Highway speed overheat 89

I have searched and researched every thread on overheating XJ's and even posted myself. I have thought that my problem was gone a couple times but it always comes back. I have changed radiator, thermostat (oem with vent hole at 12 o'clock), lower hose from Napa w/spring, fan clutch, serpentine belt (routed correctly), water pump (it is the correct reverse rotation), pressure bottle from quadratech, cut bottom out of cat and emptied then rewelded, removed rubber alternator splash guard, converted to open system by installing cap in upper radiator hose and converting pressure bottle to overflow bottle ( making sure to block off heater hoses feeding bottle originally). I can drive around town with the a/c on and never start to overheat (gauge says about 200). On the highway though when running higher rpm's, the higher the quicker it happens, it will climb to 210 then keep climbing until I drop the rpm's to below 2000 and it will start to cool back down. It has not overheated for quite some time because I am always looking at the gauge but I feel like it would if I let it keep going. I don't know what to do next, I have 200k on this motor and it runs great still except for the cooling issue. It does look like it might have some mineral buildup around one of the freeze plugs which might suggest a minute leak, not enough to drip. No sign of coolant in oil or oil in coolant so I'm not suspecting head gasket. I plan to take the motor out this weekend and replace it with a 140k one from a friends wrecked 90 that was running fine. I will check radiator for flow again and install new freeze plugs in the new (to me) motor. I am planning to replace valve cover, oil pan, rear main,and distributor gaskets, though not related to cooling thought it might be worth a mention. I'm just fishing for any suggestions some of you wise Cherokee guys might throw out. I am planning to drive this thing to Colorado July 30 and would like to feel like it is right before leaving. Thanks!

Similar thing happened to my 89 - ok at idle but get hotter at highway speeds. Turned out to be the thermostat. It would not open all the way so the flow was restricted. I could see that the thermostat internal valve was rubbing against the body of thermostat. Perhaps your new t-stat or something internal to the motor or radiator is restricting the flow. Good Luck. Greg

same thing is happening to my 89.
it didnt start till i went to 4.88 with 33's, but 2500 rpm's is the magic number for me.
i didnt do the cooling conversion or the cat cut/empty/reweld.
i think im gonna stay under 2500, as i am approaching 200k.
i have a 180 t-stay with hole, and i have bled air of the system.

2500 rpm seems to be the hot spot for my rig also. It just seems to me that the cooling system should be able to handle 110 degree days towing a 1500 lb trailer up a 5 degree incline all day. I feel like there is something wrong and I just can't find it. Any possibility it might be timing related, possibly stretched timing chain or bad info being sent to the computer by some sensor or another. What about running lean due to a partially clogged injector or fuel pump. I do have correct fuel pressure at the fuel rail while idling. Anybody got any ideas? If so how to go about checking for them.

For anyone who is watching this thread, I have found a ton of fine debris in the lower radiator hose. The stuff in the hose looks like about a half cup of dirt was dropped into the cooling system. I found this by stretching a t-shirt over a five gallon bucket to work like a big coffee filter then taking the lower hose loose and letting it drain. Wow what a mess. I have flushed and filled several times prior to this. I used an acid flush yesturday to try to get the system clean. I'll post back with updates as I know more.

If you found that crud in the lower radiator hose I would then think long and hard about reuisng the radiator. I think I'd take it to the radiator shop. I am not sure if Woody's is still in business in Columbia. They were located just north of down town columbia off of 8th, 9th or 10th - been years since I've been to Columbia.

My Mom moved away in 1999 so have not been back since. My 88 XJ was purchased new in Jeff City and in 94 my parents purchased it used form a guy in Columbia. I got the XJ in 97 after my Dad passed away.

I would take the debris to the radiator shop and ask their opinion, I would either have the radiator flow checked OR get a replacement. Yes, I know you siad it new but the "dirt" you found may of fouled - plugged up - some of the tubes in the radiator.

I use to get tire and suspension work done at Shelby's tire and wheel, they are located at the corner of north College and the business loop, or the old Tandy "T".

Hope you get it all fixed.

I'm thinking the radiator might need to go, too. It seems to flow water fine from a hose, but just a few passages plugged would reduce effeciency, especially at higher flow rates........hummm! I hope this is the root of my problem, I will gladly spring for a new radiator to have a "cool" Jeep again. I like Schilby's also. Every time I have prices tires they have the best prices, besides that they are good to deal with. I like that. Thanks

An radiator shop can test the flow of the rad. to see if it's plugged as well. Usually the Jeep T-stats are pretty good quality. Does your electric fan work? Also I actually noticed a temp increase when I removed my rubber mat from the bottom of the engine compartment.

88 doing the same thing... saga continues

Seems mine's doing the same thing... overheated last week, been slowly rebuilding stuff all week as I got the parts. Flushed, new quadratec bottle, OEM thermostat / OEM upper+lower hoses. After pulling a instrument panel out of a 1990 since my temp gauge was gone, I did some test driving... took it up to 70mph, and it gets up to 240 degrees real quick. If I stay around 45-50mph it barely gets above 210. New fan clutch is going in tonight, since it seems real loose, but that shouldn't affect highway-speed temps, should it? Possible loose serpentine belt, would that affect it at highway speeds?

Of course, I'm still not sure the temp gauge is accurate... by the time I pull over to check the sender resistance the gauge's back to 210 degrees. Mechanical gauges I found at AutoZone all have fittings too big for the sender hole and no adapters to be found.