For my next trick I like the missing air dam trick. It shouldn’t be a problem on the Cherokee because you have good airflow without it. It’s attached under the radiator and increases airflow though the radiator even though it serves other purposes. File this one in the Fin Boy folder for me.
But with all due respect… you’re not married to this Jeep. You don’t have to keep “living on the same city block”, to use your phrase.
I’m a to each his own kind of guy, to be sure. Your choice don’t affect me. But I have little or no tolerance in my life for a problematic older vehicle that drains my money and time, if I have another option.
Personally I’d have sent this one off into the great beyond well before now. But to each his own. 
If a repair shop damages your vehicle and is obligated to repair it to its prior condition, when do you release the shop from their responsibility?
It would have been less stressful to have the vehicle repaired at a more qualified repair shop.
Yeah, I am as cheap as the day is long, and even I would have cut my losses and sold this vehicle “as-is” for whatever I could get for it, once an engine rebuild was needed. Someone else, who is an enthusiast of this type of vehicle might be willing to spend the money and/or effort, but I am not that person.
I like to keep my cars at my own peril. Sometimes win, sometimes lose. I paid $10,000 for my olds diesel in 1981. Two years later the dealer offered $2000 in trade. I said no and drove it to 480,000 with several engines etc. bad move. I traded my riviera with 520,000 miles. Looking back i would have been money ahead selling it at 300,000. I usually get 100 to 200,000 with no significant issues but you never know.
Replacing the OHV head on this XJ is quite a bit simpler than others with an OHC. If I really liked it I’d search for a Jeep shop that probably has done this several times.
Wrong head gasket or a vacuum line leaking or misrouted.
Thank all of you for your input, expertise, and very valuable insight. I appreciate all of it. There are two persistent conditions remaining: misfires and heat spikes.
Root Cause
Still do not have this. My suspicions in order of my current belief are based on elimination (so many new parts and configuration changes with fans and radiators) :
A. PCM. I am considering a Mopar, or a rebuild, or an after market (I’ve read try to avoid third party).
B. Poorly burned fuel: Champion plugs, pigtails, poor design coil from factory or two third party coils, 91 ethanol fuel, quality of fuel (brand).
C. Air Circulation: I do not want my fan to come on at 218 F and am considering a pusher fan with an S blade. The three electric fans are being deleted with the single core aluminum radiator right now.
D. Coolant flow: I am considering a $40.00 Crown high flow thermostat housing.
E. Heat soak from the exhaust to the fuel rail so I am requesting an insulation kit for the fuel rail. This was a factory recall. The solution was to add silver insulation to the coil pack and the fuel rail.
F. Air bubbles. I need to make sure my Robert Shaw high flow thermostat has a hole at 12 o clock or have a hole drilled to allow the bubbles out of the system so coolant circulates.
G. I keep wondering about my heater core and I have asked for it to be bypassed more than three times. When it had a 160 thermostat in July, it was building heat fast on a flat road over 160 so if the thermostat was open I’m gathering coolant was using the hoses to the heater core. Maybe the heater core is blocked?
H. I keep wondering about the lower radiator hose that so many videos and forums insist on having a spring. So the spring goes bad and goes into the water pump so supposedly the lower hose was redesigned to never need a spring again and supposedly does not collapse in the middle of the hose causing overheating on acceleration. Why: this is overheating on acceleration going down a flat road with no load and no A/C.
I. Spark. I am having the Mercedes designed coil pack removed. Going with spark plug wires to replace the pig tails. Going with NGK V plugs instead of Champion. Going with RIPP coil pack for higher horse power and better spark. I am going with these for the misfire reasons to rule out that the misfires / poorly burned fuel may be causing the inferno.
Cycle
After the overheating at one shop, I suspect a lot of overheating honestly after a hole was put in my radiator, before they replaced the fan shroud and radiator; I believe an overheat cycle started that may be perpetual for some time. It has run hot since then. Always over 210 not like before when it stayed at 210 or below. I also currently believe that each overheat leads to more degrading and possible damage to other things under the hood.
Rebuilt
After the overheating began two and a half years ago, the cylinder sleeve came off one of the pistons not many miles later. I went to a machine shop. The L6 engine was removed, disassembled, a new camshaft was put in, a new piston was put in, and while the head was off it was magnaflux tested and passed. The head was not warped and did not need to be milled.
Misfires
After the rebuild, my Iridium plugs had changed to Champion plugs and misfires occurred on many different cylinders usually one at a time. Usually cyl 3, 4, 6. I can’t recall 1, 2, or 5. Injectors and plugs have been interchanged to see if the problem continues plus two BG induction treatments. All of the injectors were replaced about two year ago. The spark plugs and coil was replaced about two ago. The misfires continue. The shop says they occur at cold temps. My experience with them is the misfires only occur after 210 F temps with or without mini spikes. The mini spikes are the worst if temps are over 90 outside. All of us do not know why the misfires are continuing. I read one forum suggesting the cause was 91 high octane ethanol fuel. So if I get it back to drive it again I am going to use 85 ethanol or 88 ethanol free specific brands and track misfires and heat to see what happens. I have almost zero confidence this is why.
New head
I decided the head should be inspected further for cracks, and it was removed, magnaflux tested again and passed and no cracks were found between cyl 3 and cyl 4. No cracks anywhere. The head could be re used if anyone wanted a 0331. While off, a new head was ordered because it was the 2001 stock head and not 2002 TUPY.
No joy
A test drive produced the same reproduced results. With a high flow thermostat, a high flow water pump, all new hoses, new head, new camshaft, sixth radiator and cap, electric fans with one of three turning on at 218 F.
Hail Mary
So the sixth new radiator in two years is being pulled. For a dual core radiator, new fan shroud, heavy duty fan clutch (maybe a Grand Cherokee? or a Murray?) with factory fan (or maybe a Taurus fan?). There is a belief that going back to pure stock radiator with fans and fan clutch will solve the heat spikes.
The electric fan should switch on at 223 F, and off at 217 F. That is normal and is not an overheat condition. They all operate this way without fault.
Does the engine overheat? Are you still losing a gallon of coolant every 3,000 miles?
If too aggressive cleaning disk was used to clean the gasket material off the engine block. A uneven surface could have been created and the head gasket wouldn’t seal. Might only happen when the engine is warm but th3 block would be ruined..
??? That does not seem to be the problem. I would have bailed on this vehicle or put it in a shop for a crate engine and drove it for as long as possible.
I would find a better shop. This isn’t rocket science.
Thank you Nevada_545 I appreciate your reply and everyone’s input.
The shop found no oil in coolant and no coolant in oil. No steam cleaned spark plugs or cylinders. No white smoke in the exhaust. The explanation of lost coolant in the previous two oil changes was leaking past one to four hose leaks. I have not driven it since June so I don’t know yet.
My personal take on the coolant is: the radiator cap on the single core aluminum radiator isn’t working right. One of the forums discussed a bad radiator cap can cause coolant to blow out the hose clamps. Why sell a radiator if the radiator cap is garbage?
I am letting go and the shop is letting go of the radiator plus fan set with 25 amp fuse. That setup should not be on the market. Three electric fans with a 25 amp fuse are inadequate; Going factory.
No, sadly the new head did not solve the past 220 to check gauges heat spike condition.
Changing it did give peace of mind the 2001 head won’t crack later.
Radiator caps rarely go past their pressure rating; instead, they usually fail by losing pressure or getting stuck open rather than over-pressurizing. If your various hoses are 25 years old, that is more likely the culprit.
Early you stated there was one radiator that was your favorite, why not get the same brand/part number?
I’ve encountered a few pressure caps that didn’t open, which led to problems
But I’m a long-time professional mechanic, so my sample size is substantial
How often does this occur during a ten-mile drive? How many seconds or minutes between 250 degree spikes?
During a ten mile drive in 70 F nothing happens.
During a ten mile drive over 90 F outside the temps climb when the wind from driving it should be cooling it and will be 220 and then the third fan comes on. The engine has to be turned off and hood opened to allow the fans with the key on to rapidly bring the temp down. As fast as it spikes over 210 F it comes back to 210 F in under a minute.
Over 90 F outside in particular, driving up a hill all the way to a destination ten min away, it will be warmer than it should and AC turned off to not give too much load. At the top of the hill the temp leaps from 210 F to check gauges. 235 240 maybe hotter. Have to turn it off. Open hood. Key on with three fans to correct temp.
Going up a mountain pass with the AC off the outside temp drops up to 20 F down near 70 F outside. But without AC to keep the engine temp reasonable it cannot reach the summit without having to stop due to a temp spike. Cool off 1 min. Back to 210 F.
It’s almost as if the temp spike is a who knows one cylinder not firing allowing fuel to build up and then all the sudden a ball of fire super heated causing the temp to spike. Not the whole engine. How could a whole engine change from 240 to 210 in less than a min or clime in less than a min.
Meanwhile the temp of the driver is just as fried without AC in the summer trying to keep the temp lower under the hood. Reducing load without AC.
Mid summer, in a parking lot, with the hood up, the AC can run and temp is a little over 210 F. Drop the hood to closed will instantly spike it to whatever throws check gages. 240 F? Have to turn it off, open the hood with the key on, for three fans to bring the temp back down.
The correction in temp seemed unbelievable to me so I brought it in for an oil change explaining the temp spikes saying I did not believe the gauge. It was reproduced and verified with a heat gun. Haven’t driven it all summer since.
The shop tried a 160 thermostat and it went well over 160 without load on a straight level highway without AC. Also does not make sense. Supposedly one does not even need working fans on the highway.
It’s almost like all the fans are blowing the wrong direction but they aren’t. Or maybe like the coolant is not cycling due to air bubbles but I know they’ve burped it so many times. Or almost like the pressurized coolant to keep it from being too hot just for a moment loses pressure but re pressurizes like a crack expands at high temp over 210 and depressurizes the coolant system. This is why we zeroed in on the head.
These are custom installed fans, are they blowing in the correct direction? Are there two fans behind the radiator and one in front? Are they blowing against each other? I have seen vehicles with fans blowing forward, engine runs hot while driving, cools when stopped.
If the cooling system was found to be one gallon low during oil changes, you were operating the engine dangerously low on coolant.
You need to check the coolant level before driving. If the engine is running hot, how do you know the cooling system isn’t 3 quarts low?
To add to Nevada, check the coolant in the radiator, not just the overflow tank. Nevada’s comment on the possibility of the fans working opposite of each other is valid. Or are the three fans actually blocking airflow? Please post pictures.
That sounds like a sensor or gauge problem. Get a good quality infrared thermometer and record temperatures at several points on the cooling system when it’s showing 210 and when it’s showing 240, see if temperatures actually increase.
Nothing to do with one cylinder not firing, you’d feel a big stumble.