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Discussion Starter · #1 ·
So I had to travel to Charleston (SC) today for a funeral. That's about 180 miles one way. I left this morning and made it with no issues; the truck ran well. I attended the funeral and drove as part of the procession to the cemetery (about 10 miles); again, no problem.

However, on my way back home during the first 40 miles or so of my drive, my truck started doing something it has never done before. I was driving about 50-55 mph and the O/D OFF light comes on followed by the TRANS TEMP light and the truck behaves as though I've turned off the O/D with the switch on the gear shift (downshift and RPMs increase). I tried pressing the O/D button, but it did not respond. The first time this happened, the cruise control was on and engaged but it did it again later when the cruise was off. I hit the brake and tapped the accelerator and the lights went off. A few minutes later it did it again.

After the second episode, I pulled over and checked the trans fluid thinking it was probably low. Nope; full. I got back on the road and drove another 16 miles or so and it did it several more times. It seems that if I give it gas immediately after it happens, the lights go off and it goes back into O/D. This occurred on the stretch of US 17 between Charleston and I-95.

Here's the other weird part. I stopped to fill up just before getting onto I-95. Once I got onto the interstate, I started out slow, 55-60 not sure if the weirdness was going to continue, then worked my way up to 70. For the next 120 miles or so (the rest of my drive home), no problems. It disappeared as quickly as it appeared. I don't know what caused it to happen; I don't know how to replicate it.

Any ideas? :confused:

I'm thinking about changing my trans filter and fluid; that was my first thought when this happened. I had it flushed back in January after I bought it. I'm also considering adding an aftermarket trans fluid cooler.

Any assistance is appreciated.
 

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I was driving about 50-55 mph and the O/D OFF light comes on followed by the TRANS TEMP light and the truck behaves as though I've turned off the O/D with the switch on the gear shift (downshift and RPMs increase). I tried pressing the O/D button, but it did not respond. The first time this happened, the cruise control was on and engaged but it did it again later when the cruise was off. I hit the brake and tapped the accelerator and the lights went off. A few minutes later it did it again.

Any assistance is appreciated.
The transmission temp light is turned on by the PCM or CTM (central timer module).
If it's turned on by the CTM as an indicator, the CTM gets it signal from the PCM, that gets it's signal from a transmission temperature sensor (thermistor) in the valve body of the transmission.

The way it works is that the PCM will determine when the transmission
can go into O/D by temperature data it gets from the transmission sensor.

The transmission fluid cannot be too cold or too hot in order for the O/D to engage or stay engaged.

So there is a temperature range from the Transmission temp sensor that the PCM expects in normal operation.
If that temp range (5volt sensor) is exceeded, then the PCM
decides to disengage the O/d unit, which drops the gear ratio from 4->3 and the engine rpm/fan increase
will help to move air flow through the rad-transmission cooler on the rad, to cool the transmission fluid enough
so the temp sensor feedback can inform the PCM, it's ok to re-engage the O/D unit again.

Why, I don't know, but maybe it's something to do the design of the Chrysler O/D unit.
The PCM controls the engagement/disengagement of the O/D with the 3->4 shift solenoid and the TCC (Torque Convertor Clutch) solenoid.

The O/D indicator is controlled by the PCM. When you push on the O/D OFF BUTTON on the turn signal stalk. all you are doing is sending the PCM a signal that you are requesting the PCM to disengage the O/D until you press it again. I think it works as a flip-flop.

The PCM has a data link bus and communicates with the Instrument cluster controller and the Central Timer Module.


I think in your case, the transmission was probably overheating because the thermistor temp sensor is a very simple reliable device.
 

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Discussion Starter · #3 ·
So perhaps the easiest way to ensure this doesn't happen again is to upgrade to an external transmission cooler.

I just can't figure out the timing of this problem. Why would my tranny be overheating at the beginning of my return trip (when it was cooler) and no issues after 3 hours on the trip up and the last 2 hours of my return.

Additionally, I'm not sure if outside temp factors into this, but it was probably 80 at the the hottest point of my trip yesterday. I did a couple of hours on the road a few weeks ago to test out my newly repaired A/C and it was close to 100 outside. No transmission problems.

I'll be going to DC around Christmas, which is about a 10 hour drive one way, and I want to take my truck so I need to make sure this issue is fixed.

Thanks!
 

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So perhaps the easiest way to ensure this doesn't happen again is to upgrade to an external transmission cooler.
Probably, yes.

[/quote]
Additionally, I'm not sure if outside temp factors into this, but it was probably 80 at the the hottest point of my trip yesterday. I did a couple of hours on the road a few weeks ago to test out my newly repaired A/C and it was close to 100 outside. No transmission problems.

I'll be going to DC around Christmas, which is about a 10 hour drive one way, and I want to take my truck so I need to make sure this issue is fixed.

Thanks![/QUOTE]

Well besides putting on an aftermarker transmission cooler, you may need to check the condition of the rad, since the engine can certainly run hotter than what the temperature range of the temp sensing sensor is supposed to be sending back.

If the tranny fluid is not being cooled sufficiently by the rad and it's normal transmission cooler tank attached
to the rad, the temperature can build up enough that the PCM disengages O/D and sets the trans temp indicator.

The PCM prevents engagement of the O/D convertor clutch and overdrive clutch when the fluid temp is below 10 degrees C (50F).

IF the fluid temp reaches 126C (260F), the PCM causes a 4->3 downshift and engages the convertor clutch.
The overdrive lamp in the instrument panel illuminates when the downshift to 3rd occurs.

The PCM will NOT allow 4th gear operation until the fluid cools down to 110C (230F).

So you may or may not have some kind of blockage in the transmission cooler lines? Perhaps a reverse flush may
clear out the blockage, if that is the case.

In any case; here are a couple things you need to investigate:

1. Condition of the rad..is it providing adequate cooling (judging by the engine operating temperature guage)
while on the highway. Obviously if it went up to 260F (thats well above boiling point of water at 212F).
2. fluid flow to transmission cooler tank on rad, perhaps a minor blockage is preventing proper transmission fluid
cooling? Maybe a reverse flush of the tranny too?
 

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Discussion Starter · #5 · (Edited)
It sounds like I may be in the market for a new radiator (or having mine serviced if possible). On really hot days my truck runs just over 210 (OEM gauge which I realize is not terribly accurate) with a 160 thermostat. For the record it never even hit 210 yesterday.

However, now that it seems it could be a factor in this issue, I should probably take a closer look at the radiator.

I'm looking for a trans cooler now.

Thanks for the help!
 

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It sounds like I may be in the market for a new radiator (or having mine serviced if possible). On really hot days my truck runs just over 210 (OEM gauge which I realize is not terribly accurate) with a 160 thermostat. For the record it never even hit 210 yesterday.
Those oem guages just show relative ECT (engine coolant temp). I believe that that the low end of the scale it doesn't start to move until the ECT is around 100F and at the high end of the scale it would be around 230 or 240F.

Under normal atmospheric pressure (rad cap off), the coolant would boil at 212F, but under 15psi rad cap (normal cooling system pressure inside the rad), it would could run as high as 230F in the red scale area.

The PCM can detect if the ECT sensor is running cold too long, and the ECT is out of range (input too low or too high) for PCM to deal with, but there is no real PCM determination of what is considered a "hot engine", because you change change thermostats from 160F all the way to 195F, so you have to rely on where the guage is. The ECT sensor sends the
signal to the PCM , which sends the ECT data to the instrument cluster controller to display on the dashboard guages.

So if your truck is running 210 with a 160 degree thermostat on hot days, you certainly appear to have a cooling issue.

Check out the thermostatic fan as well. The thermostat is a separate unit that bolts to the fan and is in front of the fan to sense the rad temp.

The way the thermstatic fan works is that there is a bi-metallic spring inside that finned enclosure and it senses the rad air flow temp.
If the air flow is above 175F to 190F (I believe), it will engage the viscous clutch inside the thermostatic unit and that that allows the fan to be driven by the engine serpentine belt.

If the rad cooling air flow is below 175, it disengages and free wheels, saving some engine horsepower.

To test the viscous clutch fan, spin it by hand when the engine is cold and not running obviously. If the fan spins more than 5 revolutions, then the thermostat unit needs to be replaced.


However, now that it seems it could be a factor in this issue, I should probably take a closer look at the radiator.
If you have a low temp thermostat and the engine is running hot..

some possible causes:
1. rad fins are loose and not providing sufficient cooling to rad cross tubes
2. rad is partially blocked with crud/corrosion from coolant being in there
too long. Old coolant turns acidic with time and will corrode the inside of
these aluminum radiators. Reverse flushing the rad may help and new
coolant needs to be added. This should be done every two years.
3. Rad pressure cap
4.Thermostatic clutch fan operation

I'm looking for a trans cooler now.
Thanks for the help!
It won't hurt to install a tranny cooler, as these are usually in front of the rad, and will get some airflow when the truck is actually moving, but you still may need to check out why the regular transmission cooling system (rad/thermostatic fan), doesn't seem to be adequate in your case.
 

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Discussion Starter · #7 ·
Check out the thermostatic fan as well. The thermostat is a separate unit that bolts to the fan and is in front of the fan to sense the rad temp.

The way the thermstatic fan works is that there is a bi-metallic spring inside that finned enclosure and it senses the rad air flow temp.
If the air flow is above 175F to 190F (I believe), it will engage the viscous clutch inside the thermostatic unit and that that allows the fan to be driven by the engine serpentine belt.

If the rad cooling air flow is below 175, it disengages and free wheels, saving some engine horsepower.

To test the viscous clutch fan, spin it by hand when the engine is cold and not running obviously. If the fan spins more than 5 revolutions, then the thermostat unit needs to be replaced.




If you have a low temp thermostat and the engine is running hot..

some possible causes:
1. rad fins are loose and not providing sufficient cooling to rad cross tubes
2. rad is partially blocked with crud/corrosion from coolant being in there
too long. Old coolant turns acidic with time and will corrode the inside of
these aluminum radiators. Reverse flushing the rad may help and new
coolant needs to be added. This should be done every two years.
3. Rad pressure cap
4.Thermostatic clutch fan operation



It won't hurt to install a tranny cooler, as these are usually in front of the rad, and will get some airflow when the truck is actually moving, but you still may need to check out why the regular transmission cooling system (rad/thermostatic fan), doesn't seem to be adequate in your case.
I checked out my fan today. It seems fine; it wouldn't even make a full revolution. In fact, it only moved a couple of inches.

I don't believe the radiator is clogged. I had all my fluids flushed in January after I bought the truck just to be on the safe side. I've put about 5000 miles on it since then. The coolant still looks good and the trans fluid looks fine.

The radiator cap is new (April-ish).

I'm thinking about replacing the radiator just to be on the safe side along with adding the trans cooler. Eventually, I'd like to replace the clutch fan with a thermostatically controlled electric unit.
 

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I checked out my fan today. It seems fine; it wouldn't even make a full revolution. In fact, it only moved a couple of inches.
Ok, so it's not the OEM thermostatic fan, which btw is setup to work with a 195 degree thermostat as most are equipped, at least where I live with the colder winter season we experience up here.
You mentioned that you have a 160 thermostat installed on your truck?
While that is probably more common in some high seasonal temperature environments, it only means that the thermo opens SOONER (than later as with the 195). Keeping it around those 160 degree temps requires a lot more cooling capacity.
The thermostat alone cannot do it's on it's own. It only helps to regulate the "normal operating temperature".
IF the heat of the engine can't be removed efficiently with air flow, (and lots of it), the coolant temperature will still
climb up well above 160.

However, if enough rad air flow + the clutch fan operation moves the air across the cross tubes/fins of the rad in cooler temperatures, it might be able to keep the engine at a lower operating temperature, but if the summer heat (or moving slowly in traffic), restricts air flow through the rad a lot, it will be a challenge for the cooling system to keep up.

To remove that built up engine you need to force more air through the rad and A/C condensor in front of the rad, so you still may have a cooling issue. If you are not moving fast enough to get sufficient air flow, very little heat is getting moved away the rad fins, (just through normal convection)..so all you have at that point... to help remove the excess engine heat IS THE FAN, (viscous clutch type or electric).


So if the viscous clutch fan doesn't come on until the engine coolant climbs up to 190 or more, the effectiveness of that 160 degree thermostat is very limited in keeping your engine and tranny cool.


I don't believe the radiator is clogged. I had all my fluids flushed in January after I bought the truck just to be on the safe side. I've put about 5000 miles on it since then. The coolant still looks good and the trans fluid looks fine.The radiator cap is new (April-ish).
Ok, so for the standard "2 row cross flow" rad, it looks like you are looking after it reasonably well.
But, it still may not be providing enough cooling capacity for the tranny fluid in certain circumstances.
Even though you had it reverse flushed, also make sure there are NO bug screens in front of it (on the A/C condensor
in front of the rad), as that will restrict air flow even more.

Now the other thing that is recommended for rad maintenance is to clean the dust/dirt off the fins of the rad (and A/C condensor unit) with a low pressure (garden hose)nozzle, (DO NOT USE A POWER WASHER!), and clean those fins as best as you can. Inspect them at the same time that they are tight against the cross tubes, you can do that by trying to move the fins with your finger..if they feel loose..time to replace the rad!

If the fins are corroded or loose, they will NOT transfer heat efficiently to the inflow air. That contributes to building up heat in both the engine and the tranny cooler side tank on the rad.

I'm thinking about replacing the radiator just to be on the safe side along with adding the trans cooler. Eventually, I'd like to replace the clutch fan with a thermostatically controlled electric unit.
Rads are very expensive, so check out the outside condition first. The engine will tolerate a lot more heat than
the tranny temp sensor, so if it was mine, I would do it one stage at a time.

Install the tranny cooler, because the additional cooling on the transmission fluid will definitely lower the internal temperature of the tranny and keep it working properly (preventing deterioration of the clutch band/band composite material and keep the SEALS inside the valve body from cooking at extreme fluid temperatures. A cooler transmission will
last longer and provide more troublefree service..(well other than perhaps the sensors.)

( Most aftermarket transmission coolers have bypass thermostats so that the fluid can get up to temperature faster in colder weather.)

Changing the clutch fan to an electric fan is a very good idea in hotter climates, because the electric fan will come on sooner and force more air to move through the rad fins and most electric fans are thermostatically controlled 2 speeds,
I believe. (The 4 cylinder Dakotas come with an electric fan instead of the viscous fan on the v6/V8, and there is a
provision for the fan relay and fusing in the PDC.)
 

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Discussion Starter · #9 ·
The radiator fins don't seem to be loose. I try to keep my truck pretty clean so I routinely spray the radiator and A/C condenser when I hose down my engine bay so no issues there. Since that is the case, there doesn't seem to be any obvious issues with the radiator.

I think my best course of action is to swap in an electric fan and add the trans cooler.

Thanks for all your help!
 

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I think my best course of action is to swap in an electric fan and add the trans cooler.

Thanks for all your help!
+1 on that decision. Those cooling upgrades will keep your 360 and tranny
very happy, and compared to tranny repairs, definitely a worthwhile investment if you plan on keeping it a while longer.
Those MoPar Magnum V8s are good old detroit iron..last practically forever.
 

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Ev, my brothers Indy truck did that on the way to the Mopar Nats. in 2003. It turned out to be the throttle position sensor. It would jump in and out O/D, freaked him out cause we were about 800 miles from home.
 

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Ev, my brothers Indy truck did that on the way to the Mopar Nats. in 2003. It turned out to be the throttle position sensor. It would jump in and out O/D, freaked him out cause we were about 800 miles from home.
Yes, every case is different. On your brother's DAK, the TPS sensor freaked out the PCM so it would do that, because it needs an accurate i/p of the throttle position for down shifts and upshifts on the tranny.

But I believe that on EvBaxter's Dak, it appears to be more of a transmission cooling issue, because otherwise he would have experienced other problems with idle and upshifts/downshifts. He mentioned it was intermittent and the transmission temp indicator was set by the PCM.

O/D on the Daks is controlled by the PCM, as it is responsible for the 3->4(O/D) shift solenoid,
into O/D (and conversely downshifts from O/D if the situation warrants it.)

A manual request can be entered to go out of O/D in certain cases, such as pulling a heavy load up a steep hill.
Eventually as the the vehicle speed drops off, the PCM would do that automatically, but the operator has the
option to disengage O/D at anytime. The PCM also controls the transmission relay in the PDC.

Sensors involved: transmission temperature sensor (thermistor)
Transmission output speed sensor
VSS (Vehicle speed sensor located in the differential), vehicle has to be above a certain speed (above 25mph)
for the 3->4 shift to take place, and of course,
the TPS sensor
 

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Discussion Starter · #13 ·
I hope to have closed the loop on this issue. I installed a Derale Series 8000 (D13503) auxillary transmission cooler yesterday. I was delayed due to not having the proper fittings to tap into the radiator and return line. The Derale online catalog recommended 9/16 adapter fittings, but it turned out to be 5/8 (which I was able to find locally at an automotive fastener shop). The bad part was that I had to disassemble it to make that discovery.:eek:

For those considering this mod, the lower transmission line on the radiator is a real bugger to get at. Other than that and getting the proper fittings, this was a pretty simple mod.:)
 
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