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plans for open cooling system conversion (I have searched)


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After blowing a tank and heater hose in my 23 year old (original) closed system I am trying to convert over to an open system. I've read extensively both on here and other forums and come up with a game plan, keep in mind I'm trying to do this real inexpensive.

 

1) Pick up a radiator from ebay for ~$60

 

2) Pick up 97+ XJ heater hoses from dealer or local parts supply

 

3) Drop the radiator in, ditch the heater control valve, connect hoses directly to heater core. I just replaced the tstat so that is new.

 

I do not have an electric auxiliary fan so I won't have to worry about wiring that. Now for the recovery bottle...can I convert my old (new) bottle to open style...and if so how do I go about doing it? Where does it connect to the new open cooling system, and with how many lines (1 or 2)?

 

And finally, what fundamental change in the system allows it now to be run in an open fashion? Is it the type of radiator with a filler neck on it? I've searched for this answer and can't really find it unless it's right in front of me...

 

Thanks in advance.

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A lot of MJ/XJer's do this conversion, I've thought about it but my closed system 4.0 89' MJ runs cooler than the three open system 96XJs I've had. Could be that I've got an AX-15 in the MJ and the XJs were all AW4s. For now I'm really happy with the closed system, it is a little tricky to get it completely burped though.

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My suggestion is to get rid of the "old" pressure bottle, install an overflow tank that was designed for the purpose. The old bottle is not vented,which you need to have for this conversion.

The key to the open system is the radiator cap, the spring is designed to keep X psi in the system preventing boil over.

The closed system relies on being (closed) to maintain pressure thus preventing boil over. The pressure bottle on a closed system is designed with some "open" space to allow for expansion as the system gets hot. This system doesn't allow for coolant flow back and forth between the radiator and a vented overflow tank.

 

In other words your nearly there, get the proper bottle. IMHO it's not worth ditching the heater control valve after all this work, just swap to the newer heater control valve (JY is your friend) and you should be good to go.

 

Lastly, the closed system worked for many years. With a good pressure bottle and proper system "burping", I feel that the closed system can be made to perform as designed.

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Dump the closed bottle, rats nest of hoses, & heater control valve and replace with an S-10 overflow bottle. You can modify the closed system bracket to fit the S-10 bottle and it fits great. You also don't need to buy XJ hoses at the dealer. Standard hoses covered with plastic conduit work just fine. I also added an HO thermostat housing so I could use the temp sensor as a bleeder screw.

I did this 6 months ago and it works fine. If you'd like pics let me know.

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Thanks for your replies.

 

1987 Comanche, that would be great if I could see your pics.

 

I was initially of the thought to stick with the closed system because that's the way it was designed, and if burped properly and taken care of worked just as good. That was until my tank burst not once but twice, and a heater hose split open (mind you the hoses are original, and I did burp the system by jacking up the rear and taking out the temp sensor). I figured not only should I replace the original hoses, but the original radiator too...and while I was doing all that, why not convert to an open system that is easier to fix should I be out on the trail or in the middle of nowhere if something goes wrong.

 

So if I understand correctly, the only difference is the radiator cap which makes or breaks a closed / vs open system.

 

And the overflow tank gets fed with a line directly from the radiator?

 

Any special procedure for refilling this system? I assume juts fill it from the radiator cap and don't worry about burping it because it's open.

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Send me a PM with your e-mail address and I'll snap a few pics for you. Maybe you can post them here as well (photobucket isn't playing nice with my computer).

 

 

So if I understand correctly, the only difference is the radiator cap which makes or breaks a closed / vs open system.

 

And the overflow tank gets fed with a line directly from the radiator?

 

Any special procedure for refilling this system? I assume juts fill it from the radiator cap and don't worry about burping it because it's open.

 

To your other questions: Yes the cap and the fact that the overflow tank is vented to the atmosphere. Correct. There shouldn't be any special procedures but I had to pull my HO t-stat housing temp sensor/bleeder screw a few times to get all the air out.

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1) Pick up a radiator from ebay for ~$60

 

That's what I did, just make sure it has the bung for your fan temp sensor on the drivers side. Make sure you buy either a Stant Superstat or OEM TSTAT in 195 degree flavor.

 

 

2) Pick up 97+ XJ heater hoses from dealer or local parts supply

 

I just picked up about 8 feet of some bulk IIRC 5/8" coolant hose for the heater core lines. That'll save ya some money. One of the fittings is slightly larger at the firewall, but a managed to persuade the hose over it. Be careful to not apply and side load to those heater core fittings though as I've heard their somewhat delicate. I had no problems with it.

 

Put a vacuum cap on the valve line and zip tie it to the firewall. Personally, I rather have coolant circulation through the heater core at all times, to help prevent corrosion. My A/C still works and have coolant circulating through the heater core does not affect interior temps even in the Alabama heat down here.

 

For the coolant bottle, I was running a junkyard HO tank, but it did not fit very well into the space, so I found one from a '95 Suzuki Sidekick that fits nice and works well.

 

I'll post some pics of my setup in a bit.

 

Enjoy your new simplified cooling setup, FWIW my temps never get to the halfway mark on the gauge anymore.

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Comanche09,

 

That looks great, exactly what I want to do by simplifying it and by simplifying it make it more reliable with less parts / opportunities to fail. Thanks for the pics...only thing is I don't have an electric fan so I won't need that port on the radiator to plug it in, and if in the future I want to add one I can either put it in wired to a switch or put the sensor in a HO Tstat housing which should be an easy switch.

 

With the recovery bottle, does the line run from the radiator to it, or is there some place else in the system it plugs in to?

 

Thanks everyone for your help I can't wait to get this done and get her on the road again.

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I've found that an early-ish tracker/samurai overflow bottle works pretty well if you don't mind some really simple fab work. About 6-8" of flat stock, some tapping, and it attaches to the bracket for the charcoal canister and is a pretty good spot to still let you get to anything you need to.

 

Not the best pic for showing this, but...

LQ_DSCF2413.JPG

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Comanche09,

 

That looks great, exactly what I want to do by simplifying it and by simplifying it make it more reliable with less parts / opportunities to fail. Thanks for the pics...only thing is I don't have an electric fan so I won't need that port on the radiator to plug it in, and if in the future I want to add one I can either put it in wired to a switch or put the sensor in a HO Tstat housing which should be an easy switch.

 

With the recovery bottle, does the line run from the radiator to it, or is there some place else in the system it plugs in to?

 

Thanks everyone for your help I can't wait to get this done and get her on the road again.

 

Thanks :cheers: Yes you need just one line running from the radiator cap neck nipple to the coolant overflow bottle. Get at least six feet. And yes, it cuts down failure points significanty and bumps up piece up mind big time. :thumbsup:

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Well everything is in and she runs good. I don't have a temp gauge but so far so good, no temp light coming on.

 

Thanks guys for all the help.

 

As a post script I might pickup a heater control valve the next time I'm at a junkyard. I'm not sure if it was my imagination but the cab was unusually warm...figure can't go wrong for a few bucks next time I'm there, worth a shot.

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