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I am pretty frustrated :headpop: . I get the jeep lifted and I can't make it 3 miles without overheating. I would like to know what it took to get your overheating issues cured.

 

What I have done to my 89 Renix 4.0:

I have replaced the thermostat,

Top hoses,

Serpentine belt,

Temperature sensor for the electric fan (still doesn't work - have it bypassed with a switch),

Temperature sending unit on the block,

Changed the fan clutch,

Thermostat and added two small holes in the thermostat per 5-90 on NAXJA,

The bottle and cap with what looks like a newer design.

 

I burped the system as best I could by jacking the rear end up as high as the jack stands could go. Ran the jeep until hot. Then I removed the temperature sending unit on the block to let out the air and to add more fluid – not needed. How many times do I need to perform this stunt to be sure the block has been burped?

 

History –

The jeep never ran “cool” but was always within the safe zone and this was without the electric fan. It wasn’t until I changed the thermostat (without holes) and bottle that the real overheating began. I thought it maybe it was the cap on the bottle, so I added a hose clamp to it - no more leaking but still overheats.

 

Today, after I added the improvements (new hoses, modified thermostat, fan clutch, and belt) I burped the system and went for a drive. The thing starts to heat up with the electric fan on. I pull over and turn it off to let her cool down. I get back in and it won’t start - not even a click? Pop the hood wait ten minutes and it starts - is this just because the starter is over heated?

 

My questions are - Is it time for a new radiator? Could it be the new thermostat? Should I stay with the closed system, or go to the open system? Help - Rich

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Hi Rich,

 

I too have a 89 Comanche. Had the overheating problems too. I also did the same thing with the hose clamp on the bottle cap. After two new plastic bottles I searched for something better and found this.

 

http://www.macsradiator.com/replacmentj ... tanks.aspx

 

I don't know if it will solve your problem, but at least you will know its not the bottle. Plus this tank will allow you to convert to an open system if you want to.

 

Good luck :cheers:

 

Dave

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It sounds like the only thing left is the radiator unless you have a clog in the heater core. Did you try hooking a hose up and flusing the heater core both ways? or I believe you can connect the hoses without going into the firewall (bypassing the heater core) and see if it overheats. If it doesnt you will know the problem is probally a clog in the heater core. I am not sure how to do this so hopefully someone else will chime in but I remember reading a thread where someone did this because they didny need heat and the core was bad.

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A radiator is a good idea. I put in a new radiator that I bought from summit racing. It took me a while to stop the trans fluid leak. The fitting on the top needed to be tightened. While I was in there I noticed the water pump was leaking. I changed it. The cooler lines were toast, I changed them too. And the fittings in the trans. I didn't want any leaks there. New thermostat, upper and lower hoses, fresh coolant. I also replaced the switch in the radiator and it works fine. The temp starts to climb in traffic, and the fan kicks on and the temp drops, just like it should.

Good luck with yours.

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I am pretty frustrated :headpop: . I get the jeep lifted and I can't make it 3 miles without overheating. I would like to know what it took to get your overheating issues cured.

 

What I have done to my 89 Renix 4.0:

I have replaced the thermostat,

Top hoses,

Serpentine belt,

Temperature sensor for the electric fan (still doesn't work - have it bypassed with a switch),

Temperature sending unit on the block,

Changed the fan clutch,

Thermostat and added two small holes in the thermostat per 5-90 on NAXJA,

The bottle and cap with what looks like a newer design.

 

I burped the system as best I could by jacking the rear end up as high as the jack stands could go. Ran the jeep until hot. Then I removed the temperature sending unit on the block to let out the air and to add more fluid – not needed. How many times do I need to perform this stunt to be sure the block has been burped?

 

History –

The jeep never ran “cool” but was always within the safe zone and this was without the electric fan. It wasn’t until I changed the thermostat (without holes) and bottle that the real overheating began. I thought it maybe it was the cap on the bottle, so I added a hose clamp to it - no more leaking but still overheats.

 

Today, after I added the improvements (new hoses, modified thermostat, fan clutch, and belt) I burped the system and went for a drive. The thing starts to heat up with the electric fan on. I pull over and turn it off to let her cool down. I get back in and it won’t start - not even a click? Pop the hood wait ten minutes and it starts - is this just because the starter is over heated?

 

My questions are - Is it time for a new radiator? Could it be the new thermostat? Should I stay with the closed system, or go to the open system? Help - Rich

 

I went through this whole drill a couple of years ago, including a new rad, nothing helped. Found the problem when upgrading the exhaust - the cat was just about clogged shut. Bypassed it - no more overheating. Worth a shot.

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I went through very similar problems with my Dodge Dakota a few years ago. Replaced just about everything there was to, water pump, therm,hoses etc: except the Radiator. Turns out the PO must have put some tap water in the coolant which eventually led to plugging of most of the cores in the Rad. It looked fine on the outside, and everything was clean but the radiator was basically toast. Once I replaced it everything was back to normal. I would try that next.

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Where did the t-stat come from? Be very, very sure it is for a 4.0 and NOT a 4.2. The 4.2 is similar and will appear to fit just fine, but the 4.2 stat is just a tad longer and will bind on the 4.0 t-stat housing when tightened, not allowing it to open. The way to tell is the 4.2 stat is rounded where it goes in to the housing, and the 4.0 is pointed.

 

(don't ask how I know this :wall: )

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Rich, I'm having a similar problem.

I don't overheat but I am running hotter than the advertised 210*.

I also did everything you did except I bought the metal tank to replace my plastic tank and basically converted it to an open system by adding an overflow bottle. I'm still running "hot" (215*-220*) at the the thermostat housing. My radiator looks newer and I had the system flushed twice at Valvoline. I'm thinking that there is still a blockage in the rad so I ordered a new one from MotionOffroad. It's supposed to be here this week so I'll let you know if it works.

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I am about to start researching this as well. While my truck has never overheated on me, it bounces between 210 and 225 consistantly. It never seems to stay high, but every now and then it shoots up there and then cools back down. I might just start with a nice radiator flush.

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Thank's for all the replies. I broke down and ordered a new CSF radiator. I may even end up getting that aluminium bottle too PIKE. Chico is that the same one you bought? And what do you think of it - worth the money?

 

I can't believe that the Caddilac converter caused your overheating Hornbrod :nuts: . Mine was MIA when I got it. Must have been a drawn out process to solve that one.

 

Aemsee, all I can say is that I hope it is the right one :eek: . If I am still having problems after the new rad, I will be replacing it with a OEM thermostat.

 

Good luck to everyone in the same boat and Thanks again for all the replies - Rich

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Yep, same one. I got the idea from Eagle and the website from PIKE. It's worth the money to me because I bought three plastic bottles from dealers and all the caps' thread went to crap causing the system to not be under pressure and having coolant blow out the top. I'll never have that problem again. I also bought a CSF rad from Motion and am waiting for it to arrive. Hopefully it solves my problem. However, you could save some money and do away with the expansion tank altogether and get the radiator for 91 and up that has the filler neck. It doesn't have a bung for the fan switch but it doesn't matter for you because you're already running the aux fan on a seperate switch. I spent the extra money for the metal expansion tank because I wanted it to stay as stock as possible. I just posted pics of my tank in the MJ projects section if you want to see.

Keep us updated will ya?

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Yep, same one. I got the idea from Eagle and the website from PIKE. It's worth the money to me because I bought three plastic bottles from dealers and all the caps' thread went to crap causing the system to not be under pressure and having coolant blow out the top. I'll never have that problem again. I also bought a CSF rad from Motion and am waiting for it to arrive. Hopefully it solves my problem. However, you could save some money and do away with the expansion tank altogether and get the radiator for 91 and up that has the filler neck. It doesn't have a bung for the fan switch but it doesn't matter for you because you're already running the aux fan on a seperate switch. I spent the extra money for the metal expansion tank because I wanted it to stay as stock as possible. I just posted pics of my tank in the MJ projects section if you want to see.

Keep us updated will ya?

I just checked out both of your pictures. Dayem, those are nice looking! I am going to go back and read through them because I can't figure out the need for the overflow bottle? I am going to call them in the morning and order one.

I went with the closed CSF radiator because the guy at ??? told me that the open were on back order. He also said that CSF was going to discontinue production on those and pursue making the plastic end radiators ( they cost 40% less to make). He did have the closed unit in stock - imagine that. I ended up getting it at Radiator Barn, we will see how that works out. Much respect to you and PIKE for the clean install - Rich

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By adding the plastic overflow bottle by the air cleaner I made it an "open" system. I can now fill the metal expansion tank to the top and the fluid runs to the the plastic one when it heats up and expands and then gets sucked back in when it cools down. I guess the other advantage is I now have more fluid in the system and I don't have to worry about bleeding the air out of the closed system anymore.

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I can't believe that the Caddilac converter caused your overheating Hornbrod :nuts: . Mine was MIA when I got it. Must have been a drawn out process to solve that one.

 

Well, at least I got a new cooling system out of it before I found out it was the cat all along. :D BTW, some of the closed system rads do have the bung for the temp sensor. Below is the aluminum rad I use and the bung is highlighted.

 

 

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Curious question?This is my first MJ and I yet to change out the idiot lights for manual gauges.When I do what temp should my engine run at?

 

Also what to say thanks to everyone for the great threads and info recently joine and this place jamminz.gif

 

It depends what temp thermostat you have. I believe the oem thermostat is 195*

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would it be safe to change to a 180 stat?thats what Ive run in my SBC for years just not to up to date on these jeep engines.I'm fixing to flush and flush and repeat ect. the PO that I got it from was not maintinence friendly,but his PO kept records in the origianal Owners man. and was pretty faithful to spec.265k and does use 1/2 aquart every other oil change ne way sorry to get off topic. -T.J.-

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Curious question?This is my first MJ and I yet to change out the idiot lights for manual gauges.When I do what temp should my engine run at?

 

Also what to say thanks to everyone for the great threads and info recently joine and this place jamminz.gif

It should run at 210+/-, but usualy + a little ;) . Mine tyically runs a bit under that, but I have converted to an open system and run a 3 row radiator. It does get up to 210 on the 95* days with the AC running occaisionally though ;)

 

Covington, LA ... Are you a friend of Jake's? Glad to have you in the Club, and yes...you will enjoy it here. Great people!!

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Pike is right about the high concentration of anti freeze. Water is a better carrier of heat than coolant. But the reason I chimed in is I recently removed the heater control valve from the hoses leading to the heater core and noticed and big difference in the temp gauge. I looked into the control valve after I removed it and it is a huge restriction in the coolant flow. And yes I did make sure the valve was open when I looked through it.

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Pike is right about the high concentration of anti freeze. Water is a better carrier of heat than coolant. But the reason I chimed in is I recently removed the heater control valve from the hoses leading to the heater core and noticed and big difference in the temp gauge. I looked into the control valve after I removed it and it is a huge restriction in the coolant flow. And yes I did make sure the valve was open when I looked through it.

 

Yes, I've done this also. The main reason you can get possible lower engine operating temps is because w/o the water control valve, all the coolant to and from the heater core is under constant circulation, adding more coolant to the system. The constant flow through the core also helps to keep it clean and clog-free. With the valve in, the only time there is coolant flow through the heater core is when the heat is turned on and the valve opens. :D

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would it be safe to change to a 180 stat?thats what Ive run in my SBC for years just not to up to date on these jeep engines.I'm fixing to flush and flush and repeat ect. the PO that I got it from was not maintinence friendly,but his PO kept records in the origianal Owners man. and was pretty faithful to spec.265k and does use 1/2 aquart every other oil change ne way sorry to get off topic. -T.J.-

It's a misconception to think that a lower temperature thermostat will make an overheating vehicle magically run cool. The purpose of the thermostat is to keep the temperature UP, not down. Assuming a stock 195-degree thermostat, if your radiator is not capable of keeping the temperature down to 195 degrees, there is no reason to think it would be capable of keeping the temperature down to 180 degrees.

 

The bottom line is, when it's time for a radiator, it's time for a radiator ... anything else is a Band-Aid.

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