So I just had to cut a trip short due to overheating issues.

No issues on interstate going 65+ mph at 2-3000 rpm.

No issues going downhill on trails or cruising across mostly flat terrain at low speeds between 1-1500 rpm.

But after about 20 minutes of climbing any steep incline my temp gauge skyrockets from just over 210 up to almost 260 and I have to pull over.

When I pull over the coolant in my reservoir is bubbling/boiling like crazy. I let it sit for about 15-20 minutes and it will go for another 20 minutes of climbing before it jumps again and I have to pull over. This only happens when climbing up though. Once I reach a summit and head back down there are no issues at all and the temp stays at around 210.

I’ve turned on the AC even though I don’t have AC to make sure the secondary fan is kicking on and that doesn’t help. The coolant is being pulled from the reservoir, I can tell because the new coolant I put in the reservoir is being cycled through and is boiling off. I went through 2 full things of coolant over the course of a very long day just trying to get to camp.

The issue first started two weeks ago when I took a test drive in prep for this trip, got to the trailhead and it was over heating. Pulled over and the upper pressure hose that goes from the top of the reservoir to the radiator cap had come loose and clipped my fan ripping a hole. I got it wrapped up, made it back to an auto parts store and replaced the hose.

Drove around town and to and from work all the next week no issues. Drove out to the trail to attempt another test drive, got to the trailhead again and started to overheat again. This time no leaks or holes in hoses, just simple overheating. The drive to the trailhead is all interstate, then about 3 miles of switchback and climbing in elevation. It overheated as soon as I got to the trail head. Replaced the thermostat because I thought that could be the issue, drove for another week just fine. Drove 5 hours on Friday to my first campsite no issues. Second day lots of incline and elevation gain, a 2 1/2 hour trail took me almost 6 hours because of all the stopping.

Where do I begin?

2001 XJ
6.5” lift
No issues driving around town or interstates. Only after climbing, and when climbing it’s in 4 Lo, 3 or 1-2, and I’m keeping the RPMs low so I don’t think I’m overworking the engine and it never has problems as far as driving. Just overheating.

 

How old is your radiator cap? Hearing about the boiling in your overflow bottle leads me to think maybe the system isn't holding the 16lbs pressure it needs to which is controlled by the radiator cap.

 

Good call.
Engine is working harder to go uphill, so I have to guess its going to get hotter...
So either the cap isn't up to par, or the system has just enough circulation during normal driving instances, but going uphill and getting hotter, it isn't circulation enough.

 

I cant say I’ve replaced the radiator cap the whole time I’ve owned the Jeep, approx 60k miles. But it’s tight on there and it’s a SOB to get off whenever I need to check the levels in the radiator so feel like it’s doing it’s job well.

 

So what can be done to improve circulation? Would it be time for a new radiator maybe? Would a radiator system flush possibly help improve flow?

 

Usual questions.
Running the shroud around the mechanical fan?
What shape is your fan clutch in?
When hot and you shut it off does the fan spin for awhile or stop within a second or two/
If the first sounds like you need a new fan clutch.
Just replace the radiator cap anyway.

 

Cooling fan operation (or lack thereof) should be largely irrelevant at highway speeds.

 

Have you verified that the secondary electric fan is actually spinning when you select AC to try to force it on? Mine was behaving much like you describe and I found that my electric fan was never coming on.

 

I was having the same problem and did three things, but can't confirm which of the three things was the actual fix. Fortunately, all of them are pretty cheap. I replaced the fan clutch with the ZJ clutch. About 40 bucks from NAPA. I made sure that the thermostat had the detent or hole positioned at the top in the housing. This helps with burping the system and eliminate air pockets. And I replaced the lower radiator hose with one that has a spring in it and made sure it was not pinched. I had replaced the lower radiator hose with an aftermarket that did not have the spring in it and it would pinch against the power steering lines because it was not a perfect fit. I pulled out the original stock hose that fortunately I saved and re-installed that, making sure that it cleared the ps lines. I had to cut off about 1/2 inch off the end that fits to the water pump housing to allow extra clearance.

I was having the exact same problem you were and these three things completely fixed it. I can climb mountain passes all day long at speed without overheating issues now. Like I said, I don't know which of these things was the actual fix, but I suspect the lower radiator hose primarily was not allowing enough of the cooled fluid to pass back into the engine.

I also did an engine block test to make sure my head gasket wasn't bad. You can get a loaner tool from the auto parts store, but have to buy the test fluid for about 10 bucks. Some people also say to do a compression test, but I never got to that point.

 

I have a raging clue. The Rad Cap should not be super tight. It's a push lock design. Perhaps that tightness is a sign of a failed cap that is stuck in the open position. Either way, it sounds like you need a new rad and cap. Flush her out with the old garden hose while your at it.

 

I had a very similar problem, I never imagined that the fan clutch would have much effect with highway driving at all. I had changed my rad, thermostat, water pump and ensured the electric was functioning as it should. My 92 would be fine in 100 degree city driving but heat up badly on highway inclines. I finally changed the fan clutch and all heat problems resolved.

 

I've had Blue Devil coolant flush recommended several times. But they all do about the same thing.
Water pump provides the circulation of the system, so you may have to pull that off to check the impeller fins.
Radiator flush may or may not help, just depends on how dirty or NOT dirty the system is.

I'd start with the easy cheap stuff first. New cap, then check the fan clutch (when the engine is off and cold, spin the fan. It should stop very quickly after you give it a good spin, like a Wheel of Fortune spin. If it continues to spin like a ceiling fan, then its shot and needs to be replaced. Like Ralph said, it should stop within a couples of seconds after the driving force is removed i.e. engine or your hand.)
Feel free to do a system flush as well if you have the time. It can take an hour or two, depending on how much you let it run and all that. Taking it for a drive around town for 20 minutes can really help flush out the gunk. And search for "reverse flow coolant flush" or reverse flow flush. That will help get stuff out of the heater core.

 

I had the same problem upon purchasing my 99 over a decade ago. At 66k it had obviously seen some torture. The coolant system was full of rusty water. No 50/50 mix at all. After multiple flushes with no results I pulled the water pump. The impellers on the pump were half gone. It would only overheat while driving. Sitting in the driveway with the A/C on everything seemed normal. Being a career mechanic I’d never seen this before or even thought it was possible. This was a factory pump with steel impellers. Also, this may sound silly but make sure it it is bleed properly.

 

I never understood the point of doing this. It's August. Just go drive for a bit, let it idle for 5 minutes, and rev the engine. Does the fan spin much faster and make a roaring sound? If yes, your fan clutch is working properly. If no, it's shot. Granted this won't work in January, but it's not January.