Hey guys....
Been reading for years but never posted. The problem I have started the first time I pulled my 5000lb trailer with this truck. It's a 2006 Dodge 2500 crew cab SB, Cummins 5.9 with 200000 on the clock. Bought it about 4 years ago but had never towed with it. It's never had an overheat issue until now. The first 2000ft grade the trans overheated to the point of the idiot light coming on...260° from what I'm reading. Engine temp was at a at 220° ( yes I was in tow/haul and torque was locked ). Fan clutch right ? Nope had the fan and water pump changed by a Diesel Mech. It overheated again!
Had a masimoto cooler installed in case the old original OEM was plugged. Changed all fluid and filter.It helped immensely but it overheated again. Had the transmission rebuilt.....it over heated again!! Bought a scangauge OBD2 for the gauge functions and low and behold I think I found the problem.
The fan clutch runs when the coolent temps reach 210, it also runs when the AC is on but it NEVER comes on for high trans temps. It'll run until coolent is back to normal but stop long before trans fluids are cool and no matter how high they climb it never comes on. The ECM sees the temp.
ANSWERS ANYBODY ? About ready to trade it in.

 

Put a fan on the cooler for the trans? I know they make them.

 

Hmm...
I wonder if the fluid is flowing unobstructed thorough the transmission cooler.

I am not familiar with your truck engine transmission BUT, when I rebuilt my Chrysler A-604, I remember one part that I changed in the Master parts kit was a transmission fluid thermostat, just like a radiator thermostat, it is to restrict trans fluid from flowing through the cooler until the transmission gets up to operating temperature...

Just throwing that out for consideration

 

rebuilt nm

or rebuilt what parts source and was the thermo included in parts

 

Thanks for the response.
The Mosimoto transcooler comes with a removable thermostat and that has been removed. I haven't been able to find an answer to this question......is the electronic fan clutch controlled by trans temps ? Obviously it is by coolent and AC but trans temps is an unknown.

 

I think I should find the reason for the heating issue first. It doesn't overheat unless im towing. Friction or an obstruction is going to shorten my trans life even if i manage to keep it cooler. BTW I had a P1740 code pop-up today while accelerating onto the freeway.

 

Sounds like you've lost lockup. It could be the solenoid pack or the TCC its self.

 

I'm just driving this old Dakota with mechanical fan clutch and I've never had a diesel, so bear with me if I say anything silly. So you have an electronic fan clutch triggered by coolant temp, but you're reading high tranny temp? Now on my truck, I have a factory external tranny cooler but the coolant passes through the radiator as well. Is yours supposed to be that way? Did you/someone uncouple that to make it rely on only on the cooler?

 

Like I said previously, there is some sort of thermal (mechanical) transmission thermostat that stops the oil cooler from circulating until the transmission gets up to operating temperature.

I googled
545RFE transmission thermostat
and sure enough, sometimes it fails and get stuck in recirculation mode.

Symptoms:

• Overheating
• Overheated fluid

Cause:

The thermal bypass valve in the OE cooler bypass valve can become stuck in the cooler bypass position, causing hot fluid to circulate in the transmission that leads to overheating.

** It looks like this valve block may (luckily) be external to the transmission AND I would get a replacement thermal valve and NOT THE SONNAX BS CHEAT PART unless you never expect tooperate in cold climate...

Please let us know what you find and how you fix it.

PS, in MY a604 transmission from my minivan, I would have to remove the transmission and open the cavity to change this part.... so you area lucky if this is external..

 

We're all just going to casually ignore that he's got a code for a malfunctioning TCC? If he doesn't have lockup he'll overheat in no time towing.