Transmission Temp Question

[jacknife]

Have 2014 3500 68 rfe transmission . going up 7% grade 80 deg out grade 3 miles long hauling 5th wheel 12000 lbs . transmission temp got up to 204 deg is this normal or within specs ? A response would be appreciated.

 

[Terry Jay]

Sounds normal to me. I usually run around 180 empty in temps in the 40's and around 200 pulling 15000 and temps in the 60's 2012, 68rfe, 3.73 4wd drw.

 

[Hoefler]

In my 08, I had the transmission temp peg my 285* gauge with no ill affects.

 

[transe]

In my 08, I had the transmission temp peg my 285* gauge with no ill affects.

OUCH! Are you talking trans sump temp (not "to cooler" temp)? That is WAY too hot, and consider yourself fortunate if you haven't seen any issues from it. I presume your "Trans Temp" light came on?

I would advise keeping your sump temp at 230°F or below. The cooler, the better. Once it goes over 230°F, start looking for a place to stop and cool down. Brief spikes over this are not a problem (you can indeed hit 240, 250, 260, even 270° for brief periods, without instantly killing your trans), but you don't want to run for extended periods at these levels.

 

[jacknife]

transmission temps

Thanks for the info. I was reading the temps off of oem gauge in dash. Where the the sensor is l do not know.

 

[transe]

Thanks for the info. I was reading the temps off of oem gauge in dash. Where the the sensor is l do not know.

OEM trans temp is read from a thermistor inside the solenoid module, so that is sump temp.

What were you doing, to get it up to that kind of sump temp? Some advice: (1) Don't do that again! (2) I'd suggest that you change your trans fluid.

 

[jacknife]

Only have 2500 miles on truck. transmission usually in 170-180 range empty. I was hauling a 13000 lbs 5 th wheel up 7% 3 mile grade. No warnings came on.

 

[Jim W]

Only have 2500 miles on truck. transmission usually in 170-180 range empty. I was hauling a 13000 lbs 5 th wheel up 7% 3 mile grade. No warnings came on.

That does not sound bad to me for your truck and pulling that size of a load for the transmission temp (204F).

On my 08 when stock with the stock pan I saw higher temps when pulling a 10K 5er out and back to South Dakota about 210F. I even saw 220F once on the Needles Highway RT 87 without the camper; we were descending the mountain grade using the transmission and exhaust brake in Custer state park. These are sump temps.

I have since installed a Mag-Hytec oil pan on the truck with the probe in the pan and only have climbed once to 200F, pulling my newer 5er (11K) in WY when we went to Yellowstone NP and than in to MT.

Jim W.

 

[sag2]

The 2014 1500 Hemi has a transmission heater that keeps the transmission at least 180-185, and many times right at 200 towing without working it at all. The heater was added to get the fluid thin quickly for added fuel economy.
I would not give your 204 a second thought. That being said if you want to keep it cooler than warmer use tow haul and try and keep the converter locked at all times by selecting the correct gear.

 

[transe]

OEM trans temp is read from a thermistor inside the solenoid module, so that is sump temp.

What were you doing, to get it up to that kind of sump temp? Some advice: (1) Don't do that again! (2) I'd suggest that you change your trans fluid.

Sorry, I thought I was replying to Hoefler (Mr. 285°F). Jacknife's 204°F sump reading is not a problem at all. Sorry for the confusion!!

 

[Ram4Sam]

Not hijack this thread too much....... Question for Transengineer? Is there anything to be gained from shifting these new auto trans into neutral when sitting at an extended stop light,versus sitting there in drive as far as keeping the trans a little cooler? I haven't owned an auto in years, an old habit I have from the old days......

Sam

 

[transe]

Not hijack this thread too much....... Question for Transengineer? Is there anything to be gained from shifting these new auto trans into neutral when sitting at an extended stop light,versus sitting there in drive as far as keeping the trans a little cooler? I haven't owned an auto in years, an old habit I have from the old days......

Sam

Sam,

Yes, indeed. Shifting the trans to Neutral when stopped at a light will definitely help to keep the trans cool. In Drive (at a stop) you are generating heat in the converter, due to the speed difference between the engine (idle speed) and trans input (zero speed). If you shift to Neutral, the trans input spins up to almost match the engine RPM, so you have almost no heat generated.

 

[Ram4Sam]

Sam,

Yes, indeed. Shifting the trans to Neutral when stopped at a light will definitely help to keep the trans cool. In Drive (at a stop) you are generating heat in the converter, due to the speed difference between the engine (idle speed) and trans input (zero speed). If you shift to Neutral, the trans input spins up to almost match the engine RPM, so you have almost no heat generated.

Good to know.....Thanks for the info.

Sam

 

[Hoefler]

OUCH! Are you talking trans sump temp (not "to cooler" temp)? That is WAY too hot, and consider yourself fortunate if you haven't seen any issues from it. I presume your "Trans Temp" light came on?

I would advise keeping your sump temp at 230°F or below. The cooler, the better. Once it goes over 230°F, start looking for a place to stop and cool down. Brief spikes over this are not a problem (you can indeed hit 240, 250, 260, even 270° for brief periods, without instantly killing your trans), but you don't want to run for extended periods at these levels.

To the cooler temp, trans light was on. Took it to the dealer afterwards, they checked it, DID NOT change the fluid, it was not discolored or smelled any different from new fluid. Drove it another 40,000 miles with out issue.

 

[transe]

To the cooler temp, trans light was on. Took it to the dealer afterwards, they checked it, DID NOT change the fluid, it was not discolored or smelled any different from new fluid. Drove it another 40,000 miles with out issue.

OK, if your 285°F was "to cooler" temp, then you can relax. That is not unusual for a grade climb situation at low speeds. I'm sure your sump temp was much cooler.

I would stop and cool down (or manually downshift to a lower gear) in order to keep your "to cooler" temp below 300°F, if possible.

 

[mpaulson]

In my 08, I had the transmission temp peg my 285* gauge with no ill affects.

I to have seen 285 on my 07.5 with the 68RFE three different times. This was line out temps. The truck had 230,000km's on it when I sold it this summer and never had the transmission touched other than annual spring time filter and fluid changes. This was during long off road pulls at very slow speeds, 5-20 km's/HR, with the quads on the truck and the 30' RV behind. This is one of the reasons I put free spin hubs on the truck so I could use 4x2 low range which would get the truck into 3 and 4 gear and lock up the converter.
Normal was 160 -190 for me loaded on the highway at 24,000#.

 

[Too Tall]

Sam,

Yes, indeed. Shifting the trans to Neutral when stopped at a light will definitely help to keep the trans cool. In Drive (at a stop) you are generating heat in the converter, due to the speed difference between the engine (idle speed) and trans input (zero speed). If you shift to Neutral, the trans input spins up to almost match the engine RPM, so you have almost no heat generated.

Nice to have an expert on this forum. Can you tell me why the temperature rise so dramatically when towing up a mountain? With the torque converter locked up it would think the temp would stay lower. Is the heat generated from gears being loaded more than usual?

 

[transe]

Nice to have an expert on this forum. Can you tell me why the temperature rise so dramatically when towing up a mountain? With the torque converter locked up it would think the temp would stay lower. Is the heat generated from gears being loaded more than usual?

I presume you're talking about towing at highway speeds, where the Torque Converter Clutch is locked (so you're not generating heat within the converter). Basically, any inefficiency in the transmission gets converted into heat. Let's suppose your trans is 96% efficient under these conditions. In 5th gear, the 68RFE is using two of the planetary gearsets to transmit torque, and you generally loose about 1% per gearset. And let's suppose your pumping losses (to maintain line pressure and cooler flow) are 2%. That's in the right ballpark. So then, 4% of the total power coming from the engine is getting converted into heat inside your transmission. So that is the source of your heat (even if the TCC is locked).

Now when climbing a grade, the power requirements go up significantly. For example, I just looked at a simulation I run for a 2500 truck with trailer. Now the exact figures will vary depending on weight, tire size, axle ratio, frontal area, etc. But (for the particular configuration I was running) I found the propshaft torque required on level ground, at 50 mph, was 211.7 ft-lbs. On a 7% grade (again at 50 mph), the prop torque required was 890.5 ft-lbs. So it takes over 4 times as much power to climb the grade as on level ground. Therefore, you are putting over 4 times the amount of heat into your trans (when climbing a 7% grade) as you would be on level ground. And that is why your sump temp increases.

 

[jacknife]

Good info . Thanks for taking the time to explain it

 

[Apache]

I presume you're talking about towing at highway speeds, where the Torque Converter Clutch is locked (so you're not generating heat within the converter). Basically, any inefficiency in the transmission gets converted into heat. Let's suppose your trans is 96% efficient under these conditions. In 5th gear, the 68RFE is using two of the planetary gearsets to transmit torque, and you generally loose about 1% per gearset. And let's suppose your pumping losses (to maintain line pressure and cooler flow) are 2%. That's in the right ballpark. So then, 4% of the total power coming from the engine is getting converted into heat inside your transmission. So that is the source of your heat (even if the TCC is locked).

Now when climbing a grade, the power requirements go up significantly. For example, I just looked at a simulation I run for a 2500 truck with trailer. Now the exact figures will vary depending on weight, tire size, axle ratio, frontal area, etc. But (for the particular configuration I was running) I found the propshaft torque required on level ground, at 50 mph, was 211.7 ft-lbs. On a 7% grade (again at 50 mph), the prop torque required was 890.5 ft-lbs. So it takes over 4 times as much power to climb the grade as on level ground. Therefore, you are putting over 4 times the amount of heat into your trans (when climbing a 7% grade) as you would be on level ground. And that is why your sump temp increases.

Thanks TransEngineer. Your explanations are always a great source of information.

In 2013, I moved to the Aisin on my RAM 3500 which I work pretty hard off road in 4x4 low. I notice the Aisin runs a little warmer than the 68 rfes' did but it feels stronger even with 3:42 gears. In Arizona summer with outdoor temps running ambient 100+ degrees, I've seen the Aisin as high as 205 degrees pulling livestock off road up 10-15% mountain grades in 4x4 low.

Highway it runs around 160 to 175 degrees in the summer. I'm always watching the temps but so far no ill effects and the Aisin runs strong.

I just ordered a 2015 RAM 3500 Aisin with the 3:42 gears. Would 3:73 gears in 4x4 low run the transmission noticeably cooler?