I recently overhauled the cooling system on my '89 XJ because I was tired of having to vigilantly monitor temps and engage fans or heater to mitigate over-heating. Within the past two weeks I have replaced every component of the cooling system.

It still overheats at highway speeds. It starts out fine with temps in the 200-210 range running nothing but the 2500cfm fan but after about 30 minutes it starts to creep up. My aux fan is set to 210º and I have a manual over-ride but that only slows the temp rise. Eventually, I have to turn the heater on (miserable when it's 100º outside) which lowers the temp slightly, for a minute or two before it again starts creeping towards that last hash mark before the red. It never actually overheats (like, steam and fluids escaping) but it gets very hot on flat ground under very little load. It seems to perform okay in stop and go traffic and, after exiting the freeway, the temperature will eventually return to normal. I live in a warm climate that rarely if ever sees freezing temperatures so, for now, I am running a 2:1 ratio of distilled water to coolant (2 gallons of water and 1 gallon of green coolant). I did not drill the thermostat and I filled through the expansion tank with the rear end raised.

Any ideas? I have replaced the:

Radiator (OPL 3-row aluminum)
Thermostat (Stant 195º)
Thermostat housing
Water pump (Flowkooler)
Mech fan ( Electric 2500cfm Flex-a-Lite puller)
Aux fan (Electric 1750cfm Flex-a-Lite puller)
Heater core
Heater valve assembly
Expansion tank (1st Dorman - OMG what a piece of crap, then NAPA)
15PSI Expansion tank cap (NAPA)
ALL hoses
Idler pulley
Reduced length serp belt to accommodate clutch fan delete.

The only part of the system that was reused was the small "Y" hard line that splits off of the heater core return (I think) because I couldn't find a new one. I did scrub the inside of the old one with a wire brush until all rust and contaminants were gone.

 

89 is a little out of my experience (I have a 96). I assume the transmission still cools through the radiator on a 89? If so, have you ruled out the possibility that it is the transmission that is driving the temperature up gradually? You may want to take some separate IR thermometer measurements of the thermostat housing as well as the transmission oil pan next time you can reproduce the symptoms to see if there is any alarming numbers there. If you have an automatic (I don't know what trans an 89 has), does it use a torque converter lock-up clutch like the AW4? Because a failure to lock-up (for example, a failing lock-up clutch solenoid in the trans) can cause the torque converter to get very hot at highway speeds (gradually).

Not trying to be a know it all, just considering possibilities.

 

Please don't be afraid to share your knowledge or theories, your advice is always excellent and thoughtful.

The 89 would have the AW4 if it's an auto or the AX15 (internal slave) if it's a manual (unless replaced/modded).

 

Head gasket failure?

 

This is definitely something to consider. It is an AW4, it does cool through the rad and I have been having issues with converter lock-up. I'm going to research forced torque converter lock-up and put a switch on it to test. I've been wanting to do the 1st gear lockout, anyway. Thank you for the suggestion.

 

Both oil and coolant are clean with no evidence of mixing. I have ordered a combustion gas detector and will confirm there isn't a leak, elsewhere.

 

Alright, I finally got around to testing the coolant. No combustion gasses present. I tested my old coolant as well and it also came back negative for combustion gasses. I have also confirmed that my torque converter is not locking. I recall (a couple years ago) there was some odd behavior. I would be driving across the desert at 75 or 80 mph and the transmission would seem to bounce in and out of overdrive even though I was maintaining a steady speed. I suspect that was a not-so-subtle message from my #3 solenoid. I've checked my brake switch adjustment and adjusted the TV cable but TC lockup is still MIA. A new set of solenoids arrived today, along with a filter, a gasket and four gallons of Dex/Merc - I plan on flushing the system several times. I also got a new headlight switch and the Azzy's transfer case linkage, neither of which will help with my engine temp issues, I'm just bragging. The temps have stabilized since my original post a couple weeks ago. There was likely air in the system, exacerbating the erratic temperature fluctuations. They seem happy to hover within a needle's width on either side of 210 and will only venture into the annoying zone after extended periods at highway speeds or on hills with the AC running. They do gradually return to normal when I get off the freeway.

I'll update you after I get the solenoids installed. I'm gonna install a 1st gear lockout switch and another switch that I won't connect but use for a TC lockup, if necessary.

I used the Lisle 75500 combustion gas leak detector from Summit. It cost around $30.

 

you can test your old coolant ?

 

Only because I still had it stored in a sealed Home Depot bucket waiting to be recycled.

 

Just finished an 1100 mile offroad trip in my 89 XJ. It was having the same overheating problems. After fighting with it for 4 days, had the hood up when it was dark out and noticed the #6 sparkplug wire was grounding to the head. This meant there was a unburnt fuel dumping passed the O2 sensor cause the engine to run lean. Got new plug wires in the next town and temps stayed under 210 the rest of the trip.

 

Nicely done on locating and fixing the problem and nicely done on the road trip. My plug wires are only a couple years old and carefully anchored away from the block/head.

I drove home, today (17 miles, a mixture of freeway and city) with the AC running and 87º ambient. Never went over 210. It seems the new hardware has settled in and decided to behave. I'll be swapping out the solenoids, filter and trans fluid this weekend. At the very least it will improve my fuel economy.

 

i tried to run 2 electric fans and was not able to pull it off ! the mechanical fan flows a lot more air so back to 1 electric and 1 engine drivin

 

Put the clutch fan back on and see how it does, many people delete the clutch fan and go all electric only to find that the e-fans don't pull enough air and they have overheating issues. In my opinion the best cooling setup for an XJ is a properly working factory setup, with the bigger fan clutch off of the 4cly XJ.

 

I'm not ready to give up on the e-fan, yet. As I said in my previous update, the temps have stabilized with the exception of long periods of time at higher speeds (above 80 mph). I replaced my solenoids, today and flushed the trans fluid. While it has yielded more positive up and down shifts, it did not resolve my TCC lock-up issue (it's still not locking). I have adjusted the TV kick-down cable, checked the brake switch adjustment. I'm not sure what else to do. Knowing that I have a good #3 solenoid, I'm going to install a lock-up switch for now.

 

Test the TCC switch.