Transmission Temps Towing

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twscfltx

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Any advice on transmission temperature towing trailer up mountains? How do I figure out my truck/trailer limits / gradeability to avoid routes that would exceed my truck's limits.

2014 RAM 3500 DRW LB Crew
6.7L I6 / 68RFE 6-Speed
3.73 Axle Ratio
27,000 lb GCWR
19,000 Towing Capacity
Fifth Wheel: 16,000 lb GVWR

Last week I was worried about my transmission towing up a narrow winding 6% grade. The transmissions temp was 220F for maybe 10 mins and peaked at 226F. No warnings lights.
1200' climb over 3.5mi
2400' elevation
40F outside temp
~14,750# trailer
~750# in truck

1. The advice I received was to avoid 220-240F. Is that right? That did not seem like a serious climb to hit the transmission temp limits.

2. We maybe averaged 15mph. Would it have been better to go faster to increase airflow and maintain momentum? At the time, I thought I was helping by going slow. I maybe could have done 25 mph.

3. Are there more expensive transmission fluids ATF products that improve heat transfer?

Thank you,
Tyler
 
You may want to research the type of transmission fluid you have and what it is rated for.  You should also check the specs for the transmission.  I had similar concerns with my vehicle and feel much more confident after doing the research.
 
You really want to keep the RPMs up in the power band. Going slow may sound like the engine is working less but lugging creates much more heat and stress.
 
The biggest issue with these Dodge transmissions is they do not lock up the torque converter in second and third gear. Therefore you are running on pure fluid and it heats up real fast.

I'm having a BD Tow/Haul transmission installed in my 2006 Dodge Diesel next week. These "built" transmissions lock up in all gears so you are not spinning on fluid when pulling up a long hill.

The various Doge foruns show how to install a simple switch to lock the torque converter in the lower gears. You just need to remember to unlock it when coming to a stop.

As far as temperature, it all depends on where it is being read. You might want to check some of the Dodge diesel forums for a better explanation of this.

220 degrees can be no issue in some areas of the transmission and a cause for concern in others.

I read the transtemp in my 2006 through a Juice with Attitude tuner and it reads from the OBD connection. On a few really long pulls I've seen 260 degrees for upwards of 15 minutes......YIKES! And I'm only pulling 9,000 pounds.....
 
I had the same problem with my Ford diesel.  I added a rather large transmission cooler in front of all the other radiators so it got the coolest air and best flow.  This was in addition to the other two coolers For put on it.  Never had a problem after that.  I towed a 12,000# fifth wheel.
 
Can I get the torque converter to lock in 2nd or 3rd? What speed would that be?
 
keymastr said:
You really want to keep the RPMs up in the power band. Going slow may sound like the engine is working less but lugging creates much more heat and stress.
Click to expand...
He's got a diesel, not a Hemi. Best pulling is around 2,200 to 2,800 rpms. With a Hemi, between 3,600 to 5,500 rpm.

If you are worried about heat. Install another tranny cooler. I did. Goggle atf temperatures. Bunch of charts. If you go over 240F for any length of time. Change your fluid.
 

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Do a search....There is a simple wire that you cut and add a switch that keeps the torque converter locked in any gear. You just need to remember to shut it off when coming to a stop as the truck will stall or you'll hurt your leg standing on the brakes trying to stop the truck (Diesel especially)

Some folks have installed a switch under the brake pedal to disengage whenever the brake is applied.

It is not an elegant solution, but lots of folks hauling big trailers on back roads are doing it.

Depending on the year and make of the truck, BD Diesel offers devices that accomplish this much more elegantly.
 
The transmission fluid dip stick looked clean. I'm still trying to figure out what routes I can take without watching my trans sump temp the whole time.

Please give advice to compare aftermarket options:
Deep pan vs Cooler
 
Coolers are more efficient, cheaper, and easier to install.  But they don't look as cool as a deep finned aluminum pan.

Put your hand near (not on) your rear diff cover after a long pull.  (It will be hot!). That's where you probably need the aluminum fins.
 
Is it better to install the cooler underneath adjacent to the transmission or upfront in front of the other coolers?

Would an auxiliary transmission cooler make a significant difference for a 68RFE towing 16,000#?

This does not change the heat generation. Should I consider options to manually lock up the torque converter in 2nd and/or 3rd gears? What are the risks? Is this a DIY project? Does it void powertrain warranty? Does it require reprogramming tuner?

Thanks again.
 
If the additional cooler is installed in front of the radiator and charge air cooler (intercooler) in a turbocharged engine that's probably all you need.  Installing it underneath limits the airflow unless you put a fan behind it to suck air through it.

In my opinion the first option works better, less expensive, and the cooler won't be exposed to road grime, rocks etc.

I never found it necessary to modify the torque converter lockup. 
 
Does the aux Tran Cooler need the thermostat sensor or should I just run it all the time?
What is the best terminal for power supply?
 
Good question. 

If you install a cooler and the transmission never warms up you might need a thermostatic valve.

Some transmissions have them built in.  Some don't.
 
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