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XJ Cooling System Deficiencies & Solutions

I'm baaaaack...

I'm still overheating... to recap:

Extra weight/gear: I have about 1000 lbs of gear on/in my 1999 XJ 4.0L A/T 4x4 (safari rack, aftermarket bumpers, winch, rock sliders, rear swing tire carrier, 2 gerry cans). The drivetrain is stock, OEM tires/wheel size, w/a 3" lift. Lowered transfer case with SYE & new driveshaft.

I've replaced the following (with NEW parts):
flushed out the system 5-6 times now... clean as can be & no debris/rust (I've even placed an old pantyhose on the flush line to see what debris I could capture - nada)
radiator (3 row), metal tanks, 30% thicker than 2 core
2 ROW:
OLfPRwFTr6CIuYFUbF6UtA
http://picasaweb.google.com/lh/photo...eat=directlink
3 ROW:
http://picasaweb.google.com/lh/photo...eat=directlink
radiator cap
(3) 10" 1300 cfm electric fans (all three come on together, A/C forces activation regardless of engine temp)
water pump (flowkooler)
upper radiator hose
lower radiator hose (with factory hose & inner wire spring)
thermostat
thermostat housing
serpentine belt
hood air scoop (in reverse to create negative pressure area under hood)
using 40 coolant /60 water
power steering & A/C coolers still in OEM locations.
completely new exhaust - (except manifold: new pipes, cat, & muffler)
New head gasket (mag'd the head, no cracks, everything looked great, heat was flat, no signs of bridging, tears, breeches to the outside, or cross contamination)
Added an aux transmission cooler (in front of, but not onto radiator)
Dexron VI transmission fluid
Royal purple oil
burped it & burped it
even had a shop install the coolant mix with a pump & recovery system to ensure that there was no trapped air

Finally WENT BACK TO THE OEM FAN & CLUTCH (NEW - $$ OUCH!), electric aux fan and stock fan shroud...

Now, I've been through the aftermarket circle, and back to the OEM set up.

Still getting temperature spikes, I'll run around 210ºF then will suddenly spike to 265º, but only when the A/C is on.:flame:

Is there something that could cause the A/C to go to a crazy high temperature & thereby affecting the radiator temperature (not allowing the radiator to sufficiently cool the engine coolant)?


ANY ROCKET SCIENTISTS (or retired Jeep engineers) OUT THERE SITTING QUIETLY IN THE WINGS???
 
Barfly,

Are you using the stock temperature gauge? Does it only happen when driving or can it replicate itself while parked? My F-150 used to pull this same routine when the A/C was on but what I found was a faulty electrical connection and no real temp spike. I found a mechanical temp gauge and hooked it up and found nothing out of the ordinary even when the other gauge would be way off the red.

Good luck with the Jeep.

Side note; read through this entire thread this morning. Good info, my 90's leaking some anti-freeze (and every other fluid) but the temps have maintained so far. Hoping to get the bugger in to the garage in a few days and start fixing some leaks.
 
Last edited:
I bet it's wiring...

temp generally doesn't "spike" very quickly, since the block/coolant have a pretty decent amount of thermal mass. How fast is it rising from 210 to 265?
 
It slowly creeps up to 215º from around 200º. When the A/C is turned on it begins to climb, sometimes it hammers to 265º within 60 seconds.

I can replicate it idling & while driving. It is definitely overheating, as the coolant is boiling out of the reservoir, gurgling & making hissing noises.

It is not the temperature sensor, as I've verified it's reading with an infrared thermometer (heat sensor gun).

Does anyone ever heard of a bad idler pully or A/C compressor, slowing down the serpentine belt, and therefore slowing down the water pump & flow through the block and radiator?
 
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If it were a pulley, I would suspect a 100% overheating issue. Not an intermittent one like you are saying... I was having an overheating issue with my 89 with a 4.0 auto tranny and N242 Transfer. I spent close to $5000 in parts and leighbor at three shops to find the problem to be a pin hole leak in a heater hose. I didn't have the tools at the time to do a cooling system pressure test, but after one shop told me it was a cracked block, I broke down and bought a cooling system tester a long with a compression tester. when I pressurize the system, coolant came shooting out of my hole.. I couldn't find it because it was directly under my surge tank, and with the cap blowing off made it really hard to see.

My point in all this is... go back to the basics... recheck all your hoses, hose clamps, make sure you aren't leaking from the t-stat housing or water pump. get a cooling system tester and make sure that the system isn't leaking some where it shouldn't be. Also when doing the pressure test, get some die to make sure you don't have a cracked block. run a compression test as well. as stated earlier, you could be having problems with your ignition system (like the coil not getting enough voltage when the A/C is running). These are just some ideas, you can take them for what they are worth... I am no XJ genius, just a mechanic that has been around a time or two (usually in the diesel world)

On the the 2 core or 3 core radiator debate..... 3 cores offer better cooling overall compared to a single or even 2 row radiator, why else do they use them in HD car applications, and as a bare minimum for the old diesels?
 
I took out the NEW radiator to have it pressure checked, and discovered that the rim on the radiator cap was bent ever so slightly. After having a new neck installed, all of the issues that I was having went away...

Until yesterday...
I was out working at the ranch yesterday. I had made it into one of the back canyons in the early morning. I began raining about 10 am. After repairing fences all day, I forgot about the fact that the rain would make the road really muddy. It was 42ºF, windy & raining. Not what I'd describe as overheating weather.

I had the defroster on (which activated the A/C) to defog the windows, was in 4x4 low, A/T in 1st gear. By the time I had driven up the steep road in ultra-low (3 miles), the temp climbed to 230ºF. Not quite the red-line that I had been experiencing, but un-nerving none the less.

Anyone experience slight increases in temp under these type of conditions??
 
jeeperjohn said:
Seriously, there is an issue with the A/C. It could be that it is low and getting very hot. Bad compressor might cause that.
Click to expand...

Not how it works, bro... inefficient compressors and/or low charge would actually add less heat to the radiator/cooling system.

An overcharged system as well as a blocked condenser or bad aux fan could cause a rise in heat, but these conditions would also
create a rise in system pressure and I'm pretty sure our rigs have a high as well as the low pressure cut-out switch built in.
 
newbie here and im having overheatin issues, im wondering what seems to be the best trail tested high flow water pumps and also where do i get a high flow thermo housing. and would a plain old dual electric fan setup help everything
 
ya its been flushed a couple times. is there a way to test my stock electric fan i have never seen it come on. also what is an open cooling system? how does it work?
 
Ok. I'm glad I read through that thread. It really sounded like the OP new what he was talking about on page 1... so I read on... Only to find out you put all oem back on and still have issues. So for goodness sakes take the dang jeep to a real mechanic and figure out whats wrong with it. A qualified mechanic would have saved you hundreds of dollars by now not to mention you will have a warped head soon.
 
BarFlyFisherman said:
Go back and read this LONG thread from the beginning. There is a lot of GREAT information throughout it. It addresses the whole system and a lot of the bad information posted. It's too late to start all over again...
Click to expand...

Fixed that for you. :)



Every time I see this thread come up, I die a little inside.
 
Well, be prepared to die a little more...

I took the new radiator into the radiator shop. They pressure tested it & discovered that it would not hold pressure Turns out that the seat & mating surfaces for the radiator cap were not flat or perfectly round. They soldered on a new neck & it held pressure.

The XJ has ran fine without overheating since this repair back in October, 2010. It did see minor spikes when under load (towing a trailer uphill).

In December, 2010 I put the triple electric fans back on (removing the OEM electric fan, shroud, clutch & whirly bird). I have taken it on a couple of long trips, towing the trailer for added weight & stress. The minor spiking has disappeared (does this prove that a larger AT cooler, larger radiator & higher CFM fans keeps it cooler?).

Still no overheating, spiking, or fluxuations in temperature. As the weather warms up, and I have a chance to tow the trailer uphill in 100ºF+ heat, we'll see if this additional cooling capacity does the trick.

Personal opinion: The factory cooling system is still marginal when the XJ is under heavy load, A/C on, high ambient air temperatures.
 
So you got it running w/o overheating and then modified it. Why didn't you just leave it alone. You say stock is marginal but it sure seemed to finally run w/o overheating once you took it to someone who knows what there doing. I bet you have a reverse rotation pump in there and don't even know it.
 
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