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2000 4.0L Cooling System Issues

3K views 74 replies 15 participants last post by  mrblaine 
#1 ·
Hi everyone,

My 4.0 (new to me) had some ugly coolant, so I decided to change it. Never had overheating issues. Temperature needle would, at worst, touch the higher side of 210F (likely around 210, per my OBDII).

I drained the fluid and filled with distilled water several times before finally replacing the old thermostat (195F Motorad) with a Mopar 195F, filling with Zerex G-05, and installing a new radiator cap (18 psi).

In the process of burping the system, I left the radiator cap off until operating temp, and noticed my heater wouldn't work unless my radiator cap was on. The water pump heater hose was bone cold unless I had it on.
So, that was sorted to my knowledge.

Driving on the freeway was perfect. Once in high speed stop and go (drive half a mile at 45 mph, then hit a stoplight for 2 or 3 minutes), I noticed my temperature creeping up. I oberseved this several times. It would get to 220-230. This is after a while of stop and go with AC on. For the first 30 minutes, I'd see 205F pretty consistently.

One day, when completely cold, I opened the radiator cap and some pressure released and spilled fluid. I put the cap back on, and drove some short drives with no issues.

Another day, during extended stop and go, I got up to 220F again.

When I would hit these temperatures, I'd turn the AC off and it would be totally fine, dropping back to 205F in about 2 to 3 minutes.

Got my mechanic to look at it, he suggested I replace my radiator, so I did; it had some noticeable rust on the tubes and outside of the core. He suggested a 180F thermostat which I have in now. Has fresh coolant as well.

Now I understand using a low temperature thermostat has its problems, and I'm not a fan of this.
My question is, do you think my water pump could be causing these issues?

Fan clutch operates properly per some quick tests I did.
Mechanic doesnt susppect combustion leaks, and I have no symptoms. I also ran a successful compression test before buying the Jeep about 2 months ago.

Of course the Jeep runs colder on shorter drives, and colder than before, but it still seems to have an uncontrolled creep up in stop and go traffic.

2000 TJ, 4.0, 136k miles, 0331 cyl head
 
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#2 ·
You should have stayed with the 195F thermostat.

Did you burp the system after refilling? Some will chime in to say the system is self burping, but many others, including myself, have had air bubbles tried, until squeezing the rad hose a handful of times with the cap off.
If the system fluid was in poor shape initially, the water pump may need replacing.

How is the fan clutch?
 
#3 ·
I agree with the 195F thermostat.

The fan clutch appears to be working properly.

I guess my question is two-fold: how stable should I expect my temps to be at full operating temp, and is there any way to diagnose the water pump not flowing properly without removing it?
 
#6 ·
Do it again...pop your Heat in the cab on FULL blast ...not until you reach the normal operating temperature should you put that cap back on. Typically I let it get to operating temp, let the bubbles , bubble over into a bucket (you may need to add as it overflows). Then once you can feel upper rad hose hot AND the bubbles stop, put the NEW cap back on.

Are you using ONLY distilled water? 50/50 mix ? or Mixing straight Antifreeze with distilled? don't just use Distilled....
 
#7 ·
I used 1.25 gal of 100% coolant after my distilled water flushes then topped off with distilled (there was distilled water still in the cooling system). Really I'm hoping to hear people's opinions on poor water pump and fan clutch behavior. I'm having great results on non-traffic drives.
 
#9 ·
I had the EXACT same issues as you. To a tee. Hwy drives no problem , even at traffic ALL year I was fine. Until one day it was climbing temp sitting in traffic for 2-4minutes.

I replaced the rad cap (18lbs) and no more issues at all. Start with something cheap and simple ($6) and go from there.
 
#8 ·
First, the TJ's cooling system absolutely will self-burp itself of any trapped air by doing nothing but driving.

A good fan thermostat will be very stiff and hard to turn by hand when everything is good and hot.

Hard to diagnose a bad/weak water pump but if it hasn't been changed by now, a 2005 pump is likely on its last legs by now. Make sure to install a Mopar if you can find one. At the very least avoid store-brand water pumps from low-end auto parts stores like Autozone.

And I'd stop going to a mechanic clueless enough to have replaced the proper 195 degree thermostat with a 180 degree model in an attempt to stop it from running too hot. If he knew what he was doing he'd know that going with a lower temperature thermostat cannot force the cooling system to run cooler. If it could we could switch to 100 degree thermostats and only need a very small radiator.

A thermostat's only function is to set the engine's minimum operating temperature in cold conditions and to help it warm up faster. It will NOT cause or help an overheating engine to run cooler when the currently installed thermostat is functioning properly.
 
#11 ·
And I'd stop going to a mechanic clueless enough to have replaced the proper 195 degree thermostat with a 180 degree model in an attempt to stop it from running too hot. If he knew what he was doing he'd know that going with a lower temperature thermostat cannot force the cooling system to run cooler. If it could we could switch to 100 degree thermostats and only need a very small radiator.

A thermostat's only function is to set the engine's minimum operating temperature in cold conditions and to help it warm up faster. It will NOT cause or help an overheating engine to run cooler when the currently installed thermostat is functioning properly.
Thanks, it's great to hear some logic, not much of that outside of JF.

OK4WD insisted that a 160-degree thermostat would help, installed it without authorization. They also insisted that the factory cooling system can not be made to work with a well-maintained 4.0L. Insisted that an all-metal radiator and e-fan are necessities (why me ?!?).

Most small shops I've been to professed to be of the same opinion, so I wonder if this is more scam than misunderstanding?
 
#14 · (Edited)
I understand the thermostats operation pretty well now, I think. I definitely agree it will only lower the minimum temperature.

Before I change anything, I'd like to see if I can really suss out the problem. I've got plenty of time on my hands (I don't daily this rig), certainly more time than money to spend.

I drove around for an hour or so last night, logging coolant temp along the way to graph it. I observed, of course, a lower operating temp (read: too low) in the beginning. I made sure to hit some stop and go traffic. Temperature got to just under 210F in some instances. When I got moving, however, I noticed it would drop down to 185F again.

I think this is where some people get confused into using lower temp thermostats. I think it can "band-aid" an overheating problem, in the right circumstances. It's allowing the engine to dip lower than normal, sort of offsetting its inefficient cooling system.

I'm by no means happy with my current set up. One thing I was sure would test it was idling in the drive way at the end of the drive.

I did that, and my temp started climbing until 217F, when I shut it off. I may have had a poor cooling system prior to my initial flush, I just hadn't worked it hard until now, so I never observed a problem.

I checked my fan clutch once it was pretty cool (1 hour after) and it is super stiff. It acts the same at full cold. I can't spin it more than 1/8 of a turn, even forcefully. There is no up/down, in/out play either.

How hot should I expect the rig to get when idiling? Certainly it should level out. Does anyone think the fan clutch is bad?
 

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#15 ·
When your engine starts getting hotter, can you hear the fan getting louder? The clutch should kick in at some point and start getting faster, sounding more like a jet engine.

FYI, here's what the FSM says about testing the fan clutch:

VISCOUS FAN DRIVE

NOISE
NOTE: It is normal for fan noise to be louder (roaring)
when:
² The under hood temperature is above the
engagement point for the viscous drive coupling. This
may occur when ambient (outside air temperature) is
very high.
² Engine loads and temperatures are high such as
when towing a trailer.
² Cool silicone fluid within the fan drive unit is
being redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.

LEAKS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. If leakage appears
excessive, replace the fan drive unit.

TESTING
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when
spun by hand), replace the fan drive. This spin test
must be performed when the engine is cool.
For the following test, the cooling system must be
in good condition. It also will ensure against excessively
high coolant temperature.
WARNING: BE SURE THAT THERE IS ADEQUATE
FAN BLADE CLEARANCE BEFORE DRILLING.
(1) Drill a 3.18 mm (1/8 in.) diameter hole in the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). It should have a range of -18° - 105°C
(-4°- 220° F). Insert thermometer through the hole in
the shroud. Be sure that there is adequate clearance
from the fan blades.
(3) Connect a tachometer and an engine ignition
timing light (timing light is to be used as a strobe
light).
(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator (or air conditioner
condenser). Use tape at the top to secure the
plastic and be sure that the air flow is blocked.
(5) Be sure that the air conditioner (if equipped) is
turned off.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
(6) Start the engine and operate at 2400 rpm.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 88° C (190° F).
Fan drive engagement should have started to occur
at between 74° - 85° C (165° - 185° F). Engagement
is distinguishable by a definite increase in fan flow
noise (roaring). The timing light also will indicate an
increase in the speed of the fan.
(7) When the air temperature reaches 88° C (190°
F), remove the plastic sheet. Fan drive disengagement
should have started to occur at between 57° -
82° C (135° - 180° F). A definite decrease of fan flow
noise (roaring) should be noticed. If not, replace the
defective viscous fan drive unit.

CAUTION: Engines equipped with serpentine drive
belts have reverse rotating fans and viscous fan
drives. They are marked with the word REVERSE to
designate their usage. Installation of the wrong fan
or viscous fan drive can result in engine overheating.

CAUTION: If the viscous fan drive is replaced
because of mechanical damage, the cooling fan
blades should also be inspected. Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration. Replace fan
blade assembly if any of these conditions are
found. Also inspect water pump bearing and shaft
assembly for any related damage due to a viscous
fan drive malfunction.
 
#16 ·
When your engine starts getting hotter, can you hear the fan getting louder? The clutch should kick in at some point and start getting faster, sounding more like a jet engine.
When I let it idle at the end of the drive, it just maintained it's noise. It's not quiet.
When I raise the hood, there's definitely air flow.

I've heard of that test you mentioned. I may give that a shot. It seems tricky though.

I think I'll compare my fan sound to clips on Youtube and see where that gets me.
 
#21 ·
Alright,

Did another drive last night. Great low temps driving around town. Then I let it idle in the driveway. Popped the hood to check stuff out.
It stayed under the 210 needle the whole time. Until I closed the hood. Then it started to creep up a bit, getting to the right edge of the 210 line (I didn't have my data logging going, sorry for the imprecision). Keep in mind, yesterday, temps got to nearly 220. I hate to let it keeping going up. Maybe it would level out. I'm just worried about damaging something.

The fan was definitely sucking air into the radiator. It wasn't as loud as startup, though. Once I drove away (never shut it off), it roared really loud (I hit 2000 RPM shifting through 1st and 2nd), definitely louder than sitting in the drive. Temps dropped immediately. Dropped down away from the left edge of 210 mark.

Is it possible my fan clutch is engaging sporadically, or at too hot temperature?

My next thought is water pump could be bad.

I think I'm coming around to at least replacing the fan clutch to see what happens.
 
#23 · (Edited)
It's a two-row, aluminum core, plastic tank model from OSC, I believe.

It's not leaking. I do have a tiny spot of coolant just under the thermostat housing after driving. I bet the mechanic didn't seat the gasket/housing properly. I don't think it's causing my issues. No drip visible during idling or anything, just noticed after when it's back cold. No noticeable fluid level change in my overflow bottle.

Also, I checked the hoses, neither are bulged or collapsing. The upper is definitely hotter than the lower, upper is ~205F and the lower is ~185F, when my temps started to creep at idle.

I measured a few points on my radiator showing 140F-160F, so I don't think it's clogged.

Should the fan roar at idle too? It definitely does when I rev it up.
 
#34 ·
I replaced my thermostat with a Stant 195F and a new Stant 18psi cap. I think I'm happy.

With AC off I fluctuate between 203-208F.

With AC on its pretty pegged at 210F. When I hit a stop light I see 212/213F, but it comes down quickly to 210F once I get moving.

I'm in Houston with 95F ambient temp and probably 90% humidity.

I'll just keep watch of it if I plan to idle a while.
 
#37 ·
Because of the variable operating temps I wonder if there's something to Flowkooler's claim of using a higher flow rate to avoid hot pockets ?

I suppose HOAT jeepers (01 and up) would not have to worry about electrolysis after installing a Flowkooler ?
 
#38 ·
It isn't that simple. If they could demonstrate how a higher flow could interrupt the barrier wall insulation of the tubes and that somehow leads to better cooling, I'd like to see their work and how they arrived at it. Once shouldn't forget that the Jeep engineers have more resources at their disposal to design the system to work and I'll bet the flow rate is exactly where it needs to be to compensate for the thermal burden the system sees.

If they needed a higher flow rate, they are more than able to design a water pump to create it. Also don't forget that the dash gauge is little more than a glorified idiot light. The temps in the system are going to vary a fair bit as has been shown by those with live data loggers. The problem with that is none of us really knows what the max is supposed to be, what sustained is supposed to be and all we really need to know is whether or not it is in overheat mode or not. When it is, the gauge pegs and you have a problem. Until then, it's going to average the temps it gets to move the needle around a bit to sorta let you know it's working.

This is the same cooling system that gets put in the rigs they ship to the hot places in the world. They don't call up Flowkooler and install their pumps when they do it. If they did, there would be a severe duty cooling system option that the rest of the world would try to get their hands on.

Not to mention that the TJ cooling system is more than robust for what it is cooling. I've had more than a couple arrive to me with the radiators completely blocked with mud except for a spot directly in front of the fan blade about the size of a normal dinner plate and only when it got that small and the owner's started working them hard running up the mountain did it show signs of having a problem. That is more than 50% of the capacity fully blocked and only then was there an issue. That means the system is roughly 50% larger in cooling capacity than it needs to be. I restored them back to normal by removing the radiator and using the pressure washer with a high flow low pressure nozzle to flush the mud out.
 
#39 ·
Moving too much fluid through a heat exchanger too fast can cause just as much of an issue as not enough.
The amount of fluid that passes through in a given time period needs to match the thermal transfer properties of the heat exchanger.
Thermodynamics is not a simple subject.
If too much fluid passes too fast through a heat exchanges that is not designed for it the thermal transfer will be insufficient.
And, even that is WAY WAY WAY simplified...

Just think about it; if you wanted to drop the temp of a fluid by "x" degrees would you want to hold it in the heat exchanger while air passed over it, or move it through at high speed? And it gets more complicated when you're adding heat to the fluid at the same time like in an automotive cooling system. It's a very delicate balancing act.
 
#40 ·
That and at some point the higher velocity will lead to erosion and give the soft nature of aluminum and the relatively thin walls of the tubes, erosion is likely going to be an issue at some point.

This should help some. (not you) If you can read and understand a fair bit, it will help to understand why just tossing a "high performance" part into the equation as a solution without taking the rest of the system into consideration is probably not going to work.

https://www.hrs-heatexchangers.com/resource/comparison-laminar-turbulent-flow/
 
#44 ·
That's a fair point, I didn't know about the right side of the 0 before this thread. I used to think I needed to worry about anything over 210.
 
#47 ·
I have read this thread with interest as I just got a new (to me) 97 Wrangler. It originally was a 2.5 but someone put a 4.0L from a 98 Cherokee in it. Driving it home it overheated. Did some cooling stops but eventually rented a dolly and towed it the last 100 miles.
I found the cooling system totally contaminated with rust and sludge and the thermostat was, well, Non existant. No doubt the seller had issues that he did not represent.
I flushed the entire system several times until clear water came out of the radiator engine and heater core all individually
I filled it with water and flushing fluid and drove about 45 miles and all was well. Flushed the whole system again and ran at idle for about 10 minutes and it overheated again.
Frustrated I decided that I was going to change most of the components out and hopefully this should fix it. This thread really showed me how important individual components that are merely taken for granted and "burping process" can be. I think I have probably a combination of all.
I'm in the process of changing radiator, shroud, fan, thermostat, water pump and hoses. It was just that neglected that it's the right thing to do. Hopefully that will fix me up.
I have a question (and not wanting to steal this thread) I hope someone can chip in on. Due to the engine swap, the OEM shroud will not fit even if I move the fan from the right side of the engine to the water pump, the alignment does not match up (yes it was running without a shroud before with the fan only covering 70 of the radiator!!!).
Question is I'm going with a 2 core aluminium radiator and shroud with built in electric fan 1300 cfm. Do you see any major issues with this setup? Just don't think I have a choice.
Thanks.
 
#52 ·
Question is I'm going with a 2 core aluminium radiator and shroud with built in electric fan 1300 cfm. Do you see any major issues with this setup? Just don't think I have a choice.
Did you mean a 2 row? Radiators have one core.
I have yet to see an electric fan out perform the OEM belt driven fan/clutch setup...
 
#55 ·
From the Flowkooler website:
"Hold on...doesn't the coolant have to have more time in the radiator to cool?
No. But a lot of people still think so. We have come up with some explanations for the Doubting Thomas.
Debunking the I Can Have It Both Ways Theory:
The water has to have time to cool argument is most common one we hear. In a closed loop system if you keep the fluid in the heat exchanger you are simultaneously keeping it in the block longer. Unfortunately, the block is the part that is generating the heat. Sending hot coolant from your source (engine) through the heat exchanger (radiator) to the sink (air) will transfer heat as long as there is a temperature difference between the source and sink. The engine is still generating heat the whole time so why keep the coolant there any longer than you have to."

Pure marketing dribble!!!

Yes, flow that is too low is bad because the coolant stays in the block longer and absorbs more heat.

But, the coolant DOES need sufficient time in the radiator to shed heat through the fins to the surrounding air!

It's a delicate balancing act...

Unless someone took the time and spent the money to come up with a system that included a high flow water pump, fan, and radiator package that was carefully designed to work with the rest of the OEM cooling system it's all a bunch of BS.

And no one is going to do that!
Why not?
There is NO NEED!
The OEM cooling system was carefully engineered to do it's job properly. If kept in proper operating condition it does just that.
Would it be possible to design a system that operated more efficiently?
Sure it would. But it would take a large investment of time and R&D and the return would never come because the system design is perfectly sufficient as is.
And just a water pump alone is not going to do it...
 
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