Overheating on highway only.... PLEASE HELP!

I have an 89XJ. I have been through all the trials and tribulations with the Renix system and the closed cooling system. So heres the problem

My water pump went out. Water pump changed with rebuilt water pump, metal impellars. New thermostat installed (dealer bought) and new pressure cap and expansion tank. No leaks in radiator and no leaks at my water pump and thermostat housing gaskets. I put Permatex on both and let set for 24hrs to esure a good set. Also, I do have the spring hose that does not colapse. Also I put a new belt on while I had everything apart.

Now, after doing all of this it will run fine if I am just putting around town at 35, which isnt bad being Nevada and 95 to 100 out. BUT, as soon as I get on the highway after about 10 to 20 miles she starts to creep over 210 and never cyles down below it. I know I am getting flow because I can watch it throwing just as much if not more water than the last (original) water pump.

Does anyone have any ideas???? If I cant figure it out I am about at the end of my rope and will probably put her out to pasture. Which would be ashame and I really dont want to.

Thanks everyone!

This is probably no help to you but I have a 1996 and my Dad has 3 1996s that all run over 210 in Wisconsin. I've tried a 195 thermostat also. I will watch this post for any good ideas. Good luck.

X2 - It is normal to run at 210. The factory efan on a 2000 doesn't even turn on until 223F and then turns off at 217F. Unless it's boiling over, you are not overheating. Sounds to me like you're good to go!

Searched google for more info. This says that antifreeze 50/50 won't boil until 268F with a 14-16PSI rad cap. Running 70% antifreexe gets another 12 degrees or so. http://auto.howstuffworks.com/cooling-system3.htm

Had the same problem on my 91, clogged radiator. A flush did no good, I could see good flow, fan clutch was new, I put in a new water pump, thermostat, pressure tested the system and it would still overheat on the highway. A radiator acts like a big filter screen catching all that crap for 20 years or so. Replace it if it is more than 5 years old. I would also ditch the football and convert to a 91+ cooling system.

Check the fan clutch before you put her out to pasture. I had the exact same issue that started a few months ago: fine at low speeds and started to run hot at freeway speeds - new fan clutch solved the problem. When they wear out, they don't turn fast enough at high speeds and don't draw enough air thru the radiator.

Im not thinking it is the fan clutch since one... it is pretty stiff if I try to move the fan by hand and two..... the problem in particular didnt start until the new parts were put on. Never had this problem before. What are the odds that the fan clutch would decide to go out with that kind of timing. Although dont take it the wrong way. I wont rule it out. Thanks for your input, it is much appreciated.

Seems like fan clutch would affect it more at slow speeds. On the highway, you shouldn't even need a fan.

Well, the key to cooling is heat exchange, and that happens for the most at the radiator.

So, why isn't your XJ cooling at highway speeds?

Could be the spaces between your tubes and fins is filled with debris, reducing air flow. Have you really checked?

How is your fan clutch? Both standard and ZJ HD fan clutches are engaged when the air flow hitting the bi-metal springs is about 170 degrees, and that is about 30 degrees less than the coolant temp. The standard fan clutch when engaged rotates at about 60-70 percent of shaft speed, the ZJ HD fan clutch gets you 80-90 percent--moves one hell of a lot more air. If your fan clutch is leaking silicone fluid the lockup may not be as complete and it may not be delivering your 60-70 percent.

Water pump and fan clutch are about maxed out at 5 years. When was your fan clutch last changed?

On the '89, it's sometimes hard to get the cooling system completely full of water. That's why Jeep changed to a more conventional system (sometime after '90). What I did was install a bleeder in the left (driver side) tank of the radiator. I drilled a hole in the top of the tank and installed a threaded pop rivet in it. I cut a groove in the side of a screw that fits the pop rivet (use brass so you don't get rust) and screwed it in the rivet. Now if I change coolant or something else happens where plastic surge tank gets empty, I refill and screw the slotted screw out enough to let the air out. I bleed the system several times (on different days) before I can be sure there's no air left in the system. You can even bleed it when it's hot. I had to make a hole in the plate above the radiator so I can access the screw with a screwdriver. It works great!