Overdrive while towing?

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Patrik

10 Year 15 Year
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Aug 11, 2009
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I have a 2000 LC with 140k miles. I am going to use it to tow my new boat. The boat+trailer probably come in at about 2500-2800 Lbs. Should I turn the overdrive off while I am towing? If so, should I turn it off no matter the speed or just turn it off when hitting 50 MPH or more?

Thanks!
 
When we tow our boat, i turn overdrive on/off based on the terrain more than speed. Usually I would leave it off unless im on the highway.......if its a relatively flat highway with low traffic levels Ill turn it on.....otherwise i keep it off even on the highway. Main thing to consider is how much speeding/slowing down you have to do in the 30-60mph range.

One more thing, I tow a boat/trailer that weighs in a little over 5000lbs, so maybe someone else would have more useful info, since your towing about half as much weight.
 
my car/trailer is around that if not a little more...i just put it in pwr mode. :D
-75mph no problem....gas mileage.....sucks anyway:D



-just plan your stops a little better.
 
My boat is light (1600lbs) so I usually have it On on the highway or freeway. When I'm in town I keep it off because it helps me stop faster in case of an emergency and it seems to be in a better rpm range for torque and getting it off the line. I towed my buddies boat which is 4000 pounds and all I can say is ouch! I would never buy a boat that big to tow unless I had a diesel motor and 500+ torque. If the tranny starts jumping around gear hunting I usually slow down to around 60mph or less and just turn off the overdrive. I always try to baby my landcruiser in towing situations. Anybody can throw a huge boat behind them and rip down the freeway, but will it stop in an emergency situation that's the question? Also, I've read that towing above 55mph sucks fuel. They've done studies in California where they say that you get 10% better mileage by towing at 55mph than 65mph. I hardly ever tow above 65mph, not that I couldn't it's just that I'd rather save gas, relax, and not have to worry about blowing a trailer tire as I'm always worried about that.
 
in mountains or when towing...I turn off OD and also turn on PWR mode....the two seem to help it quit hunting for gears especially if on cruise control. Will also keep your tranny from overheating and cause your torque converter to lock up better....both good for your rig.
 
I would turn it off during any around town stop-and-go traffic and leave it on when cruising the highway. If you pay attention to the tachometer you should be able to tell when the transmission is happy (staying in one gear) or not (hunting for gears).

If you want more info, this is about the A343F transmission in the 80 series, but I think it applies just as well to the pre-03 100 series trucks.
96r50 said:
The A343F is a 4 speed automatic with overdrive (O/D). What this means is that there are 4 gear ratios, and the last one (4th) is overdriven (the output shaft spins faster than the input shaft). 3rd gear is "direct drive" since it is a 1:1 ratio (input and output shaft speed is the same), while 1st and 2nd are underdrive (output shaft spins slower than the input shaft). The transmission also has a locking torque convertor which allows it to minimize the power loss that is present in automatic transmissions due to the fluid coupling. The torque convertor can only lockup in 4th gear (a.k.a. overdrive).

On the centre console your shifter has three forwards-drive positions: 1, 2, and D (3rd). You also have the O/D switch on the shifter handle, which is essentially just saving you from having a fourth shifter position. With the shifter in D and the O/D switch on (pushed in, no light on the dash) the transmission has free range of all 4 gears, and can lock the torque convertor when in 4th (O/D). With the O/D switch off (popped out, light on the dash) the transmission can only use gears 1,2, and D (3), and the torque convertor will not lock. With the shifter in 2nd, it is limited to 1st and 2nd, and with the shifter in 1st, it is limited to first gear only.

Gear Ratios (found online)
1st: 2.804:1
2nd: 1.531:1
3rd: 1:1
4th (O/D): 0.753:1

Hope that helps!
Click to expand...

So if you turn off the O/D, you've lost 4th gear and the ability for the torque convertor to lock up. When towing, I usually leave O/D on until I notice the transmission shifting up and down to maintain headway.


Brock said:
in mountains or when towing...I turn off OD and also turn on PWR mode....the two seem to help it quit hunting for gears especially if on cruise control. Will also keep your tranny from overheating and cause your torque converter to lock up better....both good for your rig.
Click to expand...

O/D off will not keep the transmission from overheating, and the torque convertor will not lock up at all.
 
IDK for sure, but I think some of that changed for the 100. Mainly the gears that it can lock up in.......but im still uncertain as too which of the 4 it can lock up in. I know for sure it can in 4th, I think it does in 3rd as well. I know this seems crazy, but I almost want to say that someone said it can lock up in 1st and 2nd......which seems wrong......maybe that was the A750?......does anyone know for sure?
 
The best way to determine if you should turn O/D off is to watch your Tach. When you are cruising in 5th gear (or 4th pre-2003) and there is little strain on the drivetrain you will notice the RPM drop by about 100-200 - that is when the torque converter locks up and your tranny is happily cruising. You will also notice that your drivetrain quiets down a bit.

If you notice that the torque converter never locks (too much weight, headwind or climbing a hill) you should consider shifting into 4th (or 3rd) or turning OD off. Around town, OD off probably makes no difference.

You can get a good feel of the torque converter lock point by driving on the highway without your boat. Accelerate to 65 or 70 and start cruising. If all is well you should see that tell-tale RPM drop on the tach when it locks.
 
When towing I have used OD most of the time. When the tranny starts dropping out of OD frequently because of a variety of reasons (terrain, wind, weather), I take it out of OD. I also use the Power mode, and use 91-93 octane fuel. On flat terrain and about 60-70 mph, the OD has worked fine in most conditions. I also use synthetic fluids throughout.
 
96r50 said:
O/D off will not keep the transmission from overheating, and the torque convertor will not lock up at all.
Click to expand...

This is definitely not how my trans acts when I switch OD off. I don't have any experience with the 80, but on my 98 when I switch OD off, the transmission highest gear is 3rd AND the TC will stay locked up in 3rd for the majority of driving conditions.

When towing, my decision for when to turn off OD is based upon the driving conditions and what the TC is doing. Basically trying to eliminate as much heat from the system as possibly.

Rich
 
pman said:
IDK for sure, but I think some of that changed for the 100. Mainly the gears that it can lock up in.......but im still uncertain as too which of the 4 it can lock up in. I know for sure it can in 4th, I think it does in 3rd as well. I know this seems crazy, but I almost want to say that someone said it can lock up in 1st and 2nd......which seems wrong......maybe that was the A750?......does anyone know for sure?
Click to expand...

richg said:
This is definitely not how my trans acts when I switch OD off. I don't have any experience with the 80, but on my 98 when I switch OD off, the transmission highest gear is 3rd AND the TC will stay locked up in 3rd for the majority of driving conditions.
Click to expand...

If it can lock up in third gear that's a nice feature. When you watch the tach with O/D off can you see the slight drop (rpm) when the TC locks up in third gear?
 
96r50 said:
If it can lock up in third gear that's a nice feature. When you watch the tach with O/D off can you see the slight drop (rpm) when the TC locks up in third gear?
Click to expand...

Yes, you can see the RPM drop as the TC locks up in 3rd, and you can watch how the RPM tracks with speed more like an MT car when it is locked up.

Rich
 
I have left mine on when towing a ski boat. Then again, I also did not drive over 65 MPH
 
Had overheating issues when climbing inclines on and off road at any speed and thanks To all of the information on these threads I have taken the advised steps of replacing the radiator, hoses, thermostat and fluids. Will reply I'n a few days with the results total cost as yet $700. A small investment for trouble free motoring.
Cheers
 
I tow a lot. I have an 01 LX with the 4 speed. I prefer the regular mode instead of the power mode for the transmission as it seems to hold a gear longer before downshifting in light throttle situations. When the OD is switched off, the torque converter can then lock in 3rd gear, which is nice when climbing a serious grade at highway speeds. If you like, pay attention the next time you are empty going up a steep grade and the truck downshifts to 3rd gear. The torque converter will be unlocked. press the OD off switch. The torque converter will lock. You can see this by watching the tachometer.

When towing you want things to be as smooth as possible, and if you are in a situation where the transmission is shifting back and forth, locking and unlocking the torque converter, you are putting more wear on things.

I normally tow in regular D with the OD on. I will switch the OD off to assist in braking. I will switch the OD off when climbing a significant grade.

Wind is a difficult situation that I frequently encounter. Sometimes it makes sense to just open the throttle and burn a lot of fuel, but I have also slowed considerably -90km/h or 55 mph and shut the OD off.
 
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