For a few weeks now I've been having some overheating issues. I'm a newb to cooling stuff, so hoping I could get some insight from you fine folks to fix my 98 XJ 4.0. I'll be doing the work myself as much as possible.

During normal driving, temp stays around 210-220 no problem. However after driving for awhile, and when idling or just crawling along sitting in traffic, temp will creep up very slowly, and then all of a sudden jump up to 250-260 or maxed out on the gauge and the "Check Gauges" light comes on. As soon as I can start driving at speed again, the radiator can do it's thing and temps drop back down to normal. This only happens after driving for some time, when the engine is good and hot, and so far only on these hot summer days. Any clue why it spikes all of a sudden like that? One time it suddenly dropped back down to normal too, still while idling in traffic, very strange.

I got the Jeep last year, and haven't touched anything with the cooling yet. Just from my research so far, I was thinking a good flush is in order, maybe new thermostat, water-pump, hoses, maybe even radiator? I'm thinking of replacing the AC condenser as well while I'm at it, since it seems to have a leak.

What parts will I need exactly to overhaul the cooling system, and any recommendations on manufacturer? O'reilly's generic parts good enough? I do plan on wheeling it eventually, and it will be slow rock crawling on hot days, so need it to stay nice and cool. Thanks!

 

Water pump
New hoses (could be crimping themselves shut)
New thermostat
New fan clutch (Napa makes a good one)
Make sure fan shroud is there and complete
Is the electric fan coming on at temperature?
Flush it out really good. Like several several times.

 

^^^ Typing while you were posting!

If your going to replace the complete cooling system you can flush the block and heater core after you've removed the parts. My auxiliary fan and fan shroud and thermostat housing were good. Here's a list of what I replaced.
Radiator (Spectra from Auto Zone)
Fan clutch (NAPA #272310)
Water pump (Gates)
Radiator cap (Stant 16ps)
Hoses (all)
Thermostat (MOPAR 195)
Water pump inlet tube ( I used a brass 5/8" hose barb x 3/8" NPT fitting instead)
50/50 coolant

Since I had everything removed I also replaced the serpentine belt and idler pulley. Both Dayco.

If your XJ is an auto trans and your going to be crawling and/or towing you may want to consider an auxiliary cooler. ( I've got a B&M #70264)

 

Thanks for the info!

It already has a tranny cooler, I believe its a stock unit. It does look pretty beat up however, may be worthwhile to replace it while I've got it all apart.

For the radiator replacement, would one from Auto Zone or O'Reilly be good enough with future plans on wheeling, versus some aftermarket aluminum 3 row whatever?

 

The factory radiator is all you need. I also have the Spectra radiator, and it provides plenty of cooling. I can go off-road with the AC on in 90* temps and not go above 210-220*.

 

Sweet, thanks! I'll update this thread down the line if I run into issues.

 

try putting the heater on full bore...if the temp drops to normal, that is indicative of a poorly functioning radiator

 

Since the Jeep seems to cool decently at speed, but not when sitting I'd be looking at the fans. Does the electric fan work? If it works then I'd be looking at getting a replacement/upgrade (the 4 cylinder Cherokee fan clutch or the zj standard fan clutch are both an upgrade). I personally have run spectra radiators and didn't realize until recently that they are only 1" core vs the 1.25" core that other companies offer. So if you're buying a new one might as well get as much cooling out of it that you can. Rock auto has the core thickness of all the radiators listed in the specs. While on the topic of rock auto they are much cheaper to get the parts from than any box store I've seen. If you have the money and ability I'd go ahead and do the radiator, water pump, thermostat, radiator cap, fan clutch and the belt wouldn't be a bad idea since you'll have it off. I haven't looked at it all recently, but should be able to stay under $200 for all that from rock auto.

 

Don't forget to use this:
https://www.cherokeeforum.com/f10/ro...7/#post3568561

 

Speaking of Rock Auto, they seem to have the best prices on Gates hoses for XJ over anybody. I don't think their most expensive 195 thermostat is over $5 either.

 

So I let it idle in a parking lot today when it was pretty hot out, and waited for the temp to spike. Once it did, I opened the hood and sure enough the fan stopped spinning right as it spiked.

It takes awhile for the fan to stop working, I had it idling for about 20 minutes before it stopped. Other than that it will turn on and run, however it does look like it spins a little slow.

Does this sound like a bad fan clutch? I will eventually replace and flush everything when I have some free time, wondering if I can just replace the fan clutch for now to stop the overheating.

 

Yep. Bad fan clutch.

Did your electric fan come on?

 

Whoops - Actually, the electric fan is the one that turned off, and seemed to be pretty weak. The main engine fan was working fine, the electric fan was the one that shut off after a while. I guess the fan clutch is not the problem. I did say I'm a noob to all this cooling stuff!

Now that that's cleared up - What would cause the electric fan to suddenly stop? Just a bad fan, or thermostat or something else? And can the e-fan stopping be enough to spike the temp all the way up, even with the main fan running?

 

The e-fan will shut off when it's told to by the PCM. If it's being told to shut off, it could be the temp sensor. There are two on some years - one for the gauge, and one to actually do stuff! (Stupid, I know!). So, your temp gauge could be telling the truth, and the actual working sensor could be lying, OR, your actual sensor is accurate, and the temp gauge is lying to you.

It's also possible that the fan is on its way out and can't keep working once its own temperature gets too high, so it quits, then of course your engine temp spikes.

If you want to diagnose that possibility, here's what you could do:

1. Disconnect the fan.
2. Get your multi-meter connected in place of the fan, so you can see when the fan should turn on, and when it should turn off.
3. Get the car hot.
4. watch the voltage AND your temperature (so you don't trash your engine!).
5. When the engine gets warm enough, you should see 12v at the fan connection. You should NOT see it turn off when the temp goes high.
6. Naturally, shut the engine off before it gets too hot.

Better yet, you could do this with the fan connected if you get some insulation-piercing probes. This would be a better test, as you'll KNOW when the fan shuts off, and you can see what the voltage is doing.

Those readings will tell you if the fan is the problem. If not, it's upstream. The relay, the temp sensor, or even the PCM.

Another quick test you can do is to swap the fan relay with another relay in the PDC. There are several that are identical. Then see if the problem persists. If it goes away, it's the relay.

All that said, I'm betting on the temp sensor, but testing beats parts-swapping any day.

 

Thanks for all the tips, I will try and narrow it down to one of those components before replacing stuff!

I'll post back if I figure out the issue, thanks again