Question about towing in OD

I understand it's bad for the transmission to tow in overdrive. The reasoning I've read pertains to the tranny heating up from frequent gear hunting. So my question is, if your drive is flat and it's not continuously shifting, is it ok to leave it in OD?

The last time I towed my popup (bout 2500lbs), keeping it in 4th had the RPMs were around 4k and the tranny temps around 180. Since it was flat, I shifted into OD which immediately dropped the RPMs and also the tranny temps. If it started to gear hunt I was going to drop back to 4th but it never did. Still bad?

 

Did you regear your truck to a lower set of gears? Mine does not run near 4K rpms in 4th gear but then I run it at 60MPH

 

No regear. It's been a while now, so I don't recall if they were really that high or not. I was driving probably 70mph

 

Thats fine imo, I've done the same. Since having overdrive off causes rpms to be a bit higher, but if I was on flat ground and no gear hunting I would put it into normal mode (on 2nd gens just shift back over to drive) and let the rpms drop.

Did the same on my old half ton towing 6500 lbs plus, never an issue. Usually would just turn overdrive off when I was about to climb a large grade or in an area with a lot of up and down hills.

 

^ That's my mode of operation as well. I was just curious if there were any reasons beyond the gear hunting that I should keep it out of OD. Good to hear I'm not alone anyway.

 

I have thinking the same thing, mine never 'hunted' at all then I was told to drive in 4th. I will be testing all that with the new scan gauge in a couple weeks.

 

You should not tow in od. It's something to do with the tq converter heating up in OD do to design. Tran runs cooler with OD off regardless of it's downshifting or not. If the user manual recommends it to be off I would not tow in OD.

 

My OBD scanner disagrees with you. That's the entire reason for this post and why I'm questioning it. When I put it back into OD, not only did the RPM's drop, but also the tranny temps.

 

That's good then. Could be design of the trans. What's owners manual suggest.

 

I don't see anything in the manual regarding towing in OD. I do see that it says not to exceed 65mph. Oops.

 

When we head out camping it is a 150 mile flat drive - sea level to 1000 feet, when I hit the Sierra's then I know/knew drop it down. I am towing a light trailer - 1100 pounds max and 500 to 600 in the truck bed and that makes a lot of difference.

 

The owner's manual does not say you can't tow in overdrive. It does say you may tow in s4. I'm pretty sure it will help with downhill speed and with excessive gear hunting. I live in the flatlands of Chicagoland tow with the overdrive on.

 

Yeah, seems strange. My '13 runs about 2900rpms at 70mph in 4th. I keep in in 4th while I'm towing no matter what, even when I'm in the north country doing 80.

 

I finally got mine to heat up...
freeway, 60mph, outside temp 75, in 4th for 30 minutes
161 out of converter, 154 in the pan, water temp still 186

Not towing but found my cap weighs 230 pounds

 

Need to watch if the Torque Converter Lockup Clutch is staying engaged. Same to worse for heat buildup as shifting gears.

More engine speed equals more transmission pump speed for flow and possibly pressure. That's part of what hurts diesel automatics is they can lug along in OD at sub2k rpm and pull the load, but the trans pump isn't moving enough fluid for effective cooling and reliable clutch/band operation.

 

Forgive my ignorance, but you lost me at the bolded part.

Are you saying there's more than just watching the pan and torque converter temps? Or are you just pointing out another cause of increased transmission temps?

 

It is another cause of increased temps.

Under cruise conditions, the lockup Clutch is engaged inside the torque Converter. When load is increased (uphill, headwind, accelerate), the clutch will be disengaged and the torque converter will become active again to increase torque input. This will be a small increase in engine rpm and often followed by a downshift which is a larger rpm jump.

I don't know if your monitor has access to TCC Solenoid status (Torque Converter Clutch) to directly monitor versus paying attention to engine rpm. If it is fluctuating (about half the jump of a downshift), then temps are likely to climb and the trans should be downshifted to put less load on the engine/torque converter/transmission.

This is true in 5th and 4th and possibly 3rd

 

I have a Kiwi3 and use the OBD Fusion app. I can monitor transmission temps, but I'm not sure about the TCC Solenoid status.