2917 w/68rfe trans

[Viper1]

I have a 2017 Cummins with a 68rfe transmission. I am pulling a 5th wheel and total weight of both is 23675 lb. I bought the truck never thinking I would own a 5th wheel but life has its turns. Here is my question, last week the weather was very warm and my Tran temp went to 217, is that too high? Engine temp stayed about 208-210 with my oil temp going up to 215. This was in slight grades. All cooled down in flats. I would, at this point hesitate taking some real hills. Is there any thing that can be done to this transmission without going out of warranty i.e., shift kit, coolers etc. or any good suggestions to improve or maintain pulling abilities.

 

[Ozymandias]

That you use TH and EB On all Time pulling your 5th is set yes?

 

[Wiredawg]

I only have experience with the Aisin, but there are a few things to do: TH like Ozy mentioned, manually downshift the transmission, and slow down, as is mentioned in many operating manuals. On my 09 4500, I added an aux transmission cooler with thermostat controlled electric cooling fan. Adds more transmission fluid and gives extra cooling under severe conditions. I mounted it on the back of the cab.

Cheers, Ron

 

[TFucili]

Was the torque converter staying locked? Was it pulling in 6th gear? I can't speak to the 68RFE directly, but I am pulling at a bit over 23K combined with a 6.4 gasser and 66RFE, the "step-brother" of the 68(kinda sorta). I don't recall my trans temps getting above 172-174 even with the gasser screaming in second gear with the converter locked. Hopefully others with your combo chime in.

 

[EZeis]

Maybe the cooler thermostat valve stuck? Heard they have issues with those sticking on the 68 and Aisin. It's a thermostatic valve that regulates the flow to the cooler(s) to maintain temp, especially in the cold. The temp you posted seems high to me. I'm not trans expert but I'd be concerned too.
A performance company makes a bypass for the thermostat valve. Unfortunately it eliminates temp regulation completely giving constant flow to the cooler(s). I'd be concerned in cold winter states that the trans gets up to temp.


Earl

 

[Jim W]

What gear were you in and what engine RPM's were showing on the tach?

I have an 2008, with the 68RFE auto, towing a 34RL Cedar Creek with a combined weight of 21,000 LBS, scaled.

I normal see 195F at the transmission oil pan from my temp probe in the pan, ambient air temps are around 80 to 90F. I see this temp all of the times when I am towing in the mountains. But I am in 5th gear, engine RPM'S around 1900 and I am doing about 55MPH with the T/H button pushed and the exhaust brake is on. I do have extra oil in my transmission, 3 qts and a deeper transmission oil pan on my truck, it is a Mag-Hytec Al pan.

As a general rule automatic transmission oil temps will start to fail above 275F.

 

[kthaxton]

I'm with EZeis, I bet the bypass is stuck.

The only time I've had my trans get much above 170 is when I had to take a detour and had to climb a steep grade in bumper to bumper traffic. Never an issue on grades when I keep moving and the TC stays locked.

 

[Cummins12V98]

NEVER seen any temps that high even on 6% grades at 100 degrees combined 29k 2011 HO 68RFE with 3.42's. Stop and go it would go over 200.

This pic was towing on flat ground and 172 was a normal temp. Climbing a grade did not change much.

 

[jelag]

I tow about the same weight... I've never seen the temp that high on my 2013 with the same transmission.... I always use TH and the exhaust brake even when I don't tow.... I don't think I've seen 200 degrees....

I did change the fluids, both the transmission and diff to a full synthetic and will continue to change it more frequently....

On another note reading a Allison Manual for the 3000 transmission..... they believe that using an exhaust brake or engine brake constitutes sever duty and requires a full synthetic fluid as well as changes much more frequently...

Just my thoughts...