 PM, Dammerung said:


Yeah that’s next on the list. I didn’t have any of those caps but I’m planning on going to an autoparts store to get them.

Edit: just got a 5/16 vacuum cap and put a fuel line hose clamp on it


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Okay, by going that route, you have kept it a closed system. That means you should only fill that new tank halfway -- you have to leave air space for the coolant to expand when it gets hot. If you were to install a catch bottle, you would be converting to an open system and you could fill the new tank right to the top.

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