Towing with Sienna/Rav4/Highlander?

[Mike Magee]

Originally Posted by Glenn Baglo

Can't recall your tow vehicle Mike, but the manual for my RAV4 says to tow in 4, not in Drive and not to tow uphill for any extended time in 3. Toyota wants you to leave in in 4 and let the vehicle do the downshift as required.

Showing off, I dropped down to 3 and headed for the top of the Coquihalla at 60+ mph once ( with the trailer ). Almost got to the top when the transmission overheat light came on. Moved it back to 4 and eased off. All OK in the end, but I won't do it again. ( had a scheduled full service including transmission fluid shortly after ).

I don't recall seeing anything like that in my Highlander's manual. And I really can't imagine why the tranny would get hotter in 4th gear than it would in 3rd. The lower gear is moving fluid through the cooler more quickly, I think, so it should do better. I've had mechanics tell me that it's perfectly ok to run a vehicle all day long in a lower gear at, say, 4000 rpm, and that although it sounds noisier it's really easier on the drive train than using the higher gear.

[Mike Magee]

Originally Posted by Francesca Knowles

Good grief- it's not like you have to confess or anything, Mike. That's a great little trailer and a lot lighter than some of the big boys in this so-called "lightweight trailers" forum!

Sheesh...it's like folks think there's been an "outing" or something...

Stick with us, Mike!

Francesca

P.S. to all:

And can everybody please stop saying "SOB"???

In the first place it's rude, and in the second place it was coined at the Airstream Forums and it's their derogatory term for anyone that "can't" own an AIRSTREAM.

Yes....that's right...fiberglass trailer are "SOB's" by definition, so let's just knock it off with using that term against our own members' rigs.

End of speechifying. For now.

Have a nice day!

F.

Confession is good for the soul. Sorta like an alcoholic at an AA meeting... here I stand, admitting I'm a SOB owner....

And what, pray tell, is wrong with saying "Some Of a Biscuit?" --gotcha--

[Glenn Baglo]

Originally Posted by Mike Magee

I don't recall seeing anything like that in my Highlander's manual. And I really can't imagine why the tranny would get hotter in 4th gear than it would in 3rd.

I didn't say it gets hotter in 4. I said my manual says to use 4 and not to tow uphill in 3 for an extended time. I'll dig out the book and quote the section tomorrow.

[Glenn Baglo]

The manual says: "Do not continue hill climbing or hard towing for a long time in the '3', '2' or 'L' position. This may cause severe automatic transmission damage from overheating. To prevent such damage, the '4' position should be used in hill climbing or hard towing."

This info was under Automatic Transmission, not under the towing section where one would expect to find it.

BTW, the grade on the Coquihalla Highway leading to the summit is generally 6-7 per cent but is 11 per cent on a short section ( which would be about where I got the warning light ).

[Brian B-P]

Originally Posted by Mike Magee

And I really can't imagine why the tranny would get hotter in 4th gear than it would in 3rd. The lower gear is moving fluid through the cooler more quickly, I think, so it should do better.

I assume you meant "I really can't imagine why the tranny would get hotter in 3rd gear than it would in 4th", since that's the situation which Glenn described.

One potential reason is that the torque converter lockup clutch is only functional in some gears - at least the top gear, but probably not all the way down the range; my 5 speed Sienna locks up in at least 5th and 4th. Given a choice of locked up in 4th, or churning the unlocked torque converter in 3rd, 4th would run much cooler. All slippage in the torque converter - which is roughly 10% of the input shaft speed when in coupling mode - multiplied by torque transmitted is power lost. It may be about heat generation (by hydrodynamic losses), rather than heat dissipation (out the cooler).

Originally Posted by Mike Magee

I've had mechanics tell me that it's perfectly ok to run a vehicle all day long in a lower gear at, say, 4000 rpm, and that although it sounds noisier it's really easier on the drive train than using the higher gear.

That is likely true for some specific transmissions (and not the engine), especially old 4-speeds (most are 5 or 6 speeds now, and 8-speeds are becoming common). If you want to know how to fix something, ask a mechanic. If you want to understand vehicle design and operating procedures, there are better sources.

[MC1]

Originally Posted by Francesca Knowles

And can everybody please stop saying "SOB"???

In the first place it's rude,
Have a nice day!

For the record. The term "SOB" was coined as a short form for "some other brand".

For example.... If we sold our Airstream and bought an egg, the egg would be "SOB". If FK sold her egg and bought an Airstream, or Mallard, or Holiday Rambler, she would have "SOB".

There you have the "real story". No big deal.

[Mike Magee]

Wow, hmm, I just always assumed that the TC would be locked up in any gear below the highest gear in which it's locked up. How weird! I wonder why they would engineer a tranny to lock up in 4th, but not in 5th, 3rd, 2nd...?

I just checked my Highlander manual, and it does not contain a similar warning against use of 3, 2, or 1 on grades. Perhaps its tranny is not the same as the Rav4's.

[Carol H]

Originally Posted by Glenn Baglo

BTW, the grade on the Coquihalla Highway leading to the summit is generally 6-7 per cent but is 11 per cent on a short section ( which would be about where I got the warning light ).

Yup the Coq has been known to take a few hostages....hot summer day is when you often see the wounded parked along the sides of the road, its a long long grade climb. I have only pulled across it twice and no warning lights but I now tend to take the slower scenic route when possible.

Its funny to hear that some cant lock on all gears - why is that? I can lock it on 4 & on down with the Subaru.

[Francesca Knowles]

I love my manual tranny...

Francesca

[Glenn Baglo]

Ya, well, when you are showing off, running up the steepest section, from the snowshed to the summit, with a loaded trailer in tow, and doing 60+ miles per hour in 3rd, you get what you deserve.
Done it many times in 4 and only dropped down to 55ish.

[Carol H]

Originally Posted by Glenn Baglo

Ya, well, when you are showing off, running up the steepest section, from the snowshed to the summit, with a loaded trailer in tow, and doing 60+ miles per hour in 3rd, you get what you deserve.
Done it many times in 4 and only dropped down to 55ish.

Yup you see the same thing in the Cascades, I always have a little giggle to myself if I pass someone broken down on the side of the road if they were one of the ones who flew by me earlier on.... I may not win a race but I do get to my destination without a big tow or repair bill

[Brian B-P]

Originally Posted by Mike Magee

Wow, hmm, I just always assumed that the TC would be locked up in any gear below the highest gear in which it's locked up. How weird! I wonder why they would engineer a tranny to lock up in 4th, but not in 5th, 3rd, 2nd...?

I doubt anyone would build an automatic transmission that locked up in 4th, but not 5th - no one has mentioned one in this discussion as far as I see.

Why not the lower gears? Perhaps because conventional automatic transmissions (torque converter, planetary gearsets) are insanely complex, and it may be a mechanical design issue rather than just a control logic matter.
Perhaps it doesn't usually matter because lockup is only important when the torque converter is in coupling mode, which doesn't normally happen for sustained period in the lower gears.

Originally Posted by Carol H

I can lock it on 4 & on down with the Subaru.

Is it only a 4-speed auto?
Are you sure it locks up in first through fourth? I've never seen a torque converter lockup control available to the driver - only overdrive lockouts and tow/haul mode switches; I've never seen an indicator of lockup on an instrument panel. Most people have no idea what gear the transmission is using at any moment - let alone whether it is locked up - and even when I try to follow what is happening myself by watching engine speed it can be hard to tell in anything but a steady-speed situation.

We have one member here who couldn't tell the difference between his transmission shifting between 3rd and 4th (in a four-speed auto) and the torque converter clutch locking up... and I don't really blame him.

[Carol H]

Originally Posted by Brian B-P

Is it only a 4-speed auto?
Are you sure it locks up in first through fourth? <cut>
We have one member here who couldn't tell the difference between his transmission shifting between 3rd and 4th (in a four-speed auto) and the torque converter clutch locking up... and I don't really blame him.

All I can tell you Brian is that when I take it out of automatic and into what Subaru calls "Sport Mode" the indicators on the dash light up and tell me its in Sport Mode and and it only has 4 gears to choose from & what ever gear its in reads out very clearly on the dash. If its in 2nd gear for example there will be indicator reading a big red 2 and the car will red line just like a manual transmission unless I manually shift it out of that gear. Use it all the time. Perhaps I'm mistaken as to what lock out is? Assumed it meant you locked into a gear and it would not automatically shift to another. Either way I shift into Sport Mode when I dont want the car to go into overdrive which it does in Auto mode or to stop it from hunting up and down for gears on a hill.

[Brian B-P]

Originally Posted by Carol H

All I can tell you Brian is that when I take it out of automatic and into what Subaru calls "Sport Mode" the indicators on the dash light up and tell me its in Sport Mode and and it only has 4 gears to choose from & what ever gear its in reads out very clearly on the dash.
...
Perhaps I'm mistaken as to what lock out is? Assumed it meant you locked into a gear and it would not automatically shift to another. Either way I shift into Sport Mode when I dont want the car to go into overdrive which it does in Auto mode or to stop it from hunting up and down for gears on a hill.

Thanks Carol, that answers my question.

The discussion Mike, Glenn,and I were having was about torque converter lockup - a clutch engaging inside the transmission which locks the input side of the torque converter to the output side, eliminating slippage for efficiency and thus reducing heat generation under heavy load such as towing. That's completely unrelated to locking out - or disabling - the higher gears (such as by choosing the lower-numbered positions of a traditional automatic shifter)... which is still not quite the same as manually selecting a specific gear (as you do with the Subaru sport mode)

In short: you don't know if it is lockup up the torque converter, and confusion on the subject of transmission design and operation is understandable.

You may have a 5-speed which offers only 1st through 4th in Sport mode, because you are only expected to use that mode when high power is needed.

[Carol H]

Originally Posted by Brian B-P

You may have a 5-speed which offers only 1st through 4th in Sport mode, because you are only expected to use that mode when high power is needed.

Actually really dont want to or need to know how it all works, just that it does. but I do know I have 5 speed or as I like to call the 5th rightly or wrongly, overdrive, when in auto. Only way I know to stop it from hunting around or going into overdrive, is to put it into 4th manually. Was also told by the dealer it was the best gear for me to use on long climbs etc.... which makes me think it probable does also have torque converter lockup in 4th at least.

[Jared J]

Torque converter lockup can get goofy. The Titan locks in fourth and fifth, BUT&hellip;if its in fifth (overdrive) and downshifts to fourth, it is only partially locked up in fourth. If you manually shift it to fourth, it's fully locked.

This is one of the reasons why it's best to manually downshift, if its going to be in a lower gear for a bit. That also keeps the heat down.

[Mike Magee]

Can we discuss whether there's a way for a layman to know when the torque converter is locked? I've been under the assumption that I could tell by the behavior of engine RPMs, but maybe I'm wrong.

In high gear (5 for my HL), when under some strain the RPMs will climb by about 500. It's not a shift to 4, because a shift would raise RPM about 1000. So I figured this rise in RPM was attributable to slippage in the TC.

Since I have never observed a similar phenomenon when the SelectShift is in 4, 3, or 2 I assumed that the TC was locked up and preventing slippage. Is this an invalid asumption?

[MC1]

Originally Posted by Mike Magee

In high gear (5 for my HL), when under some strain the RPMs will climb by about 500. It's not a shift to 4, because a shift would raise RPM about 1000. So I figured this rise in RPM was attributable to slippage in the TC.

I have seen the same RPM increase (actually about 300 RPM increase) in similar situations. I too believe it to be the electonics knocking it out of TCLU*.

*torque converter loc up.

[Jon Vermilye]

Originally Posted by MC1

I have seen the same RPM increase (actually about 300 RPM increase) in similar situations. I too believe it to be the electonics knocking it out of TCLU*.

*torque converter loc up.

That is the way I've always identified the TC unlocking. I do wish there was a manual lock available, but I suspect it would cause more problems than it would solve for non - towers...

[Thomas G.]

Maybe something like a scan gauge can be set to identify this.

Years ago I used to tune the internal dampers in torque converters and I had the transmission engineers build a box that identified what gear it was in, whether the converter was locked and also has a manual locking switch. It helped a lot as it is difficult to tell just from cues from the tachometer.