Towing advice to protect the transmission for xDrive35i?

[RhythmMachine]

We had a diesel MB to tow our small camper (about 2500 lbs dry) and it was either spectacularly easy or in limp mode. Car got totaled, and we replaced it with a 2012 X5 but, due to the issues related to diesel emissions systems, went with gas instead. I'll be installing a hitch with the BMW wiring harness/trailer module and coding that in later this month, have a weight distribution hitch to hook it up to the trailer, and I'll be adding a brake controller and have towing mirrors. The trailer is very well behaved to pull... short, which can make backing up go off the rails in a hurry, but I'm very familiar with towing it for the past 4 years or so.

The one thing I do worry about is the transmission... the 3L diesel had almost 400 lb-ft at 1600 RPM, so it could take on some pretty significant climbs by just spinning up the turbo and rarely had to downshift, even though it had a 7-speed transmission. The X5 has 300 lb-ft at a comfy 1300 RPM, but even when driving without a trailer I notice it shifting WAY more then the MB on the same roads/same driving style. Combine that with the 8-speed transmission, and I'm not sure how to best handle it.

I realize that towing will always cause more wear and tear on the transmission, but any advice on how to minimize it? Drop it into manual mode and use that to keep it from hunting on hills (we live near the rockies, so hills are going to be a regular occurrence)? The diesel provided excellent engine braking going downhill as well, and I'm not sure if that will still be the case or if I may need to rely on the brakes a bit more.




Love to hear about any experience you've had. Thanks!





UPDATE: quick summary of what I've learned along the way:
1. Use Sport mode when towing to reduce the number of shifts and wear on the transmission
2. Use M6 when towing to lock in the torque converter and lower transmission temperature, trading off a bit of fuel efficiency for what should be a longer-lasting transmission
3. Get the Dinan Stage 2 Tune software to both improve towing fuel economy and greatly increase the capability of staying in M6 while towing up more significant hills

[ard]

ABSOLUTELY try and prevent the trans from shifting under load.


Consider a tranny cooler. Heat is the killer of all automatic transmissions.


Have you serviced the fluid and filter? Keep on top of that.


I tow with an F250 diesel, so no x5 tales....

[andrewwynn]

I've towed in mountains with 35i. You can get a pretty good feel for if the engine is lugging and I let the car do the shifting using DS when there was a grade of consequence. Up hill or down. I never had to use brakes to moderate speed downhill.

[RhythmMachine]

Originally Posted by ard

ABSOLUTELY try and prevent the trans from shifting under load.


Consider a tranny cooler. Heat is the killer of all automatic transmissions.


Have you serviced the fluid and filter? Keep on top of that.


I tow with an F250 diesel, so no x5 tales....

Haven't done the transmission fluid... still undecided after reading about many cases where people had no issues until doing this preemptively, and had significant problems after. Don't want to end up killing it with kindness...

I do have a BT OBD2 dongle that I used with Torque on my MB to try to figure out why it was going into limp mode, so maybe I'll get that running and see if it can view the transmission temp on the X5. I also have a Foxwell n510 Elite that should be able to do live readings of the transmission temp, but only when plugged in and without the user-friendly dynamic display.

[RhythmMachine]

Originally Posted by andrewwynn

I've towed in mountains with 35i. You can get a pretty good feel for if the engine is lugging and I let the car do the shifting using DS when there was a grade of consequence. Up hill or down. I never had to use brakes to moderate speed downhill.

It makes sense that if I'm shifting manually I should be able to get the engine braking I need. The diesel did it more in straight auto mode, but going into DS should do the trick!

[RhythmMachine]

Originally Posted by ard

ABSOLUTELY try and prevent the trans from shifting under load.


Consider a tranny cooler. Heat is the killer of all automatic transmissions.


Have you serviced the fluid and filter? Keep on top of that.


I tow with an F250 diesel, so no x5 tales....

Hey, another question for you... to prevent shifting under load, would you treat it like a manual box and accellerate to build up some momentum, ease off the gas, then shift into the lower gear?

[RhythmMachine]

UPDATE:


We took our 2012 35ix (ZF 8HP45 transmission) out with the trailer (about 3500lbs loaded) this weekend for the first time. My previous tow vehicle was a 2009 MB ML320, which was a diesel with a 7-speed transmission. Between the lower torque with the X5's gas engine (about 100 less) and the 8-speed transmission, I was concerned about how the transmission temp would be. I also have an intermittent issue where sometimes the gate will open up to let me shift into sport/manual mode, but often it won't, in which case I'm stuck using automatic mode and the transmission is shifting as often as it wants... which is really often.

I had to be in full automatic mode for most of the trip, but was able to get into manual for much of the return. Ambient temps were around 20-25C, engine temps were usually 100-110C, and my transmission temps were usually 100-108C. From what I've read, normal operating transmission temp should be 80-100C, with the max allowed for short duration (like climbing a large hill) is 135C.

Interestingly, after I dropped the trailer off and was driving home the transmission temp had dropped about 10C while I was sitting, but once I started driving it rose to the same levels I had while towing and stayed there... so I'm not sure if it's actually getting any hotter while towing than not.

I expected to see a significant difference when I was able to get into manual mode and reduce the number of shifts, but it didn't have much of an impact.

So, I have a number of questions that I'm hoping those of you with more knowledge and experience will be able to help me with.

1. Should I be concerned about my current operating range? I was consistently running a little above the the high end of "normal", and while there were a number of significant hills (southern Alberta), the ambient temperature was lower than it will be when we're doing most of our towing in the summer. I'm not sure if I was over the normal range because the car couldn't cool it adequately or if it was "intentionally" running in that range, since it didn't continue to climb.

2. I'm at about 160K km on the car and the transmission fluid hasn't been changed (I bought it this past winter), so I have an appointment with my trusted indy shop to get that done at the end of the month. Will fresh fluid impact the temperatures much?

3. When I get the transmission fluid changed, I opted to go with the VF OE oil pan and filter, which is plastic, but several hundred Canadian dollars less than an aluminum model. I've read lots of people saying that the aluminum pan "should" have an impact on lowering the temp, but no real-world input from people who have used both with the same car/similar circumstances. Does anyone know if upgrading to an aluminum transmission oil pan will have a material impact on keeping the temp down and so may be worth spending on?

3. I got a VEEPEAK OBD dongle and Car Scanner Pro to read it to see when the torque converter is locked up, but it doesn't seem able to pull that value even though it lists a sensor for it. Bimmerlink doesn't list that sensor, so maybe it's not possible to monitor. I am able to monitor the transmission's output shaft speed and turbine speed, though... am I correct in assuming that if those are the same, the torque converter is locked? Running in 6th gear at around 100km/h both values were often sitting at 288 rpm, but having it there didn't seem to impact the operating temp much. I also read somewhere that when the fuel efficiency gauge is at about 1/2 way or lower (which, on a Canadian model would be 10L/100km), that indicates that the torque converter is locked, but I couldn't find any way to keep it locked in that zone at highway speed with any kind of incline. If keeping the torque converter locked is important, how can I do that and tell when I'm doing it?

[andrewwynn]

Monitor in/out of xm will tell you if TC locked. You can also check any time with a tiny boost of right foot. The xm algorithm is very biased to keep it locked!

Example if you watch throttle position on bimmerlink and going 65 mph, you can probably go from 10% to 40% throttle with almost no change in RPM.

I teach people the method to force shifts which would be very helpful for you when the E Gate error is troubling you. (More on that later).

If you are climbing a hill or just want to boost your speed 10-15, a gentle push of throttle will always just lug the engine and never down shift, often not even unlock the TC.

Give the throttle a quick jab than drop. Example: if you are at 15% (guess I can't recall what steady state driving is), jab the throttle to 80% than instantly back to 40-50%. You'll get the xm to unlock the TC and and instant downshift exactly as if you put the gear shift request into Ds.

I use that method more often than Ds.

Now back to E gate; a motor prob exactly the same type as in the door lock actuator fails and causes this grief. I was about to pull my gear suggestion input device apart to either fix that motor or just pull the plug on it and manually defeat the gate permanently (you'd have to manually push the gear suggestion lever back to right when done driving before you can start the car (from experience)).

I happened into a replacement gear suggestion input device so I just did a swap and no coding needed I took from a 50i e70 and put in my 35i.

There are videos for teardown. New the part is close to $1000, used they are often $300. Not sure the expected lifespans but it's a common fault so I'd prob tear mine down and fix/hack before paying $250+ for used one. I just happened into a free one so the issue was eliminated.

I had a different problem occur while I was towing: turbo solenoid failed and I lost turbo! Towing though the mountains!

Praise Jesus I had swapped the gear suggestion lever so I could use Ds and on occasion manual shift.

In almost every case, Ds did a perfect job of picking gears and TC lock. I had to MS less than 5% of the time.

The xm of course had the easiest time ever due to the roughly 45hp drop in power. I fixed the turbo for the drive home and what a difference.

If you can't find YouTube video for fixing the E gate send a PM I'll do a little digging.

Swapping it in/out is the easiest repair I've ever done on a BMW in case you can find a replacement.

[RhythmMachine]

Originally Posted by andrewwynn

Monitor in/out of xm will tell you if TC locked. You can also check any time with a tiny boost of right foot. The xm algorithm is very biased to keep it locked!

Example if you watch throttle position on bimmerlink and going 65 mph, you can probably go from 10% to 40% throttle with almost no change in RPM.

I teach people the method to force shifts which would be very helpful for you when the E Gate error is troubling you. (More on that later).

If you are climbing a hill or just want to boost your speed 10-15, a gentle push of throttle will always just lug the engine and never down shift, often not even unlock the TC.

Give the throttle a quick jab than drop. Example: if you are at 15% (guess I can't recall what steady state driving is), jab the throttle to 80% than instantly back to 40-50%. You'll get the xm to unlock the TC and and instant downshift exactly as if you put the gear shift request into Ds.

I use that method more often than Ds.

Now back to E gate; a motor prob exactly the same type as in the door lock actuator fails and causes this grief. I was about to pull my gear suggestion input device apart to either fix that motor or just pull the plug on it and manually defeat the gate permanently (you'd have to manually push the gear suggestion lever back to right when done driving before you can start the car (from experience)).

I happened into a replacement gear suggestion input device so I just did a swap and no coding needed I took from a 50i e70 and put in my 35i.

There are videos for teardown. New the part is close to $1000, used they are often $300. Not sure the expected lifespans but it's a common fault so I'd prob tear mine down and fix/hack before paying $250+ for used one. I just happened into a free one so the issue was eliminated.

I had a different problem occur while I was towing: turbo solenoid failed and I lost turbo! Towing though the mountains!

Praise Jesus I had swapped the gear suggestion lever so I could use Ds and on occasion manual shift.

In almost every case, Ds did a perfect job of picking gears and TC lock. I had to MS less than 5% of the time.

The xm of course had the easiest time ever due to the roughly 45hp drop in power. I fixed the turbo for the drive home and what a difference.

If you can't find YouTube video for fixing the E gate send a PM I'll do a little digging.

Swapping it in/out is the easiest repair I've ever done on a BMW in case you can find a replacement.

This is really helpful - thank you so much! So I'd be able to monitor the in/out based on the transmission turbine speed (in) and output shaft speed (out)? I assumed that when those values were matching up I was locked, but your suggestion of making small throttle adjustments to test it will be reassuring.



A question about this part: "Example if you watch throttle position on bimmerlink and going 65 mph, you can probably go from 10% to 40% throttle with almost no change in RPM." Is this because it's using the turbo instead of increased RPMs to provide more power?


I hope I won't need your technique for forcing shifts if the gate gremlins act up again, but I can't say I'd be shocked if they do. I have pulled apart the shifter assembly once already to address this. I'm not the most mechanically inclined, so I was pretty proud that I got it apart, back together incorrectly, apart again, and back together correctly without losing or breaking any parts, but it's not something I'd want to be doing on a regular basis. Like you, before buying a replacement I'd see if I can just remove the gate completely and, as you said, make sure I push the shifter back to regular auto mode before my wife tries to start the car the next time. If I could be sure that a used replacement would resolve the issue completely I'd be more open to it, but I'd rather not spend several hundred dollars to end up with the same issue before long.



And I feel your pain with your mountain towing adventure. I had issues with the turbo actuator on my previous tow vehicle (MB ML320 Bluetec), which is when I discovered that a 3L diesel without a turbo is a scary place to be on the highway with a trailer.

[andrewwynn]

Funny you mentioned put stick right before wife drive. That was exactly what happened to me. The gate motor went on strike during a drive where I was using Ds and I didn't put it back.

The car simply refused to start. I can't remember what indication let me know over the phone that the gear stick was in sport mode but she had to push the stick right.

As far as the force shift with the heavy quick throttle tap, that's not for exceptions that's for every day all the time.

If you are going 40 and want to go 50, rather than lug the engine in 8th, tap the throttle to break the TC lock and depending how deep you hold it you can get between 0 and 2 quick downshifts just using your right foot.

Example: 15 to 80 to 20% pedal and you can stay in 8th break the torque converter lock and smoothly accelerate with some extra RPM and no lugging.

15 to 80 to 40% you'll get an instant one cog downshift exactly like throwing the stick left.

Then of course pedal to the floor and then just a little more (105% throttle), there's a switch at the bottom where it's suddenly 30% harder to push but goes a little more bmw calls the kickdown I believe: that will do some quick math and determine the lowest possible gear that's possible at thay moment and go directly there for maximum launch. Most BMW drivers are unaware of the kickdown and just do it by accident on occasion.