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Discussion Starter #1 (Edited)
About a month ago, I picked up my very first Dodge — a neglected 2002 Dakota SLT Club Cab 4x4 with the 4.7L V8 SOHC engine, 45RFE tranny, and 104,000 miles on the ticker. While performing a major tune-up, I made an incredibly alarming discovery — the previous owner had cut both transmission oil cooler lines just under the crankshaft pulley and connected them with rubber hose, "capping" the system upstream of both the built-in ATF heat exchanger within the radiator as well as the auxiliary oil cooler and effectively robbing the transmission of any ability to shed heat.

Despite performing a comprehensive examination of the vehicle before purchase, I was not familiar with the Dodge 4.7L V8 / 45RFE builds or the transmission oil cooler line routing and missed identifying the closed-loop system due in part to the fact that the downstream portions of the severed hoses were routed and supported over the front frame cross-member. I pulled the upstream portions of the cut lines down into a relatively normal position for sake of the below photo:
2020-02-10 2002 Dodge Dakota Transmission Oil Cooler Lines Cut 004.JPG


2020-02-10 2002 Dodge Dakota Transmission Oil Cooler Lines Cut 001.JPG

The transmission behaved fine during the 1 1/2-hour commute home over flat terrain, although I did baby it at about 50 MPH due to the engine running rich on account of a bad O2 sensor. Other than the drive home, I haven't yet put the truck on the road while I finish up some engine-related repairs. I had no reason to suspect a damaged transmission until discovering this modification while familiarizing myself with the transmission components per the service manual.

I had planned to use this truck for business-related light towing duty (3,000–4,500 lb. gross trailer weight), and was hoping it would become a reliable asset after my tune-up. But I know that heat is a transmission's #1 enemy, and this unwelcome discovery regarding the cooler lines has me very concerned regarding the condition of this transmission and my ability to rely on the truck moving forward. At this point, I'm trying to figure out how to best evaluate the condition of the transmission and identify the extent of how much damage it may have suffered.

For sake of reference, the Factory Service Manual states that the normal transmission fluid operating temperature is 180° F. I've read that the "Trans Temp" warning light on the cluster will come on if transmission fluid reaches 260°F, at which point the PCM will force the transmission out of Overdrive in an attempt to save it from further damage. This will be indicated in both RPM's and by the "O/D Off" light on the cluster coming on. The PCM will re-enable Overdrive when transmission temps drop to 230° F. or below.

Here's a summary of what I know:
  • The transmission fluid dipstick indicates the fluid is full, of a bright pink color, and doesn't smell burned
  • The transmission appeared to operate without issue while driving the truck home, with no signs of slipping, delayed shifts, or hot/burning odors
  • The "Trans Temp" warning light on the cluster has not come on at any point while driving the truck
  • The "Trans Temp" warning light on the instrument cluster is working, as it lights up when turning the key to "On"
  • The "Overdrive Off" light on the cluster has not come on automatically at any point while driving the truck
  • The "Overdrive Off" light on the cluster is working, as it can be toggled on/off via the switch on the end of the gear select
  • The rubber hose used to connect the supply and return transmission oil cooler lines looks relatively new
  • The ambient air temperature during the drive home was approximately 35° F. according to Weather History reports, which may have helped lower transmission temps
  • The rubber splash shield that usually shields the underside of the engine bay is missing, potentially contributing some airflow to the oil cooler lines that would otherwise be non-existent
The above data points would appear to offer some hope that the transmission is not unduly damaged. However, I've read many accounts of the 45RFE transmission overheating and promptly dying as a result of the plastic ball in the check valve located in the transmission oil cooler line which routes ATF to the radiator getting plugging with debris or melting due to high temperatures. This is the problem that the "Check Valve Delete" mod is intended to proactively prevent.

If a restriction in one cooler line like the aforementioned check valve has the ability to overheat and kill the 45RFE in short order, how could a closed-loop system like mine possibly be any better? Is the difference simply the fact that the fluid is still allowed to flow, as opposed to being bound up by a jammed check valve? Do the hard transmission oil cooler lines receive enough airflow to relieve just enough heat from the fluid in the current configuration?

After reading up on the stock transmission oil cooler hose routing and overall fluid flow throughout the 45RFE transmission system, I'm quite puzzled as to why the lines would have ever been cut and capped in such a way to begin with. A few possibilities come to mind, which I've listed in order of what I believe to be most to least likely:
  1. Auxiliary Transmission Oil Cooler was/is leaking
  2. Transmission fluid heat exchanger contained within the 18-year-old original radiator was/is leaking
  3. Transmission oil cooler lines were leaking downstream of the modification
  4. Torque Converter Anti-Drainback Check Valve became plugged / melted
None of the above are major, complicated, or expensive repairs that would make the chosen modification to the oil cooler lines seem like a good alternative. The possibility of the #2 scenario above scares me, as in such a case the coolant may have cross-contaminated the transmission fluid, complicating matters even further. I attempted to pressurize the radiator to rule out an internal leak, but couldn't find the right adapter for the radiator fill neck.

I may end up simply replacing the transmission oil cooler lines, auxiliary oil cooler, and radiator all in one fell swoop to ensure I have a properly-functioning system. But before I go that all that time and expense, it would be nice if I could figure out whether or not the transmission has been seriously damaged. I do have plans to drop the transmission fluid pan and replace both ATF filters as part of my tune-up, so I'll have a chance to examine the pan for signs of overheating or damage at that point. However, I would prefer to repair / replace the capped transmission oil cooler lines and flush both them and the radiator and auxiliary transmission cooler with the current filters in place before replacing them.

Prior to discovering this nightmare, I had planned to obtain and install an aftermarket transmission temperature gauge to keep an eye on transmission temps while towing. Before deciding how to proceed with the truck, I'm considering obtaining and installing such a sensor and gauge on the current system as configured and checking to see what temperature the transmission is currently operating at to get a feel for how much heat stress it may have undergone due to the current setup.

The questions I have for those with experience with the 45RFE are as follows:
  1. What do you think is the most likely explanation for the current setup?
  2. How likely is it that the transmission is somewhat damaged, and to what extent?
  3. Is it possible for the current setup to adequately cool the transmission fluid, at least in conditions and temps like my commute home?
  4. What is the best way for me to test the transmission and get a feel for its current condition?
Any and all insight would be greatly appreciated.
 

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99% odds that it was capped because the internal cooler in the radiator began leaking. That’s almost always the reason why someone does this.

Replace the radiator, restore it to normal fluid operation through the auxiliary cooler, and things should be fine.

If they didn’t tow with it... the transmission is likely fine. The fluid will tell you most of that tale. Is it excessively dark and does it smell burnt?
 

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Discussion Starter #3 (Edited)
99% odds that it was capped because the internal cooler in the radiator began leaking. That’s almost always the reason why someone does this.

Replace the radiator, restore it to normal fluid operation through the auxiliary cooler, and things should be fine.
Ugh — Although I figured either a radiator or auxiliary oil cooler leak were the most likely potential causes, an internal radiator leak was what I wasn't hoping to hear, as I have the hard-to-find "Max Cool" two-row, 1.5" core radiator that is 3-4x the cost of the standard one-row, 1.25" core unit. I also don't know what effects fluid cross-contamination between the two systems may have had if the radiator was allowing them to mix... although they can't be good.

Which coolant system typically runs at a higher pressure — antifreeze, or transmission fluid? I'm trying to wrap my head around whether antifreeze would have been making its way into the transmission fluid in the event of a leak, or vice versa.

Based on the manufacture date, the radiator is original to the truck (18 years old), so I would think an internal leak is certainly possible. I did disconnect the lower transmission oil cooler hose from the radiator and ran the truck for awhile to see if any antifreeze would come out, but none ever did. I may have to keep looking for a radiator neck adapter that will allow me to better test the system.

If they didn’t tow with it... the transmission is likely fine. The fluid will tell you most of that tale. Is it excessively dark and does it smell burnt?
The transmission fluid is currently nice and bright, with no signs of a burnt smell or foaming that could indicate coolant contamination. That said, the previous owner did mention having just towed a jet-ski about 50 miles. He also claimed he had just dropped the pan and changed both transmission filters. However, the pan bolts don't show signs of recent removal, and the pan gasket looks like it hasn't been disturbed in a long time. At this point I'm not taking anything the man said at face value, since he clearly lied to me on multiple accounts as I was discussing the vehicle with him prior to purchase.

Last but not least, I have also located another possible piece to this puzzle — the hard transmission oil cooler line that connects from the upper port on the radiator to the upper port on the auxiliary transmission oil cooler looks like it has had a section cut out and replaced with (again, relatively new) rubber hose, although I can't figure out a possible motivation for this other than a leaking hose:
2020-02-10 2002 Dodge Dakota Transmission Oil Cooler Lines Cut 006.JPG
 

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I was in the same shoes as yourself. I elected to mount a huge $100ish stacked-plate cooler in front of the radiator and entirely bypass the in-radiator transmission cooler. Mounted it on a couple of brackets I welded up to hang it in front of the rad and A/C condenser.

I ran an aftermarket temp gauge, and with a fully loaded car hauler trailer in 100* temps, I couldn’t get my trans fluid above 180. It worked great.
 

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Discussion Starter #5
Those transmission fluid temps are very impressive given the load and ambient temps! Sounds like that aftermarket cooler did the trick.

I'm a bit reticent to bypass the radiator completely, as I have read that part of the purpose behind the ATF fluid heat exchanger within the radiator itself is to not only cool the ATF, but also warm it during cold starts. The PCM disables O/D until the ATF has warmed to above 50° F., I'm assuming the radiator heat exchanger would help the ATF get to that point a bit earlier here in Michigan than it would otherwise.

One additional question that has come up as I've been pondering my issue — if the ATF heat exchanger within the radiator had started leaking, how would it manifest? I'm trying to figure out what would have flagged the previous owner that there was even an issue in such a scenario, as it seems like the problem could remain hidden for quite some time.
 

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Discussion Starter #7
Right — but what would have triggered the previous owner that there was a problem? Inspecting coolant and transmission fluid on a frequent basis isn't super common, and this individual hadn't even kept his windshield washer fluid reservoir from going bone-dry.

Just trying to figure out how he would have found out that the radiator was potentially leaking internally and known to cap the lines.
 

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Discussion Starter #8
Another question, as I've considered how to definitively prove or disprove whether my radiator has an internal leak between the coolant and transmission fluid heat exchangers — anybody know the typical pressure of the transmission oil cooler lines?

I have access to a radiator pressure tester kit, but it's recommended to only pressurize the system to typical coolant pressures of >20 PSI. If the transmission oil cooler line pressure is typically much higher, I could theoretically pressure test the radiator at the fill neck and have everything check out despite there still being a leak.

Open to ideas on how to verify the condition of my current radiator.
 

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Don't over think it.
Put on a new trans cooler.
If you do not have a radiator that has the fittings for the transmission fluid holes, ignore that part.
Plumb the cooler in.
Top off the fluid to the correct level for the added volume of the cooler.
Drive it.
At some point, drop the pan and change the fluid and two filters.
Move on with life.
 

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You're over thinking this. You bought it so it's to late to think about complicated scenario your presenting. The answers are simple as another person posted. It more than likely had a visible leak & the dude wanted a quick fix. Happens all the time.change the radiator with the poem if possible. I personally pulled a camper with my 02 durango for work. Had a tech put on an auxiliary cooler coil because it was an unusually hot summer and I didn't want to take any chances with my money maker's, trailer& durango. Cost me about $120 installed& never had a problem. I did however change the radiator& tranny lines prior to that because I check everything before I hit the road. If it looks original& badly rusted it got replaced before I hit the road. If it shifts fine just do the obvious& be glad you found one that old with the mileage you stated.
 
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