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  #1  
Old September 24th, 2009, 16:54
BarFlyFisherman BarFlyFisherman is offline
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XJ Cooling System Deficiencies & Solutions

I wanted to share my thoughts about the stock cooling system, and the reasons for making various modifications.

Please, not debate the benefits of Aluminum VS Copper. That horse has already been beaten to death, buried, dug up, and the skeleton beaten some more. Go read the archived thread about that debate.

Stock cooling system limitations/ parameters/ assumptions:

1. The XJ was not designed for creeping along at low speeds in high temperatures.

2. The primary engine cooling fan is RPM dependent: low speeds = low rpm/slow fan & low CFM = HIGH TEMPS & OVERHEATING!

3. Driving slow also means that the velocity of the incoming air is slow: low speeds = low CFM = HIGH TEMPS & OVERHEATING!

4. The output of the OEM water pump is RPM dependent: low speeds & low rpm's = low flow = HIGH TEMPS & OVERHEATING!

Other influencing factors:

1. There might be an optional A/C condensing coil in front of the radiator core. This coil "pre-heats" the air passing through the core, reducing it's effectiveness.

2. Adding an after market transmission cooler or power steering cooler in front of the radiator, further restricts the airflow through the core. These also "pre-heat" the incoming air, reducing the effectiveness of the radiator core.

Issues:

1. We need to move more water (gpm's) at lower rpm's.

2. We need to move more air (cfm's) at lower speeds & rpm's.

3. Using the A/C causes the condensing coil to add SUPER-HEATED air directly in front the radiator core.

4. OEM fans do not move a sufficient volume of air at low speeds. These were designed for stop & go city driving. At idle in trafffic, you don't have much load on the XJ. But climb hills, full of gear, with the A/C on, at >5 mph & you have an overloaded system!

Solutions:

1. Move more water at low RPM's:

a) Electric water pump - this is why these are so popular. They are not to save HP (pure fiction), but to ensure a stable GPM output across the broad RPM range.

b) Any of the high-flow aftermarket water pumps. Look for one that has a pump curve that will increase the flow at lower RPM's (where you need it), and levels out at the higher RPM's when you don't (higher RPM's usually means you're going faster).

2. Move more air at lower MPH/RPM's:

a) Increase the capacity of the stock fans. Install a higher CFM electric fan &/or a more efficient clutch fan.

b) Remove the OEM fans all together. Remove the radiator shroud, engine fan clutch & fan, and remove the stock electric fan (You're also removing the load on the water pump shaft & bearings!) AND REPLACE THEM with an aftermarket electric fan system.

I used (3) 9" Dynamics 1100 CFM fans that all kick on together. I used the old A/C trigger, to override the new fan relay, regardless of the temperature. I drilled & tapped the flat spot on a new high flow aluminum thermostat housing with a 1/4" pipe tap. Then I installed a 1/4" MPT X 3/8" FPT brass adapter (hardware store) to adapt the new threaded water temp sensor to the housing for the fans. I like this better that the probe set up, as it is the most accurate.

3. Cooler Air to the Radiator Core:

a) We must face reality... we just do not have that much room to work with. To that end, we simply cannot eliminate the added coolers in front of the radiator. Personally, I used the integral transmission cooler within the radiator, to cool the power steering fluid instead of adding one more thing in front of the radiator. I've got a Hayden 1405 (aka: 405) cooler on front for the automatic transmission fluid ($35 EBay).

b) With those limitations accepted, we must provide a means to dissipate the additional heat, as the incoming air, just is not as cool as we need it to be. Increasing the CFM of the puller fans, does help - A LOT! Higher wind velocity (unlike water higher velocity) cools things off much faster (convection)!

c) Another solution is to provide a larger radiator. With the removal of all of the factory fans, there is now the room to install a thicker core (3 CORE vs the OEM 2 CORE). And there is more room to work in there without scrapping up the knuckles!

Benefits of a 3 core radiator:

1. Metal end tanks - enough said. Whatever you do, get rid of the crimped on OEM plastic tanks. Even is you're staying with a 2 core radiator. The crimps do come loose from vibration & wear. Plastic & metal just don't bond together!

2. 33% more water jacket volume. NOTICE: I did not say cooling capacity... here's why:

a) The first 2 rows pre-heat the incoming air before it reaches the new 3rd row. So claims of 33% extra cooling is misleading. It is probably more like 28-30%.

b) Any added after market coils & the factory optional A/C coil pre-heat the incoming air, so that there just isn't the ability to effectively dissipate heat by the time the air gets to the 3rd row. Adding these coolers in front of the core lowers the additional cooling capacity to about 22-25%.

c) Still 25% an additional cooling capacity is nothing to laugh off. That, along with the 3300 CFM's from (3) fans, will bring the added cooling capacity right back up to 33%+!

3) Personally, I chose a 3 Core, 100% aluminum radiator (radiatorbarn.com $175). I do come from a family of rocket scientists... they insist on aluminum cores, primarily for the weight savings over the copper equivalent. They are ever so slightly more efficient that copper. The key when selecting a radiator is the density of the fins. The more fins per cubic inch, the greater the surface area in which to dissipate heat. But too dense does restrict the air flow....

Thermostats:

I've played around with many different configurations of temperature settings. I've tried high-flow models & lower temperature settings (180F). Things acted all haywire.... the check engine light came on with both styles of thermostats - here's what I surmise:

a) The high-flow thermostat does not create any back pressure in the system. The water just flows through the engine block too fast for the efficient transfer of heat to occur.

b) The lower temperature thermostat prevented the engine from getting up to the correct operating temp (210F!). The 210F was selected, as this operating temperature results in the cleanest emissions. Because this optimal temperature is programmed into the computer (ECM), the engine freaks out when it sees anything less for a substantial period of time (normally the stock temp would close to help raise the temp).

I went back to the stock temperature thermostat, but selected a HIGH quality calibrated thermostat (Mr Gasket/Stant). Everything's working great since.

I only installed a new high flow thermostat housing, so that I had a pristine surface when it came time to install the new gasket. I also wanted the larger sweet spot to drill & tap, that the aftermarket casting provided.



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  #2  
Old September 24th, 2009, 17:36
ipkyss ipkyss is offline
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Re: XJ Cooling System Deficiencies & Solutions

A completely stock good working system is all you really need. If there are no issues at all. You will not have problems. I have been out wheeling in 95-100 degree weather with the ac on, with only one stock electric fan. No clutch fan. I took it off over a year ago to upgrade to dual electric fans and never got around to it.

I am not saying dont upgrade your jeep. Just saying to make sure everything else is right first. It doesnt help to upgrade and only cover up another problem.
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  #3  
Old September 25th, 2009, 17:08
BarFlyFisherman BarFlyFisherman is offline
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Re: XJ Cooling System Deficiencies & Solutions

I kindly disagree with the assessment that the stock cooling system is adequate. Every XJ forum on the net from Rhode Island to Australia, has multiple major threads about the inadequate cooling systems.

I read of way too many failures of the individual components, fan clutches, blown plastic tanks, cracked heads & blocks, and seized engines to not reach the conclusion that the cooling system is marginal at best (in reality IT SUCKS!).

As enthusiasts we tend to push our rigs beyond getting groceries & a trip to the ski resort. We should be called "extremists!"

My 1999 4.0 would PERIODICALLY OVERHEAT... LIKE AN INSTANTANEOUS SPIKE TO 260-270F! Usually when I was driving slow (5-10 MPH) in 4X4, climbing hills with the A/C on. The outdoor temp could be 65F or 100F - it did not matter.

The fan clutch was okay, water pump wasn't leaking, & hoses were hard (the pump was a pumping!). The cooling system is serviced regularly.

So, I started with a cooling system flush, replaced the coolant & thermostat (generic 195F). It ran fine for a few weeks, then did the temperature spiking thing again - this time while driving 70 on the interstate at 9 pm, 90F weather, up a 5% grade with A/C on. Driving solo, no trailer, no kids, heavy gear...

So, I decided to bite the bullet & replace the radiator & water pump. With those cheapo plastic tanks on the ends, it's not worth having a radiator shop boil & rod it.

Since I was doing the water pump, I decided that I might as well get rid of that NOISY fan clutch & fan. Can't sneak up on anything with that thing screaming your arrival! Besides, EVERYONE has problems with those damn things anyway (that's why there are so many fan clutch eliminators in use!).

Since I made the upgrades to the cooling system, the problem has not reoccurred (maybe my shotgun approach worked). Better to be "wrenching than wenching" anyway!

Now, I'm a ninja coming down the street. I might find out who's been parking on the lawn, sitting in my spot on the front porch couch, and putting the toilet seat down!

But, I beg the question, that maybe yours is the freak (for being trouble free)!!??
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  #4  
Old September 25th, 2009, 17:32
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wolfpackjeeper wolfpackjeeper is offline
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Re: XJ Cooling System Deficiencies & Solutions

Most of the bitching I have seen on the forums eventually can end up being attributed to a fault in the cooling system. Every time I have had a problem with temps it has ended up being a failed component. When everything is up to specs it runs fine. Including when covered with mud and running slow during a hot carolina summer.

My stroker is running a 3row rad in front of it. But with the rest of the system stock. Oh yea, and currently have no fan. I took the mechanical off to avoid killing a radiator on a jump or deep water crossing, and the electric gave up the ghost. I have had a few taurus fans to install just no time. I ran it around all day today (it needed the excercise) and give it a run once a week just to keep it running well. It does fine in the florida stop and go driving as well.

adequate is exactly the word I would use to describe the XJ cooling system. It works well with no qualms for 95% of the trucks out there, if kept in good working order. I watch people jump to conclusions and upgrade everything on here, just to find out it still does not work correctly, till they find what was actually wrong.

I will give you that most people could benefit from picking up a 3 core radiator, but honestly, there is nothing really wrong with the rest of the system.
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  #5  
Old September 25th, 2009, 18:39
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Blaine B. Blaine B. is offline
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Re: XJ Cooling System Deficiencies & Solutions

The XJ clutch fan does not use the water pump as the mounting point. For ZJ's they do, yes, but not XJ's.
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  #6  
Old September 25th, 2009, 18:45
RTFM RTFM is offline
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Re: XJ Cooling System Deficiencies & Solutions

Agreed, the stock system - at least at stock specification is fine.
Typically the replace everything method is just trying to "make up for" a deficiency not yet found.

The hundreds of thousands of XJ's doing the LA, Houston, Phoenix, Ft. Lauderdale, Atlanta ...(et all)... 2MPH freeway crawl (sometimes for hours on end (been there done that in Dallas too many times)) in the 110 degree tarmac would be overheating by the thousands daily if the stock configuration was not at least adequate.

My thought is that by replacing the water pump to a high flow unit - thinking the factory spec pump is going bad, appears to do the trick. But what if the real issue is a blocked passage internally?
So by having a higher fluid flow in all other passages now is "crutching" (My word) the blocked passage, taking up it's "work" - it did not fix the issue and return the cooling system back to original specification but found a work around that the system accepts.

I agree that the parts available now as aftermarket parts are sub-standard quality compared to factory original "off the line in 1995 (etc)" and I too hav moved to a 2 core radiator (not wanting a plastic tank radiator that was my only other choice at the time to get me running) and have added a Mac's aluminum overflow bottle in my '89 simply I cracked 3 plastic bottles in a years time.

I don't attribute it to a poorly designed cooling system, I call it cheap chinese parts.

P.S. Welcome to
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  #7  
Old September 26th, 2009, 16:34
BarFlyFisherman BarFlyFisherman is offline
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Re: XJ Cooling System Deficiencies & Solutions

Thanks.... been lurking for years.

Without doing an engine tear-down there is no way to locate a blocked passageway. However, a blocked passageway would result in the occurrence being rather regular & not so intermittent. An intermittent failure, is indicative of a component that selectively fails when under extreme stress.

This is where I am going with this thread... the military Jeeps are nothing like their civilian counterparts. Why, because the military wants them designed for extreme stress conditions. The individual components are over designed & collectively the system becomes bulletproof.

We take an XJ "soccer mom's grocery getter" and turn it into an extreme off-road rock crawling pumpkin buster. This is why almost everyone experiences cooling system issues. The XJ was not designed by Chrysler for this kind of abuse!

If a component fails, why replace it with an OEM piece of garbage, when for a few dollars more you can get a much better part? But, you cannot replace parts individually, as the upgraded components will place stress on the remaining OEM components.

If the net system is operating on ruggedly build & over-designed parts, then the individual parts have to work that much less. They are not taxed to the point of failure. Rather, the collective additional "over-kill" reduces the stress on the overall system & individual parts.

I stand by my statement...

The stock cooling system sucks!
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  #8  
Old September 26th, 2009, 17:04
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wolfpackjeeper wolfpackjeeper is offline
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Re: XJ Cooling System Deficiencies & Solutions

I will continue to maintain that your statement is incorrect.

Perhaps you could preface it and say that YOUR stock cooling system sucks. But as for the entire line of production vehicles, nope

Last edited by wolfpackjeeper; September 26th, 2009 at 17:08.
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  #9  
Old September 26th, 2009, 19:31
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jdxj jdxj is offline
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Re: XJ Cooling System Deficiencies & Solutions

Pish Posh

The stock system may or may not be good enough for a stock jeep, But a built jeep with big tires ect is just too much for it to handle. My 01 was fine for the first 3 years till I lifted it and but on some bigger sneekers now it sucks for sure. I have kept it well maitained but it gets hot every single time I go wheelin and overheats at least once in every 3 trips. I've been going to order up that ff dynamics system for a while now but just can't seem to scrape up the cash. Every thing I read about it says that it works great and everyone that has it can't speak highly enough of it.


Bottom line the stock system may or may not be good enough but if yours is giving you problems then it's time for an upgrade.

What model radiator did you use? Also did you have to do any cutting or fab work to make it fit?
TIA
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  #10  
Old September 26th, 2009, 19:47
AL BUNDY AL BUNDY is offline
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Re: XJ Cooling System Deficiencies & Solutions

I have had 5 XJ's and about 70 other vehicles, mostly old 4x4's and muscle cars. XJ's do seem to have more cooling problems most of the other vehicles I have had. Just the fact that there are so many threads about overheating kinda says the stock cooling system isn't that great.

X2 on the fact that any truck you lift, add big tires, etc will need an improved cooling system.
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  #11  
Old September 26th, 2009, 19:53
JeepAddict85 JeepAddict85 is offline
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Re: XJ Cooling System Deficiencies & Solutions

stock system being adequate or not...this is all very good information to have. thanks for putting it all in one thread! i have replaced my radiator with another stock one (stupid drain valve broke off inside and wouldnt stop leaking). soon im looking to go the dual electric fan route...hopefully that will help out while crawling.
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  #12  
Old September 26th, 2009, 21:38
JRW7072009 JRW7072009 is offline
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Re: XJ Cooling System Deficiencies & Solutions

I would have to agree that with a stock XJ the cooling system may be fine, but for a lifted XJ its not enough or just doesn't quite do the job. The way I think about it is take a YJ or a TJ and lift them with big tires and you rarely see them over heat and take an XJ and do the same and more then likely its going to have cooling issues. A guy from work has a 2000 TJ with a 9/D44 and 40" iroks and his cooling system and motor are stock and he never has issues.
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  #13  
Old September 27th, 2009, 08:30
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Pharaoh XJ Pharaoh XJ is offline
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Re: XJ Cooling System Deficiencies & Solutions

Yes the stock cooling sucks & this is the with all XJ wheelers here Egypt.
Cairo is hot & the traffic is crazy, I have a 94 XJ auto 155k+ the cooling is great as long as I am cruising 40+ mph at any temp, as soon as I stop in traffic, the temperature starts to rise, yesterday I got 118mph so the engine seams still strong.

The real issues start when I hit the sand, the thick sand seems to upset it alot even when going a 40mph with good headwind during winter.

I changed the radiator with a 3 core
+ new water pump
+ new fan clutch( even bolted the fan to the pulley)
+ hood spacer mod, fan override mod

-------------------------------------------

& it overheats

I have 2 tricks left:

1= cut out the hood right above the fan shroud (cowl type)
2= I think there might be an issue with the heater plumbing I always have one the hoses extremely hot, my guess is that the heater is bypassing the radiator and blowing hot water back into the engine/pump ????
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Old September 27th, 2009, 09:25
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JNickel101 JNickel101 is offline
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Re: XJ Cooling System Deficiencies & Solutions

Pretty sure if you're not running the heater, it isn't circulating fluid thru the heater core. Do you ever even use your heater in Egypt? I'd consider bypassing the whole heater setup if you don't....

If you have an auto tranny, anytime you make the tranny work harder (i.e., in sand), you're gonna heat that fluid up and that will affect your radiator performance - unless you bypass the radiator and have a separate tranny cooler.

I'm really considering going with the FFDynamics fan setup, with the shrouds. But first is some big ass hood vents from Race Ace
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  #15  
Old September 27th, 2009, 11:14
fasteddieyj fasteddieyj is offline
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Re: XJ Cooling System Deficiencies & Solutions

Quote:
Originally Posted by Pharaoh XJ View Post
Yes the stock cooling sucks & this is the with all XJ wheelers here Egypt.
Cairo is hot & the traffic is crazy, I have a 94 XJ auto 155k+ the cooling is great as long as I am cruising 40+ mph at any temp, as soon as I stop in traffic, the temperature starts to rise, yesterday I got 118mph so the engine seams still strong.

The real issues start when I hit the sand, the thick sand seems to upset it alot even when going a 40mph with good headwind during winter.

I changed the radiator with a 3 core
+ new water pump
+ new fan clutch( even bolted the fan to the pulley)
+ hood spacer mod, fan override mod

-------------------------------------------

& it overheats

I have 2 tricks left:

1= cut out the hood right above the fan shroud (cowl type)
2= I think there might be an issue with the heater plumbing I always have one the hoses extremely hot, my guess is that the heater is bypassing the radiator and blowing hot water back into the engine/pump ????
118mph in an XJ? Your a braver man than I am.
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