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Discussion Starter · #1 ·
Hey there. I have a 2001 Dakota sport with the 4.7 V8. It's been a great truck for me but a couple of weeks ago it started saying it was overheating with the "check gauges" light coming on and the temp gauge rapidly moving up. The day before I had hauled a couple pails of sand for my wife and then changed oil on it. After the oil change I washed the motor as it was fairly dirty, it had been a couple of years. The next day my wife drove the truck to church, a 10 min drive and on the way back,, the Check gauges light came on. She was only a block from home so she parked at a gas station and walked home. After lunch I went and drove the truck home. It was getting hot again according to the gauge. So far I have checked all fluids, all fine, no leaks anywhere. No milky oil or oily anti freeze. I've changed the thermostat and it still got hot. I just changed the temp sensor and it still shows it's overheating. Upper rad hose and lower get hot and warm respectively. Coolant flows through upper hose when cap is off so water pump should be ok. I'm at a loss, for the tuck to go from not even running warm to showing it's overheating after only an oil change and wash has me confused. Electrical fan comes on when it gets warm, mechanical fan is kinda stiff when cold and loosens up when warm. Any ideas? Sorry for long story, just trying to get all the info in the story to help with diagnosis.
 

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mechanical fan is kinda stiff when cold and loosens up when warm. Any ideas?
I think I remember this cooling system problem/post.
Anyway, it should be the other way around with your fan: it should spin freely when cold, but then as it warms up, that's when, due to the thermal spring, the clutch should engage the fan & it should get stiffer.
That kind of sounds like maybe a bad fan clutch.
When it is running hot, is the pulley driven fan spinning?

There is a kit you can get to pressurize your radiator when the engine is off & see if the system is holding pressure. I have never used one, but I've read about it, frequently, on this site. You could do a search on that.
I know you have indicated that the coolant level is not going down, but considering all else you have checked (but I wouldn't rule out the fan clutch yet) I'd probably be wanting to be sure the system was staying pressurized to (I think) 20 psi.
 

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Here is one of those kits from Horrid Fright:


Looks like it should be straight forward to use.
$91, but who knows, you might some day have an occasion to use it on something else.
I'm not sure, but maybe Advance, or the like, has loaners.
If a head gasket was leaking super hot combustion chamber gases into one of the coolant jackets, those hot gases going into the cooling system would probably put you into an overheat condition, regardless of the condition of everything else.

But your OP about that fan/clutch interests me.
 

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Oh, hey,sorry, but last night I was thinking about two things at once & I got them inter-tangled.
Where I still do think that a coolant system pressure test would be a great resource to have available for troubleshooting coolant systems, the test that I was thinking that would be applicable was: checking your coolant for exhaust gas (which would indicate whether super hot gases from a combustion chamber was over heating your coolant).


"The last scenario is a compression leak into the water jacket. This is the last check, after all the other scenarios have been eliminated. This test is looking for exhaust gas (CO2) in the radiator, indicating a blown head gasket. "


And as far as your fan clutch goes, I remember a couple of people posting about actually REMOVING their pulley driven fan assembly to gain a couple of more HP and reporting that their electric fan did the job just fine. I cannot attest to that, personally, & I am NOT removing my pulley driven fan, but if what they say is accurate, I guess that would mean that even if your fan clutch was bad, you shouldn't be severely overheating (because your electric fan is theoretically sufficient).
 

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Discussion Starter · #5 ·
Thanks for all your input Matt. I think you may be onto something with the belt driven fan. It has resistance to turning by hand when cold and spins like an old solid mount fan when cold. As it warms up it seems to start slipping to the point where I could stop it with my hand with the motor running. As you mentioned though, the electric fan seems to work fine and turns on when it gets warm. My cousin has the kit/tool to find exhaust gas in the rad so I'll borrow that and our local Canadian tire store has the pump kit to pressure the system up and check for leaks. Thanks again for the input.
 

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That definitely does not sound right about the belt driven fan, to me, but,
the reason I am somewhat skeptical of the belt driven fan clutch being totally responsible for a severe overheat is because, as typed previously, there have been (at least a couple of) people who have posted about completely removing that fan so they could gain a few more HP & gas mileage, & they have basically said that their electric fan did the job for them.

(Personally, I like the idea of having a fan that I KNOW is turning when the engine is turning and the electric fan being a supplemental backup.)

I'll wish the best for you on this, meaning that I am hoping for you that you do NOT detect exhaust gases in your coolant, because that would mean that you have a problem that has now turned out to be not-simple.

But anyway, the clutch isn't super hard to change, there is some junk that needs to come out of the way first (at least on my '03 w/ 5.9 there is).

You didn't say what the mileage was, but If it's got "a few" on it, & the exhaust gas check turns out negative for gases in your coolant & the pressure check shows it holding pressure, I think I'd seriously consider changing BOTH the pump AND the clutch. (Theoretically the clutch & H2O pump have the same lifespan. Theoretically.) Parts wise, from Rock, it's really not a high priced job.


Anyway, good luck on this, and when you finish your checks & stuff, feel free to let us know what you found out.
 

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Rock Auto (who admittedly is in the business of selling parts) offers this:
"Service Tip: Always replace belts and tensioners together. Old tensioners will reduce a belt's lifespan, and can lead to issues such as overheating, a dead battery, diminished power steering, or poor air conditioning performance."

I change the belt on all my vehicles every five years, and I admit to not changing my tensioners at the same interval. I am going to go out on a limb & say that most people probably don't change their tensioners whenever they change their belt, so it might be you have the original tensioner installed.
 

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The alternator, water pump/fan, A/C, power steering pump etc all turn when the motor is running.
Sorry, I missed this reply because of the way it was embedded into the quote of Ralph's reply.

Anyway, at this point you know you have an overheat condition that does not seem to be the caused by all the usual/simple suspects. (I.E. thermostat, rad cap, coolant level. . . .)

That makes me want to think kind of outside the box. Although not the "classic water pump failure", could the water pump's impeller be moving water but be severely corroded to the point where it isn't moving enough water? Could the tensioner be worn out & although keeping the S-belt taut enough to turn the H2O pump pulley at idle (when you can observe it), but when the engine is operating under any kind of driving load, could it be letting the belt slip?

Once the easy obvious stuff is eliminated, you are kind of left to scratch your head & think of what straws you can grasp at. Personally, right now, I would be really interested in the results of the test for exhaust gases in the rad.

I know that you are questioning the correlation between washing the motor & your present issue, but I am inclined to think that this is just a coincidence. Shit happens & things break down; I could be wrong, but I am thinking that this just happened to happen after the motor wash.

I don't know how many miles you have on your Dakota, or what kind of schedule you have maintained performing preventive maintenance on the cooling system (flushes & such), but I suppose another possibility is that the internal water passages have been slowly obstructing over time & finally became completely occluded (not unlike the coronary arteries of a heart attack patient). That is just another possibility that I would throw out for consideration.
 

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Discussion Starter · #16 ·
Sorry, I missed this reply because of the way it was embedded into the quote of Ralph's reply.

Anyway, at this point you know you have an overheat condition that does not seem to be the caused by all the usual/simple suspects. (I.E. thermostat, rad cap, coolant level. . . .)

That makes me want to think kind of outside the box. Although not the "classic water pump failure", could the water pump's impeller be moving water but be severely corroded to the point where it isn't moving enough water? Could the tensioner be worn out & although keeping the S-belt taut enough to turn the H2O pump pulley at idle (when you can observe it), but when the engine is operating under any kind of driving load, could it be letting the belt slip?

Once the easy obvious stuff is eliminated, you are kind of left to scratch your head & think of what straws you can grasp at. Personally, right now, I would be really interested in the results of the test for exhaust gases in the rad.

I know that you are questioning the correlation between washing the motor & your present issue, but I am inclined to think that this is just a coincidence. Shit happens & things break down; I could be wrong, but I am thinking that this just happened to happen after the motor wash.

I don't know how many miles you have on your Dakota, or what kind of schedule you have maintained performing preventive maintenance on the cooling system (flushes & such), but I suppose another possibility is that the internal water passages have been slowly obstructing over time & finally became completely occluded (not unlike the coronary arteries of a heart attack patient). That is just another possibility that I would throw out for consideration.
Thanks for all the ideas. I'm going to borrow a tester to see if there are exhaust gases in the coolant system and hopefully a cooling system pressure tester. Our local tool rental place no longer carries one so I'll ask my folks in my car club if anyone has one. I understand about the belt possibly slipping while under load but I haven't driven it since this first happened. It overheats while idling in my driveway. I also understand about the system slowly plugging up over time, but wouldn't the motor slowly start to run hotter as time goes on, rather then be operating at normal temps one day and then the next day start overheating? There is also the possibility that it's not actually overheating and just the gauge is not working properly as there is no boiling over or sounds of boiling like any other vehicle I've ever had overheat, no steam, no filling the overflow etc. Next step is the exhaust gas test.
 

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I suppose it is a theoretical possibility that your gauge is malfunctioning.

I recently acquired a FSM for my '03 Dakota & I just now did some interesting reading related to the operation of that gauge. (I would think that it would pertain to an '01 as well.) I won't quote the whole thing verbatim, as as slowly & poorly as I type that would take me all night, but I'll paraphrase the highlights that I think are applicable.

[. . .] this gauge is controlled by the instrument cluster PCB based upon cluster programming & electronic messages received by the cluster from the PCM over the PCI data bus.[ . . .] The instrument cluster circuitry controls the gauge needle position and provides the following features:

Eng temp message - each time the cluster receives a message from the PCM indicating coolant temp is between the low end of normal (130f) & the high end of normal (264f) the gauge is moved to the actual relative temp position on the gauge scale.


I will skip the section on eng temp low message and go straight to:

Eng temp high message - Each time the cluster receives a message from the PCM indicating coolant temp is above 252f the gauge needle is moved into the red zone of the gauge scale & the check gauges indicator is illuminated in a 6 gauge cluster or the eng temp indicator is illuminated in a 4 gauge cluster & a single chime tone is sounded [. . .] remains illuminated until the cluster receives a message that eng temp is below 252f until ign sw is turned to OFF, which ever comes first.

(I had once been led to interpret this as meaning that when your temp is between 130f & 252f range, the needle on the gauge is going to go to just one preset spot, regardless of what your actual temp is, as long as it is in that range. If that was actually correct, this would also mean to me that if your system was all gunked up & not circulating properly, the system that Dodge used or still uses(?) to indicate coolant temp at your cluster would not track a trend of gradually elevating coolant temperature; it would just indicate that you were in one of 3 ranges--temp under 130f range, temp between 130f & 252f range, or temp in the oh ****, that's way too hot range. However, upon reading this for myself just now, I am not positive that that is how it should be interpreted.)

Communication error - if cluster fails to receive an eng temp message, it will hold the needle at the last indication for about 40 seconds or until ign sw is turned to OFF, whichever comes first. After 40 seconds, the cluster will move the gauge needle to the low end of the gauge scale.

Actuator test - each time the cluster is put through the actuator test, the eng coolant temp gauge needle will be swept to several calibration points on the gauge scale in a prescribed sequence in order to confirm the functionality of the gauge & the cluster control circuitry.

I'll skip the preambles & go straight to the test. I will note, however, that the FSM does type a warning in bold print to disable the airbags before attempting any steering wheel/column, airbag, seatbelt tensioner OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE.

Let your conscience be your guide, & don't say that I did not repeat the warning.

1)begin test with ignition switch in OFF position.
2)depress odometer/trip switch button
3)while holding odometer/trip switch button depressed, turn ign sw to ON pos, but do not start engine.
4)Keep the odometer/trip switch button depressed for about 10 seconds, until CHEC appears in the odometer display, then release the odometer/trip switch button.
5)a series of 3 digit numeric failure messages may appear in the odometer display, depending upon the failure mode. If a failure message appears, refer to Instrument Cluster Failure Message chart for description & proper correction.


(You will have to get back to me on that & I will go to the chart.)

If no failure message appears the actuator test will proceed as described in Step 6.

I don't think 6 is applicable,but . . .

6) The cluster will begin the Vacuum Fluorescent Display (VFD) walking segment test. This test requires operator to visually inspect each VFD segment as it is displays for a pass or fail condition. First, all segments will be illuminated at once. Then, eache individual segment of the VFD will be illuminated in sequence. If any segment fails to illuminate, repeat to confirm. If failure is confirmed: replace cluster.

7) is the bulb check, and I don't think that this is applicable to you right now.

8) The instrument cluster will perform a gauge actuator test. The cluster circuitry positions each of the gauge needles at 3 different calibration points, then returns the gauge needles to their relaxed positions. If an individual gauge does not respond properly, or does not respond at all during the gauge actuator test, the cluster should be removed. However, check that the gauge terminal pins are properly inserted through the spring clip terminal pin receptacles on the cluster PCB before considering cluster replacement. If the gauge terminal connections are OK, replace faulty cluster.
9) Actuator test is now complete. Cluster will automatically exit self-diagnosis mode & return to normal operation.at completion of test, if the ign sw is turned to OFF during the test, or if a vehicle speed message indicating that the vehicle is moving is received from the PCM or the PCI data bus during the test.
10) Repeat test if required.


* * * *

WHEWW!!
(I actually didn't paraphrase very much.)
And to think that I was going to suggest buying a cheap direct temp gauge from Amazon or Harbor Fright or Advance or someplace like that & temporarily replacing the MoPar coolant temp sensor with the one that came with the cheapo gauge & just using that,temporarily, to confirm whether you were, in fact, overheating.

Anyhow, if you have any questions because it seems like I left something important out, let me know & I'll read through it again & try to fill in any blanks that I missed.
 

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Discussion Starter · #18 ·
Thanks Matt for the info. I'll check into it if it warms up in the next couple of days. It's dark when I leave for work and dark when I get home so it's been relegated to weekends to look at.
 
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