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Getting Discouraged with my MJ (radiator issues)


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On 2/25/2023 at 1:25 PM, Pete M said:

so what system do I have?  everything is stock 88 but the radiator has a cap.  :dunno:

The Macs Tank uses a standard open system radiator cap.

 

On 2/25/2023 at 3:03 PM, Pete M said:

 

my 16# cap has never popped.  :dunno: 

 

does fluid regularly flow in/out of the cap on that macs tank? 

 

it may be semantics, but I feel like I need to know what makes what before I make suggestions to other owners.  :( 

Yes, it flows in and out of the open system radiator cap. The Macs tank uses the same cap that would be on a later model jeep that has an open system.

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Ok, so this is more of a fluid dynamics issue than anything else.  You are killing radiators because you are over pressuring them,  This is because of the overflow pressure cap being at the expansion tank.  Because of line size and dead-heading the system BECAUSE of the heater cooler lines still running through the Mac tank, the pressure builds in the MAIN cooling circuit (engine, upper/lower hoses and radiator), with no way to relieve quickly. 

 

Put a straw in your mouth, now try to blow out as fast as possible....  take the straw out and do the same.  Which relieves pressure faster?

 

It will be a fully functioning OPEN system if you eliminate those heater core lines and run them directly to the heater core.  An open cooling system is a NON PRESSURIZED system... at least nothing over the pressure rating on the cap on the radiator.  Honestly, you may STILL over-pressure the radiator and force leaks, because the radiator cap is not on the radiator.  

 

OR...  you NEED to put a solid cap on that aluminum expansion tank, and get rid of the overflow bottle entirely.

FYI... There IS NO NEED FOR AN OVERFLOW BOTTLE on a closed cooling system.

 

Its one or the other with the way you have this set up. 

 

You can put an open cooling system radiator into a closed system setup, because the pressure relief is still at the radiator (AKA the main source of antifreeze volume and pressure), not at the expansion tank.  Its not suggested because its overkill to have a expansion tank (with a normal sealed cap like factory) AND an overflow bottle, but I don't see why it wouldn't work. 

 

 

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Pressure works in all directions at the same time. The pressure is going to be pretty consistent through the entire system. Restrictions in the flow may cause slightly elevated pressure in certain spots, but they’re going to be in the hottest parts of the engine, not the radiator where there’s cooling and contraction happening. The pressure in the radiator is never going to be substantially higher than the pressure in the reservoir. 
There are tons of people running a 22psi Volvo cap on the reservoir and they’re not blowing up their radiators. Running an open style cap rated for 16psi has nothing to do with the radiator problems. 

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On 2/27/2023 at 5:00 PM, fiatslug87 said:

I fill them to the top and use the 2.5L overflow tanks.

F4D54865-2323-4A42-942D-E44082392BBF.jpeg

Have been running mine that way for that many years too. So simple. Especially since the 2.5 expansion bottle bolts right in. The mounting holes are already there.

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Sorry, I'm not on here as much as I used to be. I'm the mechanic working on his truck. Both of the welded aluminum rads hes had have leaked from the same area, from the fin solder joints at the top right. I assume this to be a quality control issue with the chinese parts. Beyond that, the Macs tank has been great, and we have this truck running great. Hopefully this newest one from a local supplier will be better, at least it will be easier to work a warranty return, though with new parts, we shouldnt have to worry about that. But we all know how crappy a lot of parts are nowadays, and it doesnt appear to be getting any better. 

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