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Just recently temp gauge has been slowly creeping past 210 and ends up in the 240 range. At first I thought maybe bad temp sensor because I'd raise the hood and the engine bay was not putting off a ton of heat and there was no hissing or noise from near boil over. Drove it on an extended trip yesterday evening and although it never went in to the red it was just above it and when I got to my destination I raised the hood and the heater valve was spitting a little. Anyhoo, I've also noticed the last few times I raised the hood that the overflow tank level had not budged...........bad tstat?

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24 minutes ago, HOrnbrod said:

How old is your radiator?

I'm only the second owner but if I had to guess it's original and just turned 220k yesterday, so I'm realizing it could very well be the rad is finally shot. I've only put 10k on it in the 10yrs I've owned it and it was parked for a few years until last fall. It was the original owner's DD and overall it seemed like it was well taken care of when I bought it. I've never done a flush on it so I plan on doing that, and since a new tstat is inexpensive I plan on replacing it with a OE unit as you suggest or a Motorad fail-safe unit. It will be my 16yr old son's DD soon when I get this and a few other things fixed. 

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9 minutes ago, WahooSteeler said:

I'm only the second owner but if I had to guess it's original and just turned 220k yesterday, so I'm realizing it could very well be the rad is finally shot. I've only put 10k on it in the 10yrs I've owned it and it was parked for a few years until last fall. It was the original owner's DD and overall it seemed like it was well taken care of when I bought it. I've never done a flush on it so I plan on doing that, and since a new tstat is inexpensive I plan on replacing it with a OE unit as you suggest or a Motorad fail-safe unit. It will be my 16yr old son's DD soon when I get this and a few other things fixed. 

 

The radiator should be replaced or at minimum professionally rodded out by a good shop and flow tested. The passageways are probably clogged nearly shut as old as it is, especially as it's been parked and not running for all those years.

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10 minutes ago, HOrnbrod said:

 

The radiator should be replaced or at minimum professionally rodded out by a good shop and flow tested. The passageways are probably clogged nearly shut as old as it is, especially as it's been parked and not running for all those years.

I've seen lots of debate on replacement units and/or going to an open system. I'm generally of the opinion to spend a little more to get quality and do it right. 

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18 minutes ago, WahooSteeler said:

Gonna change out the tstat just to see what happens. Question.......going to use a Fel-pro paper gasket, do you guys recommend RTV with that?

I always use a thin layer of RTV on each side of the gasket.  I've been told that the blue RTV is best for contact with water, but not sure if there's any truth to that.  Never had issues other than when I use too much of it and make a mess and cause the gasket to move around when tightening the bolts, etc...  I seem to remember that at least one of the bolt holes tapped in the head for the thermostat housing is not a blind hole (so threaded all the way through into the head water jacket) so I would also recommend using a copper washer (like for a brakeline banjo bolt) on that bolt or use a thread sealer on the bolt threads - like permatex high temp thread sealant:

https://www.permatex.com/products/thread-compounds/thread-sealants/permatex-high-temperature-thread-sealant/

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40 minutes ago, omega_rugal said:

try another sensor before you start taking the engine apart...a hot engine is easily recognizable because it`s... i don`t know... HOT?

 

 

the valve was leaking coolant?

Yes, and just confirmed that again this evening. Put in a new tstat with "jiggle valve" and got it up to temp. Took a solid 15mins before temp got to 230ish, overflow bottle never budged, upper radiator hose cold to the touch. Shut it down and while looking around saw steady dripping at heater valve.  

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There could be multiple reasons. First pull water pump and check that its proper rotation. Next wgile its out pull t stat housing and tstat. Confirm t stat is operating properly by checking it in a pot of boiling water. I will not spend a penny on the duracrap azline again after being frustrated to the extreme of going through the complete closed system style 3 times to find that 3 for 3 tstats either didnt open or stuck at a point. I now check them new every time before installing no matter the brand. Next clean away old gasket and any oil with non chlorinated brake fluid. I always then wet sand a heavy quick grit then a long wet sand with a fine to remove all rust.  Next take a garden hose to the head with a spray nozel and flush that block. Its great if you can unlock your block drain plug but if not no worries just let it pour out the pump hole. Next take air compressor and blow it out best you can at head. Again the water will come out at pump hole if block plug is still in. You are just trying to get water out of way for the gasket to dry clean and remove any rust from the sanding or old gasket or any sediment. I will put a jack under rear diff to raise it to allow more water out of pump hole if the drain plug was too much a pita. Then I jack front up from pumpkin so any remaining water goes to back allowing for a quick dry seal. Yes I'm anal however after owning a dozen renix xjs and mjs with closed cooling systems over the years I have learned that every single time I followed these steps and properly purged the sytem I never had a single issue with cooling again unless something damaged the system allowing air into the line. If its not air tight with air out it will fail period. Even with all brand new components hoses tanks cap and all. You will b buying half of those new parts again. Trust me I have been there it took me 3 times my first time when I first learned to turn a wrench. I like to use black permatex instant gasket. It will set good on hot day. I however will always give it a full 24 hours on any closed system because of the extent of work involved to redo it on a closed system. Now that your surfaces are clean and dry start at pump and work up. I like to put the water tube on the pump first before install so no unnecessary force is put on the gasket. Then water pump. Next I put a couple of dabs of rtv on tstat to hold in place to make the housing install easier. Keep in mind u can use paper gaskets or none at all. The thing to remember that too much rtv is worse than not enough. Not enough you know it leaks or soon will and same problems start. Too much and it stays blobbed hindering flow or worse yet breaks off eventually and clogs. I take a knife blade and spread it an 1/8" evenly to housing lay paper gasket and then do the same again to it. Before doing this though I properly trimmed and made any and all changes to the paper gaskets ahead of time making sure they were not oversized hindering flow which 99% of the time they are. Again take a fresh utility blade trim them first and can even hit them with a fine 2000 grit paper where you trimmed smoothing any rough edges. You can laugh at how anal I am but when I buy a jeep I now toss belt pump tstat housing and pump and radiator. I start over after flushing and am done for however long I own it or wheel it. Follow manufacturers instructions on tighting. Its usually finger tight alternating bolts for the first 1 to 5 min. This varies drastically on temp and humidity especially on instant gasket. The colder the longer it takes. Its easy to go to fast on a cold day. After you done the gaskets and has sat for 24 hrs to fully cure again anal I know connect your upper rad hose to rad but leave it routed but disconnected at tstat. Make sure your lower is completely connected. Take a funnel and fill a t tstat housing b patient repeat until you get as much as possible and then do the same with upper radiator hose. Again jacking the front end up helps drastically now allowing more air to come to tstat housing head area. No matter what there will be air trapped. I like to use the newer tstat design on the renixs thats tapped for the sensor for newer hos. This allows you to remove the plug and put a bolt in for easy air purging or burping the system at any time weather to flush it or repairs. Next open your heater controls up in cab. Now take your heater hose from inlet tube end and max it out with a funel and coolant. Note all this is futile if your heater control valve is bad or heater core. Check to make sure as your topping off this hose bfore hand that vacuum is being applied to the valve to open it up allowing coolant to enter core. Now make connections. Many here may disagree here now with what I do. I have a small hill in my front yard. At this point I would start the truck and point it Nose down on the hill quickly shut it off you should not stress the sytem by running long or at high idol until its purged of air. The air will cause quick boilover and damage new components even the motor if left neglected for a long period like this. It creates a hydo lock to the coolant flow meaning none flowing but pump turns pumping, then it pressurizes. The first thing damaged is your tank cap and maybe tank which should b replaced too. Then it steams over pouring all coolant out replacing it with air being sucked into the system. So now back to nose down. I chock tires and pop hood. There is a temp sensor on the back right next to vavle cover. It has 1 wire with a 90° elbow. Pull off connection carefully since most likely its old and brittle. I think its a 13 or 14 mm. Use a deep well 1/4" drive with extension and pull it now. Clean threads and make sure you have good access to this spot now and can pull the sensor quick and install quick. Practice once it doesn't hurt. When your comfortable take sensor safe rtv reapply to the senser after you cleaned it and install and reconnect the wire. Now get on some heavy mill latex gloves and safety goggles find a a helper its easier. Someone will start the truck the other have wrench near sensor and ready to pull its connection. Usually in a minute or 2 the guage will start to climb. Its hydolocking and overheating which is fine. It needs to get above your tstat temp to open up the tstat for it to start flowing. 185 to 195 is best tstat temp to buy in that range by the way. I have best performance with 195 and they stay constant at a 210 to 212 range on a hot summer day. Now its warmed up to 210 remember water boiles right there shut truck off and work fast pull wire connection and loosen temp sensor. Just bfore its completly loose stop. Take off socket off wratchet. Take a rag and slowly turn the rest of the way with the rag over the socket. You will initiallt feel the suction. The suction is good for the fact you know the system is air tight and your gaskets are good and coolant cap and res is good. Bad cause there is air that needs out. Now back to sensor is loose u feel suction your starting to pull up. Go slow keeping it close to block. You will hear the air feel it and see coolant start to spit and steam out. Put sensor in and tighten it. I do this cause it seams to prime/pull the air out of block and suck coolant in faster to the head other than stressing the system longer at the tstat housing plug alone. Remember this was the only way to properly do this initially since these housings did not exist until later. The air stayes trapped in a closed system from water pump through block to head near firewall to tstat. So its like brakes bleed furthest point first. You can choose to repeat this process over and over untill just coolant comes out from start to finish while pulling the sensor. I typically will and never move the truck opposite direction nose up to bleed procedure from tstat housing. Reason being I will create more pockets making it take longer. U can though if its too hard of a reach or uncomfortable just know it takes longer. 1 thing though to remind u that between purges to top off lines and reservior. You must let the system cool between purges to do so for safety and boil over there is pressure so release cap slowly and know its gonna push coolant back out which is fine cause it will burp and fart and air pocket behind it and then fill. These systems suck because its a mess and there is no way around the coolant loss or mess. The cooldown process in between purges isnt long just a couple minutes enough to cool your near burnt hands to start again. You really could do it as fast as you want but the risk of getting burnt increases especially at the reservior. After you have burped the system and are satisfied with the results no more air its time for the double check. Now let your truck idal. Watch guage and close your heater valve. Shut off heat. Watch guage does it move? Does the engine start to idal different?  This has to be all done and observed at operating temp around 210. If nothing fluctuates good check again by turning heat on and to high. Observe watch guage listen to engine. If only minor fluctuations or a grunting engine under a slight load all could be signs of a little air. In this scenerio to purge park nose up and go about it at tstat with quicker easeier results top off ur done. If you get a climbing temp guage in any of your checks with heat contro or otherwise you still need to purge air. Now if you done this and done this till your blue in the face and notice that it only happens after a while with the heat heat on, start checking all over passenger floor board and feet area for moisture. If so bad news your heater core was what destroyed your last system and it won't work until u fix it and I'm done with my book.

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Or....you can test your water pump 

If you are 100% certain that you have the correct rotation pump on....there are reverse rotation pumps .....

Take the heater hose off of the water pump..

.put a chunk of scrap hose on it and please the end in a milk jug or pail....start the motor.....do you get a strong stream of water?

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10 hours ago, WahooSteeler said:

Yes, and just confirmed that again this evening. Put in a new tstat with "jiggle valve" and got it up to temp. Took a solid 15mins before temp got to 230ish, overflow bottle never budged, upper radiator hose cold to the touch. Shut it down and while looking around saw steady dripping at heater valve.  

Forgot to mention slightly critical item here.........when I changed out tstat I did not drain coolant and just pulled hoses from tstat housing expecting to lose some coolant but when I pulled them off there wasn't much coolant to speak of in the lines. 

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49 minutes ago, WahooSteeler said:

Pete, other than the obvious advantage are there any disadvantages? 

 

 

not that I've experienced.  it's the same radiator, but with a little tube sticking out and a rad cap on it.  In theory you should probably include an overflow bottle should the cap pop.  I just routed a hose down to the bottom of the engine bay.  

 

conveniently circled in this old pic. :D  

 

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3 hours ago, Pete M said:

 

not that I've experienced.  it's the same radiator, but with a little tube sticking out and a rad cap on it.  In theory you should probably include an overflow bottle should the cap pop.  I just routed a hose down to the bottom of the engine bay.  

 

conveniently circled in this old pic. :D  

 

Pete, what year and model MJ or XJ would I search for this replacement? Also, my truck has the factory HD cooling and trans cooler. I like the ability to easily do a flush with having the cap. So do you still have the pressure bottle on the passenger side firewall though and the hose off the cap is just a pop-off valve? 

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YXMJ, yeah, I think I'm resolved to getting one and converting to open system, eliminate heater valve etc. It seems that less is more with an open system, more consistent operating temps, easier to maintain/service. Came across a nice write-up in Four Wheeler mag from last summer where they converted an 89 XJ over and was essentially plug and play with new rad dropping right in etc. Being that I've already replaced all the mechanical components in the last couple of months it only makes sense to not only get a new rad as Hornbrod and others have suggested but to convert to an open system also. 

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