94 XJ Running hot running out of things to check

[sberrett]

My 94 XJ with 250k is having some overheating issues that I cant narrow down and I'm about to throw in the towel and take it in to my mechanic.

Running around town the temp is fine and stays between 195-210f. Highway speeds is defintely hotter than i'd like to be at, and any kind of hill climb makes the temp gauge shoot up to the last mark below the red. At that point turning the heater on full blast will usually settle it back down to the 240f area. I live in Southern California so those of you that live here know the hwy climbs I'm talking about. I5 North going up Castaic, or I5 South Grapevine, but it's not just those, it's any kind of incline that starts making the temp skyrocket. This has been a problem for awhile. Add summer temps into the mix and it's just constantly running way too hot even on flat highways.

My setup
RE 3.5 lift, and 32's on stock gearing.
CSF Radiator (2670), Flowkooler, 195 tstat
New hoses (they arent collapsing)
New ZJ clutch fan from Napa
I've flushed the system and completely burped the system of air
I've tried 50/50 and 30/70 distilled water to concentrate mixtures
Efan is fine
And the mechanical fan shroud is intact.

The last thing I did this weekend was attempt to change the temp sending unit on the engine block out with a new one (Mopar) and now it seems to be reading at a higher temp than it used to. The dash gauge is now saying it's idling at 210, and will get up to 225ish at which point the efan will kick on. I've taken temp gun readings at the tstat housing and at the rear of the block where the sending unit is and it checks out to what the gauge is displaying. It sounds like the old sending unit was bad and this one is reading closer to what i'm really at.

At this point i'm wondering if I have a cracked head, or a bad head gasket, but i'm not seeing the obvious signs. My Jeep mechanic made the suggestion that it could be my gearing, but I don't really agree with that since it's ran hot even before I modded it years ago.

Any thoughts on what else I can do?

 

[JonnyCat63]

No one really knows why these piles overheat. I own 4 XJ's and I've run the gamut on this whole over heating issue. I think I've read every thread imaginable on the internet, and no one has a concrete answer, as in "this is why these XJ's overheat." Many theories, but nothing concrete.

And when I say I've changed everything, I mean everything. I've tried CSF, Champion, American Eagle, Spectra premium, Champion BC1193, custom built radiator from Bryce Thomas radiators, Cold Case radiators, Hesco water pumps, stock pumps, high flow T-stat housing, changing Cats and muffler, by passing the heater control valve, ZJ fan clutch, by passing the heater core, blah, blah, blah.

Here's what I've found. Take it with a grain of salt.

High flow water pump vs stock. No difference.
High flow T-stat vs stock. No difference.
CSF radiators. Sucked.
Champion Radiator. Just okay.
American Eagle radiator. Worked great, but Champion no longer makes that one. Also leaked after a few years.
Cold Case. Just okay. Didn't work as well as the American Eagle in my 97.
Custom Bryce Thomas radiator for my 95, not that good.
Champion BC1193. Works good in my 99.
Spectra premium. Works great in my son's 99. But this rig is bone stock. The 3 others have similar lifts, lockers, and builds.
ZJ fan clutch. Sucked, and was too close to any radiator except stock. I just use stock fan clutches always now.
Most of the other mods I did. Don't have any evidence they helped one way or another.

What I did is put a manual e-fan controller in the 3 trails rigs, and I just keep the temps down by using the e-fan sooner than it would turn on by itself.

My scientist brother in law thinks it is an air flow problem. It seems to work fine for me with the e-fan always running. I'm also in So-Cal, so in cooler desert weather off road, I don't have to use the e-fan as much. Hotter weather out in the desert, I can use the A/C as much as I'd like. On the freeway and in town, almost no issues with over heating. But they are mostly dedicated trails rigs, and only see pavement to and from off roading spots. Only my son's bone stock 99 is a daily driver. I'm thinking my BIL is right on the air flow situation.

I think there are 3 main problems with the cooling system.
1. The radiator is not tall enough. Even stock, it is probably at the max of it's cooling capacity. Not much you can do about that. If you look at all the Wranglers and such, they all have the same 4.0, but a much taller radiator. They don't seem to have nearly the cooling issues of XJ's.
2. There must be some passages in the block or head that are too narrow and susceptible to constriction from corrosion. Flushing and maintaining maybe will help.
3. I think the heater core is more problematic than people think. I think a clogged heater core contributes to over heating. I'm not sure, but a clogged heater core seems to maybe put a back pressure on the inlet side of the heater hose. I'm not sure about this, but some testing has made me think this is a possibility. When I by passed the heater core on my 99, I had better performance. Unfortunately, I changed to the BC1193 radiator at the same time. Also, a corroded heater core can send bits of debris into your radiator, causing it to clog up.

Here's what I would do.
1. I'd get rid of that CSF radiator and get a Spectra premium. Many have reported great success with the Spectra premium. Second choice would be a BC1193 from Champion Radiators. But they are pricey.
2. I'd thoroughly chemically flush out your cooling system. There's many threads on how to do this and what products to use.
3. If your XJ is old, and the cooling system has not been maintained well, then you heater core is probably hosed. I would bypass it, and change it if you need or want a heater. Do not try and flush it IMO. You can't properly clean it, and it's just going to spit out debris into your radiator. Change it or bypass it, but don't flush it and expect it to be as good as new. Everyone tries to flush it because it's a PITA to change. This has been my experience.
4. Add a manual e-fan switch.
5. Use a 50/50 mixture of coolant with distilled water only!. Don't let anyone tell you that a weaker 70/30 mix is fine. It is not fine and you will get premature corrosion. People have reported that water-less coolant works well, too. I don't have any experience with that.

Anyway, that is my experience and advice. YMMV. I just chose to put up with it and mitigate it with and manual e-fan controller. Hope that helps.

 

[Bent]

With the manual switch be careful to wire it so that the automatic on function works when the switch is turned to the off position.

 

[75SV1]

I wouldn't discount the airflow idea. I own a '75 Bricklin. Going to one of the National meets and other travels, I noticed that at 55 mph, the temps remained OK. Going above that, the temps would rise a bit. When I slowed back down, then it took the temps a while to go down. I talked to one of the Gurus on Bricklins. Didn't write it off, just who has the equipment to test that stuff. A few years latter he was selling an upgraded chin scoop. Also, another owner added a trans cooler.

 

[JonnyCat63]

Also, another owner added a trans cooler.

You're right. I forgot to include that I installed an auxiliary trans cooler on the trail rigs, too. I bypassed the radiator, too. No need for that here in SoCal.

 

[Unclewolverine]

Most mysterious xj overheating threads end up being solved by a new spectra radiator. They are cheapo units, but they really seem to work the best.