Towing an M3 with my LX470 (1 Viewer)

[Eliot]

I was driving on all flat ground. Stayed at about 60-65 mph. Tranny never really downshifted at all so almost all the driving was in OD right around 2000 rpms on the engine.

Got 13.5 mpg towing 5400 pounds. 34 psi on stock 31" tires.

I have an appointment tomorrow to get all the ATF exchanged. Will take a sample of the fluid and have Blackstone do an analysis. I'll report the results when I get them back.

 

[gatormark91]

I appreciate all the advice and suggestions. Unfortunately I didn't see the "DO NOT USE OVERDRIVE" because I towed the vehicle on Friday.

So yea I used Overdrive the whole way. Cooling system is brand new. Never had an issue, until I got home.

M3 was undriveable so I had to tug it off the trailer. I did this as soon as I got home after towing 5400 pounds for 5 hours. Transmission was definitely still hot. So the old lady jumped in the Lexus and we used a tow strap to pull the M3 off. Car came off, no issues. I jump back into the Lexus to turn it around and hook it back up to the trailer and as soon as I put it into reverse to back to the trailer, my A/T oil light came on, Check engine light came on, power steering went out, and my engine oil pressure dropped....weird. Shut the Lexus off for a few minutes and then turned it back on...everythings good, no dash lights, power steering works, everythings fine. Backed the remaining 2 foot and hooked the trailer up, then shut the Lexus off.

I let the Lexus cool off for 5 hours and then fired it back up to get the uhaul back. No issues towing the 2200 pound trailer back and Lexus ran fine.

ATF looks clean and has no burning smell to it. At this point I'm thinking my only course of action is to get a fluid exchange on all 15 quarts and then just ride it out...

What do you guys think?

Was the engine running OK when this happened, or did it sound like it was bogging down? Maybe the torque converter lock-up was stuck or something? Weird...

 

[mgoblue]

BMW ownership is the best...driving my S54 swapped wagon home to Virginia the day I bought it...yup, ended up on a flatbed.

 

[uHu]

Re Lock Up vs OD:
The 4-sp box will Lock Up in 4th gear only, when OD is on; and LU in 3rd only if OD is off. So, for towing heavy, you will often be in 4th without LU if you don't turn the OD off (and that's what generates the most heat).
The 5-sp box will LU in 5th or 4th gear, whatever the setting of OD (stick in D or 4). But the LU in 4th comes on earlier if the OD is off.
This is how it is on the HDJ version -- is the UZJ the same?

 

[gatormark91]

deleted

 

[Eliot]

Was the engine running OK when this happened, or did it sound like it was bogging down? Maybe the torque converter lock-up was stuck or something? Weird...

Engine definitely seemed to bog down. I assume that's why the power steering died out and the oil pressure dropped. I turned it off quickly so I could allow everything to cool. Turn it back on after a minute to read codes and everything was fine.

Re Lock Up vs OD:
The 4-sp box will Lock Up in 4th gear only, when OD is on; and LU in 3rd only if OD is off. So, for towing heavy, you will often be in 4th without LU if you don't turn the OD off (and that's what generates the most heat).
The 5-sp box will LU in 5th or 4th gear, whatever the setting of OD (stick in D or 4). But the LU in 4th comes on earlier if the OD is off.
This is how it is on the HDJ version -- is the UZJ the same?

Can you explain what you mean by locking up? Why wouldn't it lock up in 4th gear when towing?

 

[cwmoser]

This "lock up" concept is confusing.
I've read that if your Transmission is not downshifting (hunting a gear) then you are OK to
tow in Overdrive. When the transmission shifts it creates friction which causes heat.
So if your Transmission is not continually shifting gears you can run in Overdrive.
In addition, our LX/LC's have Transmission Coolers to keep the heat down.
My 2002 towing 3500 lbs on flat ground - the transmission does not continually shift gears.
I am betting this is right advice - otherwise the savings I get in Gasoline is much less
than a Transmission rebuild.

 

[flintknapper]

I appreciate all the advice and suggestions. Unfortunately I didn't see the "DO NOT USE OVERDRIVE" because I towed the vehicle on Friday.

So yea I used Overdrive the whole way. Cooling system is brand new. Never had an issue, until I got home.

M3 was undriveable so I had to tug it off the trailer. I did this as soon as I got home after towing 5400 pounds for 5 hours. Transmission was definitely still hot. So the old lady jumped in the Lexus and we used a tow strap to pull the M3 off. Car came off, no issues. I jump back into the Lexus to turn it around and hook it back up to the trailer and as soon as I put it into reverse to back to the trailer, my A/T oil light came on, Check engine light came on, power steering went out, and my engine oil pressure dropped....weird. Shut the Lexus off for a few minutes and then turned it back on...everythings good, no dash lights, power steering works, everythings fine. Backed the remaining 2 foot and hooked the trailer up, then shut the Lexus off.

I let the Lexus cool off for 5 hours and then fired it back up to get the uhaul back. No issues towing the 2200 pound trailer back and Lexus ran fine.

ATF looks clean and has no burning smell to it. At this point I'm thinking my only course of action is to get a fluid exchange on all 15 quarts and then just ride it out...

What do you guys think?

I think you didn't have high tranny temps to begin with. With check engine light on, loss of P/S and sudden low oil pressure, you had some other electrical glitch (poor ground) going on.

You can have your fluid exchanged if you like, but if...as you say the current fluid looks good...it will be a wasted effort.

You didn't hurt your transmission and the sky is not falling despite irresponsible claims to the contrary:

Gator wrote: "You want to kill a trans with high temps tow with OD on."

As previously stated, if your transmission is not hunting between gears and you don't feel as if you are lugging your engine, then you are fine. It is up to the driver to determine when to drop out of overdrive (for sake of staying in the best power-band) and when you can take advantage of OD/TC lock up. Simple as that. There are applications for both.

Read up on the subject and decide for yourself. Don't take my word for it, or anyone else's. It's YOUR vehicle, YOUR driving practices and YOUR responsibility to know the design limits of your rig.

 

[flintknapper]

This "lock up" concept is confusing.
I've read that if your Transmission is not downshifting (hunting a gear) then you are OK to
tow in Overdrive. When the transmission shifts it creates friction which causes heat.
So if your Transmission is not continually shifting gears you can run in Overdrive.
In addition, our LX/LC's have Transmission Coolers to keep the heat down.
My 2002 towing 3500 lbs on flat ground - the transmission does not continually shift gears.
I am betting this is right advice - otherwise the savings I get in Gasoline is much less
than a Transmission rebuild.

^^^^^^^^^^ NO you can't. 'Gator' said so.

 

[jdcascio1]

I towed an S2000 and spare motor with my 98 LX470 (155k miles at the time) from Raleigh/Durham area of NC to Mooresville, NC area no problem. This was during rush hour stop and go traffic on I-77 as well. It was all relatively flat topography, with a few slight hills here and there but nothing major. I did get pretty horrid gas mileage though, but that was to be expected.

 

[gatormark91]

I won't run my trans at 210-220 degrees all day. Nope. Not when I can run it at 150. It is easier for me to put in gas than a replacement trans. Just my irresponsible $.02.

 

[gatormark91]

Here is the clearest explanation I could find on the nets... Not that it is hard to find answers, since almost every search result you find on Google for "Towing with overdrive on or off" says OFF:

quote:
"Overdrive is just that... here's how it works: it makes the wheels turn more than one rotation for every rotation of the transmission/ engine. So basically when you're in overdrive your wheels are spinning faster than your engine, which takes stress off the engine in normal freeway driving when the accelerated mass of your car can maintain your speed and your engine doesn't need to work as hard. But if you are towing more weight, going uphill, etc., it actually makes your engine work HARDER because it has to catch up to the wheels to push that load. It's like this: imagine (and these are just arbitrary numbers) for every 1 rotation of your engine, your wheels are spinning twice. In normal freeway driving, the mass of your car at speed helps to push itself and the engine really only needs that single rotation to every double rotation of the wheels to maintain speed. But if you add weight, you are asking your vehicle to pull up to twice its mass at half engine power. This will make your vehicle sluggish and tear up your transmission, because it's trying to convert the engine's power to wheel power at a lower rate. Your engine will bog down and have to work twice as hard to maintain the same rate of speed.

When you turn overdrive off, it sounds/ looks like your engine is working "harder" but it's really just working normally. Towing is hard on your vehicle anyway, but you are NOT doing it any favors by keeping it in overdrive, you are actually damaging more than you are helping."

 

[chrisratz]

I'm loving these pics of cruisers and bimmers. Cruiser + M car = ideal garage in my opinion.

 

[flintknapper]

I won't run my trans at 210-220 degrees all day. Nope. Not when I can run it at 150. It is easier for me to put in gas than a replacement trans. Just my irresponsible $.02.

No one is suggesting you run your vehicle at a higher trans temp than necessary. Quite the contrary. And in every post I have made....I have allowed that conditions/circumstance must be considered by the driver.

Driving to suit YOUR needs is not 'irresponsible'.

What IS 'irresponsible' is making 'blanket statements' such as:

Gator Wrote:

"DO NOT USE OVERDRIVE. Your trans temps will go way too high. This is absolutely a must-do thing.

You want to kill a trans with high temps tow with OD on."

It is simply untrue in the MANY circumstances you have not allowed for .

In the case you cite....where you were pulling a travel trailer, in certain terrains and conditions...what you did (OD/TC lock out off) might be just the ticket. You were pulling a heavy 'high profile' RV. You were not only pulling 'weight' but also battling wind resistance. With some travel trailers, you might as well be pulling a parachute.

Conversely, the guy that hooks up his bass boat that is less weight and rides in the slip stream of the vehicle will likely never need to get out of OD. Yet your warning (if not rigidly followed) assures those hapless dissenters a failed transmission!

Come on!

Again....(for its worth): There are times when the best thing to do (depending on circumstance) is to run in a lower gear. Other times OD and a locked converter are just the ticket. Surely....you will not argue this?

Being able to 'choose' and adjust for driving conditions is the reason we have a select-able transmission (OD/TC lock out) to begin with.

 

[CruiserMarine]

The title caught my attention. My LX470 1999 in green! Also my 1999 M3 in Fern Green!

 

[uHu]

Can you explain what you mean by locking up? Why wouldn't it lock up in 4th gear when towing?

This "lock up" concept is confusing...

Converters for beginners, or amateurs like me:
The Torque Converter (TC) sits between the engine and the gearbox. It converts RPM into Torque, to put it simply. It allows the engine to run faster than the wheels, and if you rev the engine to the converter's stall speed, (1800 rpm on mine) you get a very high torque even if the wheels are standing still, or nearly still. (Which is not possible on a manual car, and it will burn the clutch if you try).

You always loose some power in the TC, and this lost power is used to heat up the transmission fluid. The loss will increase with an increase in difference in RPM between input shaft and output shaft of the TC. (Therfore the loss (=heat) is lower in a lower gear)
To avoid this loss, the TC is equipped with a Lock Up Clutch, which locks the input and output shafts of the TC when the torque conversion is not needed. When you drive along at a steady pace, not too slow, not too steep uphill, and not accelerating, the TC will lock. This leads to better milage, and no heat from the TC.

The way the control of the TC Lock Up (LU) is managed in the LC, is that it will lock if the speed is over a certain limit (60 km/h for the hdj100) at a nominal accelerator position. If you floor the pedal, it will go out of LU, even if it doesn't downshift. (If you pay attention, you will hear and feel the difference between a downshift and merely going out of LU, but both gives you increased rpm and increased power to the wheels)

Now, for the 4 speed box, the LU will only happen if you are in the 4th gear (OD) as long as OD is selected. If you turn off OD, the TC will lock only in the 3rd gear. (you can change the valve body if you also want LU in lower gears. Not uncommon in OZ)
The 5 sp box, with the OD on (stick in D), will LU in the top gear (5th, OD) or in 4th gear (only when the conditions are right and steady for some time). With the 5-sp box in 4 (=OD off), it will LU only in 4th gear, and more easily than if the OD is on (D position).

So, if you know what your gearbox is doing, learn it's ways, there is no problem towing while in OD. It just depends on load, acceleration, inclination, etc. But, when towing a heavy trailer, you will always get better engine cooling with a higher rpm, and less heat from the TC. The general "rule" about not using OD for towing, is a good advice, but it depends on a lot of factors. If you are unsure of any of these factors, it is better to just not use OD when towing heavy.
And there is also the saying that it's better for the engine to run at a higher rpm with a lower load, than at a low rpm with high load.

 

[flintknapper]

The title caught my attention. My LX470 1999 in green!

Dang, I like that color green. Never seen that before. Pretty sharp.

 

[ikarus]

I have nothing to contribute about towing... but here's my S52 swapped E30 haha

 

[Eliot]

So I ended up getting the transmission fluid exchanged as a precaution. I also had no idea when it was last changed so I needed a baseline. Looks like it was good that I changed the fluid out based on the Blackstone analysis.

LX470 Transmission Fluid Sample (Blackstone Labs)

• Eliot
• Dec 18, 2017

 

[jhanley]

Okay, I have nothing to contribute with regards to Towing either. But here's my 24-valve swapped E30! (My LX is green)