Trying to figure out what's normal towing temps/operation

[HookMeUp]

This weekend was the second time towing with our 2011 3500. Running the hills in eastern Iowa @ 65mph, it will not hold in 6th OD, keeps down shifting to 5th with trans temps running 168-170 and engine temp 195. So I have been running with the ERS set on 5th, which eliminates downshifts, trans temps running 158-160 and engine temps 200, reaching 210 at the crest of the hill. So is this normal and is it ok to run with 6th locked out?

 

[mpaulson]

You're temps all look totally normal to me, about the same thing on my last trip two weeks ago with the full load. I run locked in fifth as well when there are constant rolling hills while loaded and then use 6th gear once things flatten out. You don't have your gear ratio in your signature but you will be fine since I have 4.10's and that works out fine in 5th for me at 110 kmh(68 mph), 2300 rpm pulls like a freight train and doesn't slow down on any of the mountains that I've hit yet and any ratio below that would be even better and lower rpm in fifth.

 

[sag2]

Just pulled this weekend with 14 3500. At less than 60 it would not shift into 6th. Had to be at least 62 and then would go into 6th but downshifted into 5th all the time unless I held it in 5th. Temps were about the same as yours. Ambient was 75-90 and altitude sea level to 7500 feet. Didn't really matter on altitude, still felt the same.

 

[Cummins12V98]

All sounds normal.

 

[HookMeUp]

Just updated signature, running 3.73. Thanks for the replies, I had a 2002 with 6-spd manual before getting this. I've never towed with an automatic, I've always had manuals. With the 2002 the fan would kick in when temp went over 200, on the 2011 at 210 I still didn't hear the fan kick in, but once at the top it would immediately drop down in temp. These newer ones must run a little hotter.

 

[gtoli]

The fan on my 2010 can be heard coming on at "low" speed at 215* and high speed at 218*. Was towing my 7k lb. travel trailer through Kingman, AZ at 100* outside temp and saw up to 220* coolant and 187* trans. The coolant temp would drop back down to 210* quickly when the fan came on.

 

[Bill Stockard]

Just pulled this weekend with 14 3500. At less than 60 it would not shift into 6th. Had to be at least 62 and then would go into 6th but downshifted into 5th all the time unless I held it in 5th. Temps were about the same as yours. Ambient was 75-90 and altitude sea level to 7500 feet. Didn't really matter on altitude, still felt the same.

Were you driving a 3500 SRW with a 3.42 ratio?

Bill

 

[RustyJC]

My 2011 towing the RV in my signature will run coolant temps of 201-203 degF and transmission temps of ~172 degF on the flats with cruise control set at 65 MPH and running in 6th gear. Even with 4.10s, long grades will drop it back into 5th gear. That's a function of the double overdrives in the 68RFE (as compared to the single overdrive 6th gear in my previous 2002 with the NV5600) - 65 MPH in 6th in the current truck is only about 1750 RPM versus 2200 RPM in the 2002, so a downshift to 5th when speed drops to around 60 MPH kicks RPMs up to 2100 or so where the Cummins has no problem pulling the speed right back to 65 MPH.

On extremely long grades in higher ambient temperatures, I've seen engine temps go as high as 219 degF where the engine fan kicks into Warp 9 mode and temps drop back very quickly. Trans temps can go up to and slightly over 200 degF in sustained low speed 1st/2nd gear work where the torque converter isn't locked up and there's not much airflow through the cooling pack. The highest trans temp I've ever seen is 215 degF dragging our previous 5th wheel up the side of a mountain in Arkansas on a hot day on a road with lots of switchbacks that kept us in 1st and 2nd gears for the entire pull.

Rusty

 

[HookMeUp]

All good information.

Rusty, mine has the 3.73 so at 65mph its turning 1600RPM in 6th and 2100RPM in 5th. My old 2002 with 6spd, was 1850RPM in 6th running 65MPH and I didn't have to shift out of overdrive over the same stretch of road. I just wonder if the 800 lb.-ft. torque would hold overdrive?

 

[RustyJC]

All good information.

Rusty, mine has the 3.73 so at 65mph its turning 1600RPM in 6th and 2100RPM in 5th. My old 2002 with 6spd, was 1850RPM in 6th running 65MPH and I didn't have to shift out of overdrive over the same stretch of road. I just wonder if the 800 lb.-ft. torque would hold overdrive?

Perhaps, since the 800 doesn't have the 650 lb-ft engine's computer-managed flat torque "curve" (although I don't recall the torque curve of the 800 being that much higher than the 650 down at 1600-1700 RPM), but it all depends on how the Ram engineers have the thing programmed. Perhaps because of torque limiting (torque converter lockup clutch capacity - the torque converter was upgraded on the 800), high egts at these lower engine speeds, emissions considerations, etc., they want the engine to downshift and rev when under load. I really don't have enough information to speculate on why the 5th gear downshift is programmed the way that it is. My rationale is that the engineers did a LOT of testing to determine their computer algorithms, so I just drive the bloody thing and let the computers take care of protecting the drivetrain.

Rusty