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XJ Cooling System Deficiencies & Solutions

The 3 row radiator fit SMOOTHLY WITHOUT any trimming! Since I had to disconnect the transmission cooler, I decided to add a auxiliary transmission cooler in front of the radiator (& behind the grill).

Everything has run great for months... recently I was traveling at 60 MPH up a steep hill, outdoor temp was 60ºF, & had the defroster on (means that the A/C was on), and it again spiked to 265ºF.

I turned off the defroster & turned on the heater to bring the temperature back down. It worked quickly...

This is what I have done so far to the cooling system:

High flow Mr. Gasket thermostat (stock temp)
High flow thermostat housing
Hi-Flow water pump
3 row aluminum radiator
New radiator cap
New upper & lower hoses
(3) electric fans with adjustable thermostat relay (set at 190ºF)
Added a hood air scoop (facing in reverse to create a negative pressure area in the engine compartment to increase air flow)
4 complete system flushes
New Heater Hoses
50/50 coolant

The electric fans are wired into the automatic relay, so that they are forced to come on with the A/C.

I have about 1000 lbs of gear on/in my 1999 XJ 4.0L A/T 4x4 (safari rack, after market bumpers, winch, rock sliders, a dead boar in cargo area, mother-in-law on roof, etc). The drivetrain is stock, OEM tires/wheels, w/a 3" lift. Lowered transfer case with SYE & new driveshaft.

Can anyone come up with a reason why this thing is still overheating??
 
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if any of you are up for some real reading and excellent tech read the tech article on pirate4x4 pertaining to cooling systems. there is a lot of miss information floating around that leads to a lot of wasted money on issues that don't exist.
 
The initial post in this thread is bullshit. It has been proven over and over again that an XJ cooling system in good working order works just fine, even with lifts and bigger tires. However, the original stock single core radiator eventually needs to be replaced with a larger double or triple core radiator.

It is true that XJ cooling systems are prone to problems. The cause, from the mouth of a factory Jeep engineer, is from the shape of the radiator. The styling of the XJ requires a long radiator but with a short height, which limits it's overall capacity to cool. The XJ radiator has fewer tubes but the tubes are longer, which is inefficient. A radiator with more, but shorter, tubes will cool better. Once the water travels so far down the tube, it won't really get any cooler, so the extra length is wasted and the radiator is inefficient.

For this reason, the XJ cooling system doesn't have a lot of reserve cooling capacity, so if there is any part that begins to have a problem there can be overheating. If the cooling system is in good condition, it will cool just fine. Many of us have strokers, which put out more power and more heat, and with a good higher capacity replacement radiator along with all other parts being stock there are no heating problems. I race mine, with a stroker, and the only part of my system that isn't stock is the radiator, which is a multi-core replacement radiator, and it's never overheated while pre-running or racing.......and that's pushing soft comp compound 40" tires with low air pressure, so it's quite a load on the motor.

While a bad thermostat, bad clutch fan, or bad aux fan will cause overheating, the majority of overheating in XJ's is caused by a partially plugged radiator. I've also seen, and experienced, a new radiator become partially plugged after a year or two because the engine didn't get backflushed when the new radiator was installed, and crud from the engine partially plugs the newer radiator.
 
I have a completely new exhaust system connected to the stock manifold. It is the stock diameter, new CAT & muffler to the tail pipe... It is less than 4 months old & there is no damage to it.

So that can't be it.
Is it something other than the cooling system then? Perhaps the engine is not running correctly and causing an overheat?
BTW, good article and since many XJs do experience overheating, an important article. My '98 still runs a bit hot in the summertime at highway speeds and if/when offroad rock crawling. Setup is Auto, 4.0, 33x12.5 ATs, 4.56 gearing, 5"(+-) lift. I guess I'm just too used to my Chevy work van running at 195 degrees regardless of external conditions. My mechanic points out that for starters an XJ is significantly larger and heavier than a Wrangler so that alone puts added stress on the cooling system.
dn
 
I run my 4.0 XJ with most of the A/C system and the condenser removed and I have the mechanical fan removed as well. I took the auxiliary electric fan and hard wired it to an on/off fulltime ignition switch in the cab. I have a new radiator, coolant, hoses and t-stat and I have not had anywhere close to a problem...yet. Granted I do live in northern Washington state where we are lucky if we see maybe a couple days a year in the 90's. I run 33" tires, stock gears, 7" lift, and have an auto trans.
 
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This thread is so full of fail.

You'll find a trend in all of these XJ forums all over the world. Someone has cooling problems. They upgrade to a gimmick radiator and still have cooling problems. Then comes the high flow water pump, followed by bigger fan clutch or electric fans, upgraded thermostat .. and they still have cooling problems.

Eventually they flush the block and or fix their blown head gasket and it runs cool.

Every damn time.
 
are you running the shroud kits for the fans as well?

Yes, you have to run the fan shroud. The radiator is very short and the fan diameter is larger than the radiator, so the fan sticks down below the radiator. The shroud is needed for the best performance.
 
Everything has run great for months... recently I was traveling at 60 MPH up a steep hill, outdoor temp was 60ºF, & had the defroster on (means that the A/C was on), and it again spiked to 265ºF.

I turned off the defroster & turned on the heater to bring the temperature back down. It worked quickly...

This is what I have done so far to the cooling system:

High flow Mr. Gasket thermostat (stock temp)
High flow thermostat housing
Hi-Flow water pump
3 row aluminum radiator
New radiator cap
New upper & lower hoses
(3) electric fans with adjustable thermostat relay (set at 190ºF)
Added a hood air scoop (facing in reverse to create a negative pressure area in the engine compartment to increase air flow)
4 complete system flushes
New Heater Hoses
50/50 coolant

The electric fans are wired into the automatic relay, so that they are forced to come on with the A/C.

I have about 1000 lbs of gear on/in my 1999 XJ 4.0L A/T 4x4 (safari rack, after market bumpers, winch, rock sliders, a dead boar in cargo area, mother-in-law on roof, etc). The drivetrain is stock, OEM tires/wheels, w/a 3" lift. Lowered transfer case with SYE & new driveshaft.

Can anyone come up with a reason why this thing is still overheating??


Backflush the motor and recheck the radiator. Put the mechanical fan back on, you know, the one you said was no good in your original post, and with a fresh stock clutch fan, the one you said was also no good in your original post. And, make sure you don't have a bad head gasket. A shop can do a chemical test.

You claimed to know so much originally, but now you can't figure it out. Amazing, and typical. This XJ cooling stuff is so simple, and yet people complicate the crap out of it.
 
can anyone give me a quick description of how to back flush the motor? I did a cheapo parts store coolant flush before replaceing the radiator, but i still have overheating issues when climbing long hills at freeway speeds any time the outside temp is over 70 degrees.

94, 4.0, automatic and AC. 32x10.5 tires on stock gears. Radiator is a 2 core. tstat is 180, water pump is OEM replacement.
 
One thing I noticed in the OP as well is that he says removing the clutch fan will help the water pump pulley - FALSE, the mech fan is on its own pulley, not the water pump. Altho, an electric water pump is a good idea depending on cost.
 
I'm not sure what is meant by backflushing either, but I had an overheating problem last summer. Changed out waterpump, t-stat, fan clutch, rad. cap...nothing worked. Then I burped the radiator and problem solved: Remove radiator cap (assuming open cooling system), turn on engine, watch for bubbles. For the first 30 to 45 minutes I just got a steady stream of tiny bubbles and then I got a sudden 3 inch drop in my fluid level...problem fixed, no more overheating. Call it vapor lock, gas bubble, trapped air, or whatever...the fix is easy and dirt cheap. Not sure its so easy with a closed system however. It might help to point the vehicle uphill to facilitate movement of trapped air toward the radiator.
 
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I'm not sure what backflushing is either, but I had an overheating problem last summer. Changed out waterpump, t-stat, fan clutch, rad. cap...nothing worked. Then I burped the radiator and problem solved: Remove radiator cap (assuming open cooling system), turn on engine, watch for bubbles. For the first 30 to 45 minutes I just got a steady stream of tiny bubbles and then I got a sudden 3 inch drop in my fluid level...problem fixed, no more overheating. Call it vapor lock, gas bubble, trapped air, or whatever...the fix is easy and dirt cheap. Not sure its so easy with a closed system however.


Another way to help get air out of the system is pull the sending unit for your temp gauge, which is at the rear of the head on the drivers side.. remove it and let any air escape.
 
I have found that in an auto XJ, the transmission fluid transfers alot of heat back into the coolant when running up a steep hill. This can actually make the engine overheat because it counteracts the cooling being done by the radiator. It helps a great deal to use an auxilary (like a B&M) tranny cooler and don't run the tranny fluid through the radiator.
 
I'm not sure what is meant by backflushing either, but I had an overheating problem last summer. Changed out waterpump, t-stat, fan clutch, rad. cap...nothing worked. Then I burped the radiator and problem solved: Remove radiator cap (assuming open cooling system), turn on engine, watch for bubbles. For the first 30 to 45 minutes I just got a steady stream of tiny bubbles and then I got a sudden 3 inch drop in my fluid level...problem fixed, no more overheating. Call it vapor lock, gas bubble, trapped air, or whatever...the fix is easy and dirt cheap. Not sure its so easy with a closed system however. It might help to point the vehicle uphill to facilitate movement of trapped air toward the radiator.



Yeah, anytime coolent is let out, like changing a radiator or water pump, it's possible to get air trapped in the block and it will always overheat. Parking uphill helps, and running it a little then re-burping it.

Backflushing is sticking a garden hose in the radiator hose and running water through the system backwards from it's normal flow. You can get a flush kit, or chemicals, put the stuff in and let the engine idle for awhile and then backflush the system. Should always be done when a radiator is replaced.



I have found that in an auto XJ, the transmission fluid transfers alot of heat back into the coolant when running up a steep hill. This can actually make the engine overheat because it counteracts the cooling being done by the radiator. It helps a great deal to use an auxilary (like a B&M) tranny cooler and don't run the tranny fluid through the radiator.

Good comment, I wonder how much difference it makes. I know a lot of us who have lifts and bigger tires also have bigger tranny coolers, and many bypass the radiator. I know I bypass the radiator.
 
Goatman - You don't need to be a condenscending d!¢kh#@d. We'd all be better if you shared your vast years of wasted time, experience, and worthless knowledge, instead of passing judgement on us clueless idiots who needlessly pad the pockets of the aftermarket auto parts manufacturers. Words to remember - a sniper doesn't give away his presence until he fires!

The OEM cooling system still sucks, regardless of the problems that I'm individually having. You say that the OEM cooling system is great... then blab on about how the radiator is the wrong shape, airflow insufficient, blah, blah, blah... Which side of your face are you going to talk out of next?

I did "back flush" the cooling system. I installed a garden hose flushing T in the heater hose & ran & drained the system 2 times, on 2 occasions (2 x 2 = 4). An application of Prestone Cooling System Flush each time (or maybe you didn't bother to read the entire thread).

I didn't do the radiator "burp." Makes sense, as even babies burp after a good meal! I did observe that the fluid level inside of the fluid reservoir was going down... that could explain it! I'll try that I report back if I get any air belching out. Next is the head gaskets - I know a torn gasket is SO readily visible on a casual inspection (how could I have missed seeing it?).
 
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