Towing- benefit of selecting "no OD" on transmission?

Towing season is coming soon and I will use the button to turn off the overdrive on my transmission ('01 Toyota Sequoia, V8, 4WD, Auto) as recommended by the owners manual and posters on this board.

My question is when you turn off the overdrive and the dashlight is illuminated am I in 4th with the lock up torque converter turned off? Or, am I in 3rd with the lock up torque converter “on” (or locked).

What are the benefits of turning the OD off? Am I reducing wear on the transmission? Am I gaining more engine braking? If going downhill does it make sense to turn the OD back on as long as speed does not build up?

I have 2 trailers. One is a boat trailer with surge brakes weighing about 4,000 lbs. The other is a bumper pull 2 horse trailer with electric brakes that runs about 5,000 lbs loaded with the horses. I will use interstates, some hills, and figure to stay around 60 mph when towing.

I do what the manual says…I tow heavy loads as well and lock out OD with my Toyota as the manual says “all of the time”. To me it’s a no brainer.
I don’t believe that size motor IS over reving at any speed under 60 mpg w/o OD. I don’t over think or negate the engineer’s intent.

I leave myself open to correction - but my understanding is that with OD turned off you have all 4 gears but no TC lockup.

I’m sure that there are a number of reasons that you should turn it off to tow - but basically the root of it will be the frequent need of extra torque. With the TC locked up you have less torque - the trans will need to kick it on & off a lot. This will produce extra heat and wear, and you’re already making enough of that by towing.

It may depend on brand, on my Suburban OD off meant 3 speeds instead of 4. Intended to keep engine from lugging and overheating is my understanding.

Thanks to all who gave an opinion.

I carefully read the owner’s manual again. Pushing the O/D button “off” puts the Sequoia in 3rd, no mention of whether or not the lock up torque converter is locked or not. Only reason given for towing in “D” without overdrive on is “In order to maintain engine braking efficiency, do not use overdrive.”

My 04 4Runner may or may not lock in 3rd but all my gears provide significant braking when not in OD. I don’t think Toyota changes basic function from one model to another much.

Overdrive relates to the gear(s) with better than a 1:1 ratio. I.e. .96 to 1. Its more efficient when cruising, but has little “oomph” due to the super low ratio. Turning off OD disables the gear(s) that are smaller than 1:1.

RE: Dagosa "I don’t believe that size motor IS over reving at any speed under 60 mpg w/o OD."
What does size of engine have to do with over-revving? The bigger an engine the MORE likely it is to over-rev. Big engines tend to make power at lower bands.

I had a 5.4 v8 F250 Automatic that would shift (“hunt”) between 3 and 4 if left in Auto Overdrive. Lugging engine followed by long slipping shifts from 4th to 3rd while going up hills and back to 4th down hill. I believe this is hard on the tranny and why its often recommended by the manufacturer. The 5.8’s owners manual recommended switching off Overdrive in that situation. My V10 F250 does not know the load is back there. I just mash the pedal:)

The OD gear is small and somewhat fragile. The only people who know what the torque converter is doing are Toyota transmission engineers or other transmission experts. I SUSPECT the torque converter locks up and stays locked up in both direct and overdrive, whichever gears they may be…Overdrive can make the transmission hunt and downshift unnecessarily when pulling heavy loads. Lock it out.

Indeed - thanks for clearing that up as I now do understand it. Oddly enough I was given this impression about the TCC by a Ford mechanic once re: my own car - long story.

But it leaves me to wonder why the designation “overdrive” only seems to be associated with automatics. Obviously in a manual there isn’t an “OD-off” since the driver does the shifting, but wouldn’t many manuals’ top gear be an “overdrive” gear? Or are many manuals actually called an X-speed with overdrive (meaning X + 1)? I’ve only heard the reference re: automatics, and it is only those for which a TCC applies.

I have seen fifth gear marked “O” on the shift pattern of some manual transmission pickups but usually it is simply marked “5” even if it is in fact an overdrive.

The term “overdrive” originally was used for an auxillary two speed gearbox that was in tandam with the normal 3 speed transmissions commonly used in cars back in the days of six volt car batteries, generators, and horsehair and oil air filters.

With overdrive "off’ you will run no higher than 3rd gear. The converter should lock up in 3rd. 4th or "overdrive’ puts a strain on things when pulling a trailer and it will keep shifting up and down.

Overdrive “off” will keep the tranny from shifting to 4th and the converter will lock up in 3rd.

Thanks, UT