I would say try your heater control valve and if all else fails go for the all metal 3 core radiator from radiatorbarn.com

 

I drained ALL of the coolant, I figured since I was workin' on the cooling system I might as well flush it. So I bought some flushing fluid and followed the directions. it worked great.

 

Your are right, your auto was engineered to run at its best, for fuel economy and emissions at a certain temperature range thus the OEM temp thermos. But if your having problems with it overheating what better way of diagnosing the problem than changing the thermostat. It's cheap, easy, and solves a lot of problems. If the op has already changed it with a OEM temp. thermo and it still overheats what shall he do in the mean time? he may not have another vehicle to drive. Why not completely remove the thermostat (during the summer, or put in a lower temp one during winter - we still need heat don't we), so as to almost insure the vehicle will not overheat and still get him/her to work. But once all the problems are corrected, I would definitely put back in the OEM one, your jeep is made to run at that level; there are no performance gains with a lower or higher running temp.

OP...a clogged heater core can reduce the cooling effecieny. A good test for the heater core, is to buy one of the T's like you got from your flush kit, my autozne sells different sizes by themselves. Pop off the hoses going to and coming from the core, on the firewall, put on the T, leave the cap on and drive it around. I think you can guess the rest. If it doesn't over heat you have a clogged heater core, if it does overheat, and you have replaced all the other parts that you mentioned then I would assume is something clogging some water-jackets internally possibly. Just remember to do all the basics, including replacing the hose with the spring that was mentioned earlier, and burping her.
After replacing my cooling system, besides the heater core! hence my advice! I flushed the cooling system. I assumed it would be rather clean, I used the super cleaner from prstone that you leave in for a couple days, it worked great! it even unclogged my overflow hose and blew a chunk of nastiness into the overflow tank.

 

The heater core has nothing to do with the cooling system efficiency.

 

+1 its closed normally unless the heater control switch is not sealing

 

I beg to differ....why is it then, if its normally closed and fluid is not circulating until you pull the switch, the heater core can leak even when not turned on...magic?

"Anti-freeze is constantly being circulated throughout the engine, radiator, and yes even the heater core regardless of whether you have the heater dashboard switch on." http://www.trustmymechanic.com/newsletter4.html

 

Let me get this right.....If the heater core is not working correctly, not just clogged but say maybe even a hole, where air can get into the system and cause an air bubble, or so much crud inside the core that it is sending a blockage down the line to the thermo or waterpump...and OH! overheat...you don't think that has anything to do with cooling efficiency? I have to politely disagree. I have seen a leaking heater core that does not leak inside the cabin enough to tell where the problem was until we had the dash board off...for a completely different reason...it was allowing air to go into the system and get trapped in the motor where it would overheat. catching on to the theme? changed out the core and his truck no longer overheat.
Thanks anyways djb! you'll get it next time.

Come on man, don't give discouraging information if you can't explain your reasoning any better than 'no'.

I think you would agree, djb, running the heater hoses in a loop would eliminate any heater core issues, whether or not you believe it has anything to do with efficiency. And thus one more thing to cross off the list as probable causes to op's overheating probs.

Like I said originally....replace the water pump, you are only messing with silly stuff when concerning yourself with the core. Who needs heat now anyways, just loop it.

 

That part is a valve that cuts off fluid flow to and from the engine on all (I think) XJ's it is a vacuum and cable operated valve, which stops any coolant from entering the heater core

it can leak even with the valve closed, simply because its a valve, it doesnt magically suck all the coolant out of the heater core, fluid is still there which can leak out, its just static fluid not circulating

 

Well duh, you're talking about a LEAK in the cooling system......that just happens to be at the heater core, in your case. Is there anyone else out out there that does not understand that a leak, regardless of where it is located in the cooling system, will have a negative effect on cooling system efficiency????

You just proved that the heater core has NO effect on cooling system efficiency because, like you said, it can be looped/eliminated from the cooling system, with no loss in cooling system efficiency.

If you have a leaky rad hose, water pump, t-stat or radiator you must repair/replace any/all of those items because they are essential to cooling system efficiency. You can eliminate the heater core (leaky or not) because it's not essential to cooling system efficiency.

 

Total agreement.
That's why I say to loop it, to bypass any possible leaks while diagnosing.

I did however fail to mention the engine coolant drain plug, located on the drivers side toward the rear, I believe on I6. Is this something you would take out prior to flushing every time? I did it the first time I flushed but did not do it again during all the following flushes. any advice? maybe the OP could benefit from it as well...I haven't hear many ppl talk about it before.

 

This is the way I flushed our '98 XJ. Disconnect the top rad hose and the 3/4" heater hose at the t-stat cover. Remove t-stat cover, remove t-stat and replace t-stat cover. Disconnect the bottom rad hose at the water pump. I didn't touch the rad drain plug. Run water from a garden hose through the top rad hose. This will flush most of the loose stuff that's in the rad out through the bottom rad hose. Run water from the garden hose through the 3/4" heater hose. This will flush most of the loose stuff that's in the heater core out through the water pump. Run water from the garden hose through the 3/4" nipple on the t-stat cover (again, t-stat removed). This will flush most of the loose stuff from the cylinder head and engine block out through the water pump. Flushing the cooling system this way eliminates loose stuff from (the heater core/cylinder head/block) getting stuck/deposited in the radiator.

 

OK, I received my 3 core radiator from the Radiator Barn and installed it today. When draining the radiator that was in my XJ the coolant had some crud in it at the bottom so I pulled the thermostat and water pump. I backflushed the engine from the thermostat opening in the head and let the water run out of the water pump opening in the block. Flushed some crud out here and also flushed the heater core and got crud. All of this after being flushed at local shop. I got everything re-assembled and so far it is running around 195*whether @ idle or cuising speed. For now, it appears this has solved my problem. I want to thank all for the posts and ideas. They were all of great help.

 

First off I am glade that you got it fixed. In a month or two you may want to flush it agin. I know it's a pain, but why not.

Ok I have 94 motor for my 87xj. I know about the diffrents. There is a lot of junk in the coolant walls. How would you get it out? I can't hot tank it. I am going to use it. The head is still on it so I don't have to worry about water in the oil, But I just cant blast it with a hp washer. The housing and the water pump is off too. What should I do?

 

Thats great news! Gives me hope....I just really dont want to fool with the cooling system even though I know I need to.

 

I flushed mine originally with a quick flush from NAPA berore I replaced everything and still ran hot. Then I had it pressure checked and professionally flushed by a local shop and still ran hot. I was still able to flush out crud yesterday when new radiator was installed. I dont know but it may take multiple chemical flushes to clean cylinder walls. After the stress with mine i would suggest that even after chemical flushing that the thermostat and water pump be removed and back flush though the thermostat opening until only clean water flows from the waterpump opening. Also backflush the heater core and radiator if not replacing. Best of luck.