5th gear towing?
- Thread starter Fred MaN
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Fred MaN said:
I guess whether to be in 4th or 5th gear depends on the load you're pulling and terrain you're covering. Your 4Runner can run all day at 3100 rpm with no problem. I much rather be in a lower gear (higher numerical gear ratio) running at a higher rpm than in higher gear (lower numerical gear ratio) running at a lower rpm and "lug" the engine.
Fred MaN said:
This is Toyota Motor's advice, not just the dealer's. Two reasons for this:
-In fifth gear (OD), the torque converter is much more likely to unlock and run for long periods unlocked. This generates heat, which is bad for the life of tranny components. It also costs fuel economy, as the unlocked torque converter is churning away and generating heat which you have to burn fuel to produce.
-Towing in 4th (or with OD locked out in older 4- speed A/T 'Runners) gives you much better engine braking, aways a nice thing to have when towing.
I tow a 4,000# trailer, and did with my previous '98 'Runner as well. It's easy to learn to recognize when your torque converter unlocks: There's a jump in rpms that's less than occurs if you downshift to 4th. It's about 200 rpms for our '03 V8, and was ~ 400 rpms for our '98. If this happens and doesn't drop back into lock within 60 seconds or so, it's time to manually downshift to 4th. This will let the converter lock itself and begin to cool back down.
If you're diligent about watching for this and are in a situation where you don't need engine braking, running in OD/5th shouldn't hurt anything. I have to admit that monitoring this is something of a PITA. I think it does pay off, though: Our '98's tranny still worked like new at 75K miles and 30K tow miles when I traded it in.
BTW, I agree that 3100 rpms won't hurt a Toyota engine - our '98 ran at 4800 or more for many minutes climbing Interstate grades in 2nd gear in the mountains of V VA.
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TechWrench
Senior Member
Re: Re: 5th gear towing?
The heat generated by the torque converter at crusing speed is not all that much. The torque converter generates heat because of the 'shearing' action in the fluid, and this shearing increases as the load (and need for torque multiplication) increases which happens at start-up from a stop, and heavy pulling. The lock-up function in the torque converter is accomplished by a friction clutch which is not able to sustain heavy torque loads, that is why is automatically disengages under heavy load or acceleration/deceleration.
I do agree that towing in 5th should not be a problem, as long as you are on a level grade, and the engine isn't lugging. The control ECU for the trans is programed to compensate for most driving conditions. It will usually do a good job of selecting the proper gear for load and speed condtions. If the trans is constantly 'hunting' between OD and the next lower gear, then it is time to manually downshift to force the lower gear until conditions allow OD to be sustained again. The reason the trans downshifts under load is to allow the engine to operate in its optimum power band range, more than trying to save heat generation.
khaug said:
The heat generated by the torque converter at crusing speed is not all that much. The torque converter generates heat because of the 'shearing' action in the fluid, and this shearing increases as the load (and need for torque multiplication) increases which happens at start-up from a stop, and heavy pulling. The lock-up function in the torque converter is accomplished by a friction clutch which is not able to sustain heavy torque loads, that is why is automatically disengages under heavy load or acceleration/deceleration.
I do agree that towing in 5th should not be a problem, as long as you are on a level grade, and the engine isn't lugging. The control ECU for the trans is programed to compensate for most driving conditions. It will usually do a good job of selecting the proper gear for load and speed condtions. If the trans is constantly 'hunting' between OD and the next lower gear, then it is time to manually downshift to force the lower gear until conditions allow OD to be sustained again. The reason the trans downshifts under load is to allow the engine to operate in its optimum power band range, more than trying to save heat generation.
khaug said:
Khaug is 100% right. You shift up to 5th/Overdrive and keep your eye on the RPMs, if you don't *SEE* the 200 RPM drop off within a few seconds then it's not locking up, and you SHOULDN'T leave it there.
This may surprise you: The gas mileage in 4th, with the Tranny locked, is typically very close to the gas mileage in 5th when 5th is unlocked and wasting torque as "sloshing around", heating the Tranny fluid.
Just change your oil and diff fluid often, lube the propeller shaft points often, and then just BE HAPPY in 4th if your 4R refuses to lock in 5th.
BTW, I've got a very light RV (only about 4K loaded). I tow in 5th a lot... but I pay attention and downshift BY HAND to 4th, 3rd, or even 2nd as conditions demand. The auto isn't quite smart enough to handle towing by itself.
But if you want to set your lever in one place and forget it, then leave it in 4th, as Toyota says. You usually need to PAY ATTENTION in order to tow much of any load in 5th.
TechWrench
Senior Member
Re: Re: 5th gear towing?
With the way the lock-up function works in the torque converter, just downshifting to 4th (or 3rd) in the 4speed auto, does not automatically insure the converter will lock-up or stay locked-up. As I stated earlier, the lock-up function is designed to hold under very limited load conditions. If the ECU senses load conditions outside its 'comfort' range, it will not engage lock-up in the converter. The lack of converter lock-up does not mean you are going to damage the trans. All you are loosing is a little efficiency, and generating a little more heat which the trans is capable of dealing with. The main reason for downshifting under load is to keep the engine in its power band 'sweet' spot.
rickst29 said:
With the way the lock-up function works in the torque converter, just downshifting to 4th (or 3rd) in the 4speed auto, does not automatically insure the converter will lock-up or stay locked-up. As I stated earlier, the lock-up function is designed to hold under very limited load conditions. If the ECU senses load conditions outside its 'comfort' range, it will not engage lock-up in the converter. The lack of converter lock-up does not mean you are going to damage the trans. All you are loosing is a little efficiency, and generating a little more heat which the trans is capable of dealing with. The main reason for downshifting under load is to keep the engine in its power band 'sweet' spot.
