6.7L I6 / 68RFE Transmission Temp Towing

[twscfltx]

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
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 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?


I would have loved to have found a used 1 ton DRW with heavy duty trans and 4.1 ratio, but I could not find any used.


Thank you,
Tyler

 

[jelag]

I have the same concerns.... however my 2013 3500 has the 3.42 ratio....

 

[spoon059]

The truck will defuel before it allows harmful temps. I wouldn't worry about excess temps. Just curious, was your trans shifting gears and locking/unlocking the torque convertor a lot during the climb? That is usually what causes the temp spikes. If your trans is hunting, you might want to simply manually select a lower gear for the climb and keep it locked in.

 

[JDean]

I have the same year drw truck, same rear end, tow the same weight. For as long as I've owned this truck, I've displayed the transmission temp on the EVIC, but as an analog gauge so I'm not sure I would notice a 6 degree temp difference. I have never seen the transmission temp even move, and I tow a lot as a full timer. Most boring gauge on the entire display, but I had so much trouble with transmission temperatures on my last truck (a 2007 drw 48re with the factory tow package, same trailer) that I'm always watching it. I've pulled the trailer up Wolf Creek pass in southern Colorado (which has up to 8% grades) twice and maintained the speed limit the whole time (so 35 to maybe 55 I think). It's actually more exciting going down, but the auto exhaust break helps a lot.
Just pulled from Pahrump to Las Vegas today on our way to Lake Havasu City. Long steady climb at maybe 4 - 6% (which I think can be even harder on transmission temps than short steep climbs) and still didn't see any movement on the transmission temperature. Can't imagine slowing down to 15 mph on a 6% grade. Maybe you're being too nice to your truck. I always try to tow with cruise control (with t/h and auto exhaust brake) with this truck and let it do all the pedaling.
- John D

 

[sag2]

Your problem was the transmission was not in high enough gear to have the converter locked. Unless you had a lot of switchbacks to keep the speed down it should have easily pulled it in a higher speed in a higher gear. According to my info the converter should lock in 2nd-6th but it could be 3rd-6th.

 

[Hoefler]

Your problem was the transmission was not in high enough gear to have the converter locked. Unless you had a lot of switchbacks to keep the speed down it should have easily pulled it in a higher speed in a higher gear. According to my info the converter should lock in 2nd-6th but it could be 3rd-6th.

This is correct. I learned it on my 08. Road so rough from a temporary detour running through the Big Horn Mountains. Was unable to go any faster than 7-10 mph pulling our 5ver, shifting back and forth from 1st and 2nd, wound up pegging my gauge at 285*. Stopped and shifted into 4wd low, was able to get the transmission to lock up in 5th, the temp came back down to 200* with in a mile and stayed there the next 12 miles until we hit pavement again. The rest of the trip we stayed on good road, and the temp stayed around 195*-205*.

 

[twscfltx]

This is correct. I learned it on my 08. Road so rough from a temporary detour running through the Big Horn Mountains. Was unable to go any faster than 7-10 mph pulling our 5ver, shifting back and forth from 1st and 2nd, wound up pegging my gauge at 285*. Stopped and shifted into 4wd low, was able to get the transmission to lock up in 5th, the temp came back down to 200* with in a mile and stayed there the next 12 miles until we hit pavement again. The rest of the trip we stayed on good road, and the temp stayed around 195*-205*.

So I need to try maintain steady RPM at higher gear i.e. go faster. The switchbacks were tight, but I should have been able to do 25-30 mph.
Should I put it in 2nd or 3rd rather than drive?
Should I have the exhaust brake on towing uphill?

Does anyone know where the sensor is on 4th Gen 3500 Tradesman? I'm guessing the inlet to the trans cooler up front.
What is the recommended temperature limit? 220-240F?

 

[Jim W]

Depending on road conditions, my 08 with the 68RFE will never exceeds 190F trans temps and this was through the Eisenhower tunnel on I70 pulling my 2016 34RL Cedar Creek. I usually will pull in 6th gear but will drop to 5th as needed, watching Boost pressure, EGT's and transmission temps. I do have a Mag-Hytec deep dish oil pan on the transmission with a temp probe in the pan.

I never use the drive selector on my truck. I will always place the toggle selector in some gear usually locking out 5th and 6th gear in town and will shift up a gear as needed when the speed limit increase,even when towing. I also use the tow/haul mode when towing my 5er. I try and keep the RPM range between 1500 and 2000 RPMS max. My differential gearing is 3:73 and I am using stock tires size 17". So a fourth gen with 3:42 and 18" or 20" tires will have a slightly different RPM range at different speeds than my truck. Find what is best for you.

I always run the exhaust brake on my truck this will keep the turbo from sooting up. I start my truck and than turn the exhaust brake on. I have been driving the truck this way since new and I still have the original Turbo at 102,400 miles.

Check for a thread on this forum by TRANS Engineer he has put out a table on transmission temps for the 68RFE.

 

[Cummins12V98]

I NEVER saw temps 200 or over towing 29K in temps up to 100 and grades up to 6%. Hold the pedal to the floor and let the truck do the work. NEVER go into 1st unless you have to. 2nd and up it will lock and maintain good temps.

I do not believe the engine will de fuel if the trans gets over 200.

 

[kthaxton]

I recall transengineer stating that when climbing very steep grades slowly, that you should be in 1st gear as there will be less difference in rotation speed between the engine and trans....thus minimizing heat buildup from torque converter slippage. Of course, he had a lot of data and a more detailed explanation than I am providing.

 

[twscfltx]

Can I get the torque converter to lock in 2nd or 3rd? What speed would that be?
=

 

[sag2]

As I said the information I referenced last night said locks in second up, but it was generic RFE not specific to 68RFE. That is why I said second or third. If you could have got it into second and held the speed you would have known quickly if it was locked as the temp would have come down quickly. To avoid what you had happen the speed isn't as important as the gear selection. As long as you can keep it in a locked up gear don't worry about the RPM or speed.

 

[twscfltx]

As I said the information I referenced last night said locks in second up, but it was generic RFE not specific to 68RFE. That is why I said second or third. If you could have got it into second and held the speed you would have known quickly if it was locked as the temp would have come down quickly. To avoid what you had happen the speed isn't as important as the gear selection. As long as you can keep it in a locked up gear don't worry about the RPM or speed.

Since locking up depends on gear and speed, I'd like to know what the lowest speed would lock up towing 16000#. I'd use that speed to compare to listed speed limits to judge what routes I could take.

 

[EDankievitch]

I've only seen slightly higher trans temps once stuck sitting in traffic on the BQE the temp got up to 210. Dropped out of drive and allowed the engine to spin up a bit and the temp dropped right off really fast. Towing even heavy loads in 6th I never see the temp rise above the normal unloaded temp. So my advise unless your stuck in traffic on a really hot day not moving for an hour or two just drive and enjoy the fact that the cooling system is nicely over built.

 

[transe]

The bottom line is:
• If the TCC is locked, your temps should be OK.
• If your TCC is not locked (or won't stay locked), then drop it down (manually) to a lower gear (so hopefully, the TCC can lock and remain locked).
• If your TCC won't stay locked up in 2nd gear, then drop it all the way down to 1st gear. The TCC will not lock in 1st gear, but running in 1st gear unlocked gives you MUCH less heat than running in 2nd gear unlocked.

 

[jelag]

Additional Question Please.....

I now have 600 miles on my new to me.... 13 Laramie Longhorn... I'll get the truck home next week.... I've already ordered some parts from Geno's but need to ask this question... is the transmission filter serviced from the outside of the transmission... or does the pan have to be pulled down to service this.... this of course would be self answering if I could crawl under the truck...

BTW this is by far the best driving Dodge 3500 I've ever owned..

 

[SnoKing]

BTW this is by far the best driving Dodge 3500 I've ever owned..

We told you so!!!! SNOKING

 

[jelag]

OMG go ahead and rub it in..... I've got broad shoulders and can take it.... we'll have the real answer next spring when we tow.... what about the spin on filter.. now that you've teased me..

 

[Jim W]

You have to remove the pan to get to both filters, at least on my 2008 Ram with the 68RFE. I change the fluid and filters every 40,000 miles.

 

[SnoKing]

OMG go ahead and rub it in..... I've got broad shoulders and can take it.... we'll have the real answer next spring when we tow.... what about the spin on filter.. now that you've teased me..

I use Fleetguard filters and Ron's (Cummins12V98) from the top routine. Bought a 28 MM 6 point 1/2'" drive socket for fuel filter cap and the water sensor wrench. I use a strap wrench for the oil and chassis mounted fuel filter.

https://www.turbodieselregister.com...-2013-and-up-oil-change?p=2439304#post2439304


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