87 cooling problem, keep blowing bottles

Specs are as follows

87 xj
4.0
aw4
engine completely stock

The truck runs fine on the street to and from work but when i hit the trails the temp slowly rises to the red, i stop and let it cool down but at theat temp the bottle gets fairly bloated and more often then not springs a large leak. I have used ducttape and river water to gt me to the trail head the last time. I have replaced the bottle, cap, fan shroud, clutch fan. I have also changed the waterpump to an autozone pump. My question is first if anyone has any ideas why im overheating. Another question is why is there so much pressure causing my bottle to burst. Did i buy a pump that flows coolant in the wrong direction?? Has anyone ever heard of that before. Anywho im stumped. All Help would be appreciated

-Mike

im pretty sure i did. I dont know of any real way to bleed the air out so i squeezed some hoses ect and then i had this stupid idea to blow inside the bottle and a bunch of air came out and all the coolant finally ran into the system. I dont know if that bled it or not, i cant seem to find a bleeder valve or anything.

-mike

loosen the temp sensor in the back right of the engine block. with out the motor running!!! http://www.olypen.com/craigh/cooling.htm

Never having owned one of the closed systems I can only go by what I have read, heard and experienced from friends who do have them.
To fill the system top the coolant off thru the rear temp sender on the back of the head with the back of the jeep elevated. Then put the sender back in.
The only thing I see missing from the replacment list is the radiator, they do go.
The thermostat is probably shot even though it's new, only takes one overheat to toast a tstat.. make sure it has the bleed hole in it too, hole goes to the 12 O clock position.
As for the plastic tank, also called a surge tank, I personall would not use a plastic one, I'd get one of the alumium or brass/copper steel ones that takes a normal radiator cap. With one of those you can actually put in a real overflow tank...

I dont know if there is a radiator pressure tester out there that can screw on to a renix xj waterbottle??? Thats what you need though to see if there are any pinhole leaks in your cooling system. It needs pressure to keep the water from boiling....I guess, if I were you, I'd probably go ahead and change it to a later model radiator, throw away the heater valve thingy and run straight hoses from the heater coor to the motor...that should eliminate a lot of your potential leak sights

I dont think that they could find a pump that would pump in the wrong direction...

also is the transmission in good shape? I've had transmissions that were going bad heat uf the ATF alot when used hard off road, causing the coolant to warm up...

Good idea check that Radiator. I just left the cap off while ran the engine I could see the air comming out of the coolent ran it till I saw no more air shut her off and replaced the cap, It has never over heated. Thats after I replaced the Radiator and all hoses.

sound like the radiator. If it is original. Also is the Aux fan coming on when you get hot? should do if you are running that hot.

That article helped quite a bit. Thanks

i Will bleed the air out when i get home and im just gonna take the tstat out until im satisfied that this problem is solved. The radiator is 2 years old but it is the plastic tank type so im thinking it might be clogged. The mechanic at work told me of a hot cold test for the radiator as in hot on the top and cold at the bottom or something like that. And i think the tranny is in good shape. It has 242k on it but it shifts smooth and has no clunnking. I change the fluid in it every 30k. May have to get a tranny cooler. The only thing i dont want to do is bandaid the crap out of the system. I just want it to work like it was supposed to work.

thanks guys
-mike

oh yah...on renix xj's you can wire the fan to run full time by finding the sending unit in the driverside back of the radiator, finding the electrical connector for it under the snout of the air box, you can unplug the sensor and jumper those two wires together...should make the fan come on whenever the key is turned on...

The fan comes on at 225 right now but i def want it on all the time i live in arizona gets hot out here

thanks dude

I had overheating problems on my 87 XJ spewing fluid out the bottle and bursting lids. I replaced the Radiator with a brand new one and I run 180-190 all the time, haven't had a heating/cooling issue since.

A partially pluged radiator will give you all sorts of grief. Filling the surge tank to about 1/4 when cold, gives things some room to expand and seems to help save wear and tear on the plastic tanks. I've been thinking of going to a metal surge tank, but actually like being able to see the fluid level through the plastic tank. I'll probably find a sturdier replacement plastic tank some day with compatable inlet and outlet sizes, no luck so far.
I found a handy spot near the thermo switch on the lower left rear of the radiator and used two blind end splices to run two wires back into the dash and installed a switch. I turn the fan on before I idle it long or run at low speeds for extended periods (or when towing).
There seems to be a fairly fine line between when the thermo switch turns on the aux fan and when the coolant boils and spews out the surge tank cap on occasion. I turn on the aux fan before it gets very hot.
Since I've switched to the themrostat with the bleeder hole, the system seems to purge itself of air pretty quickly and I haven't had any boil overs from trapped air.
There is a reverse rotation water pump, that looks like it will fit the 4.0 (I never got that far, I spotted the flaw, before trying to install it). I'm not sure wether it was a rebuliding flaw (it was a rebuild) or designed for another Jeep motor. It won't pump in reverse or build excess pressure. It pumps in the same direction, but poorly, from what I've heard. it is a cyntrifigal pump, and will pump in the same direction, but the impeller fins are oriented in the opposite direction so it works poorly. Or so I've heard from people who say they have actually installed one.

Scrap the plastic OEM thingy and go to Mac's Radiator and order the aluminum one's they make. I've had one on my 90 Laredo for 2 years now and works great about a 100 bucks....