I'm looking for input and ideas here. I rock a 1991 Cherokee XJ. The body has about 238k miles, but we replaced the engine around 200k, followed by a number of smaller components as they also wore out, so it's newer than it looks. Most of the parts only have about 35k or less on them. New muffler and tailpipe coming soon. I'm gonna miss sounding like a Harley, but at least I'll be street legal... We live in the San Juans at about 6k feet elevation and this is my daily driver. I commute about 70 miles to work and back each day.

My issue is that when I sit in traffic, even briefly, or have to drive around town at less than about 35mph, the thermostat starts to rise significantly. It's kind of an overheating issue, though I never let it fully overheat. I just kick on the heat if I have to and try to drive at steady speeds above 35mph whenever I can to keep it happy. It responds well to both those tactics and the temp stays steady right where it should. It's fine on the highway, though climbing the mountain passes can have the the same "overheating" effect if I get stuck behind a slow moving tourist. Drive-thrus are a crapshoot. Usually if I can put it in park or the weather outside is chilly it will slow down the heating, but if I have to idle in gear it heats up faster. Of course, this happens mostly in the summer. I don't notice it when the weather is cooler (though I'm constantly running the heater or defroster in the winter, so...) Stop and go traffic gets stressful in the summertime.

Which is all to say that while 89% of the time everything is normal and running smoothly, it heats up when I idle in gear or go uphill, which seems normal, but it just heats up a little faster than I think it should. If I hit three red lights in a row, I'm edging toward the red line and I have to turn the heat on to cool down the engine and get the rest of the way home. That doesn't seem totally normal. Is this normal? Actual "jeeping" on the offroad passes is out of the question. I wouldn't be able to get more than about a mile creeping uphill in low gear before I'd need to stop and turn the engine off for awhile to prevent damage. That can't be right.

We've discussed putting some sort of secondary fan on it to keep it cooler, but I feel like an old Jeep Cherokee couldn't possibly have been designed so that it overheats every time I go up too much of a hill or idle in traffic at a stoplight. Sure, adding a fan might help cool it down, but I'm looking for the root problem. I'd rather fix that than slap a bandaid on it.

Has anyone else had issues with an older Cherokee threatening to overheat when it's idling, travelling up a steep hill, or when the weather outside is too hot? Is there some sort of vacuum line that could be blocked, do fans wear out over time (I always eyeball the fan when I check my belt and it seems just fine - turns easily, no nicks or damage visible), should I be checking my air filter more often, is my radiator somehow f****d? Should I be making some sort of offerings to the Jeep gremlins? Is it voodoo? Do these cars even have O2 sensors? Could it be something like that? I've torn this vehicle apart and put it back together a number of times and I'm at a loss as to what the issue could be. This is a new area of car repair for us. I just feel like there has to be something minor that we're overlooking here. We stay very up to date on fluids and routine maintenance. This has always been an issue since we bought this vehicle in 2015, but it wasn't a daily driver until we moved last year and I'm tired of stressing about it. I just want my Jeep to be happy.

Very early on, when we first bought it, we had to replace a leaking radiator cap. Could there be some sort of long term damage from that issue? I've had to replace the HCV about once a year, but the one in there now seems to be holding up just fine.

I'm open to any and all suggestions of what I should be looking at, replacing, adding, etc. I just want to not have to worry about it now that I live in a town with traffic and stoplights and increasingly hot summer commutes. Alternatively, has anyone added a secondary aftermarket fan, and if so, was that a viable option? How did it work out? Thanks in advance for ideas, pointers, or conspiracy theories - anything that gets us there.

 

If it generally only runs hot while sitting or driving slow, the Fan Clutch is the most likely culprit...

 

Will check it out this weekend. I have all sorts of work scheduled/planned to get done before it snows...

 

First things first, eliminate the HCV. Completely unnecessary. Jeep eliminated it themselves in later years. Hoses for 97+ to the heater core.

Second, the cooling system will degrade over time and doesn't like being neglected. I suggest doing a complete overhaul of the cooling system, and do a complete flush before tearing the old components out. Make sure you replace everything, make sure your shroud is in good shape, get a new e fan, and don't use tap water or additives.

Once you have replaced everything, flush and fill once a year, keep it serviced, and it should last a while.

 

Yeah, I know that HCV is a pain and totally unnecessary. They're super chintzy too. They break if you look at them the wrong way. We just haven't gotten around to bypassing it yet and it's like $8 and five minutes to just throw a new one in there when it starts to leak. I think a radiator flush at the very least is definitely in order. It hasn't been done since we bought it, as we were spending a lot of time with it off the road doing repairs and getting everything up to a good level of maintenance, and the previous owners were not work-on-the-car type people. I kind of figured it could be something along those lines ("the cooling system will degrade over time and doesn't like being neglected.") Sounds like I'm adding some more big work to my before-it-snows list. Thanks for the tips.

 

the scenario you give about HCVs is not normal.

They generally burst apart and you lose all your coolant in a hurry.
Or, they blow apart when you accidentally bump them and give you a 210* coolant bath. I speak from experience on that one. Ticking time bombs.

 

^^^
x1 !!