5HP24 cooling: my personal experience

[CMC540]

A huge thank you to jicaino for this info and thanks to CPHES for bumping this thread to bring it to my attention.

My 2001 540 transmission has exhibited the behavior described in this thread twice this summer after several hours of short trips and stop and go driving on hot days. After sitting overnight, everything is fine again. I've been trying to figure out the problem, but searching transmission issues, all I've been finding are threads talking about the Trans Failsafe error. Mine has not shown that message on these occasions or left any codes in the ECM. I had never heard of "thermal protection program".

I was starting to budget a reman ZF transmission but I now think I'm experiencing thermal protection mode. I will definitely try this before springing for the replacement transmission. Thanks again!!

[TiesTorN]

discussions about temperature related behaviour on these trannies are written everywhere. you probably couldn't search it properly.

what jicaino did to his tranny was a good idea but it's not enough. still operating around 90-95c. around 80c is the sweet spot for this tranny. I suggest an aftermarket external cooler on top of the factory cooler as in here;

https://xoutpost.com/bmw-sav-forums/...-solution.html

[Ctcranor]

Great suggestion and as my radiator is out, perfect timing. A few questions for those of us less mechanically inclined:

1) As the cooler sits higher than the tranny and we can’t put it more fluid, and now uses (could take) more volume of fluid, is there any concern with that volume being in the cooler and not the transmission?
2) Is there a proper way to plumb this with a supply and return side? If so, which is our existing supply and return and which goes to the upper and lower lines on the cooler?
3) On the donor lines, should I cut the hose, use a nipple to a new hose or cut the aluminum tube and slide the new hose over that, or does it matter?

Thank you for any insight!

[hugyourewoks]

Great suggestion and as my radiator is out, perfect timing. A few questions for those of us less mechanically inclined:

1) As the cooler sits higher than the tranny and we can’t put it more fluid, and now uses (could take) more volume of fluid, is there any concern with that volume being in the cooler and not the transmission?
2) Is there a proper way to plumb this with a supply and return side? If so, which is our existing supply and return and which goes to the upper and lower lines on the cooler?
3) On the donor lines, should I cut the hose, use a nipple to a new hose or cut the aluminum tube and slide the new hose over that, or does it matter?

Thank you for any insight!

I'll let you know as I am in the middle of it right now

[hugyourewoks]

Great suggestion and as my radiator is out, perfect timing. A few questions for those of us less mechanically inclined:

1) As the cooler sits higher than the tranny and we can’t put it more fluid, and now uses (could take) more volume of fluid, is there any concern with that volume being in the cooler and not the transmission?
2) Is there a proper way to plumb this with a supply and return side? If so, which is our existing supply and return and which goes to the upper and lower lines on the cooler?
3) On the donor lines, should I cut the hose, use a nipple to a new hose or cut the aluminum tube and slide the new hose over that, or does it matter?

Thank you for any insight!

Alright, I'm done with the cooler install, with the exception of adding more fluid. To answer your questions
1) I tried to add some fluid to the cooler after I had installed it in the bracket. One of the hoses was attached. It was pretty much pointless as no air was really able to escape anywhere to allow more fluid in. I'm just going to add more fluid to the tranny in the normal way (level the car, let it warm up, pump in ZF fluid via the shampoo style pump and have ATF run down my arms and spill on the garage floor as per the usual). I know I'll have to do this several times before the air is all out of the cooler. If anyone has any better idea, I'm open!

2) Take this with a grain of salt and a little deductive reasoning. On my 2001 540iT the transmission has banjo fittings for the tubes. I used FCP euro's website to find a replacement "outlet" tube.

https://www.fcpeuro.com/products/bmw...et-17221711465

The tube has that short (maybe 2in flexible rubber) about 2/3s the way down it. The other tube doesn't have a short section of rubber tube. Bam, outlet found; but the cooler was not as easy. Basically I had a hunch that the extra protrusion on the new cooler was some sort of thermostatish type of thing? See my crude drawing of the I6 realoem parts drawing. That's how I based my tube layout. You may point out that the actual cooler looks almost nothing like the realoem drawing and you are correct. See my slightly more sophisticated drawing. Am I right? I have no idea

3) I cut the installed lines (if they weren't leaking already, why change it?) in the flexible part right by the old fluid heat exchanger. Using a tubing cutter, I cut the eBay lines I got right by the first bend on the new air heat exchanger side. After I cleaned the new (old eBay) lines, I shoved them into the cut lines and put a hose clamp on them.

Putting everything back together tomorrow and going to flush my radiator and cooling system with some Liqui Moly radiator cleaner I've had lying around. Meh, why not, I drained everything!
Sorry for the weird photo rotations.

open-uri20141015-21673-1h8959z_.jpg
ATF cooler 6 year old drawing.PNG
Untitled.png
20200929_165016.jpg
20200929_165434.jpg

[Ctcranor]

Ok, finished, easy enough BUT, what am I missing here... I just plugged the back of the alternator where the coolant line used to come out and go the the heat exchanger. My service manual shows 2 coolant lines going to the alternator and I just plugged one...how will my alternator cool without an “open” coolant run? It seems that I have a on ramp but no off ramp!?!?

[Ctcranor]

It looks like there’s another port coming from the cover the housing attaches to. I’m assuming if this wasn’t accurate we would have addressed this by now!

[hugyourewoks]

It looks like there’s another port coming from the cover the housing attaches to. I’m assuming if this wasn’t accurate we would have addressed this by now!

I'm no scientist, but I don't think water anywhere near 100°C would be good for the alternator. I just plugged mine in accordance with the OP.

[CPHES]

This is an interesting convo. I agree that the coolant should have somewhere to go... for the manual, someone who has a late manual needs to get us a pic. I’ve thought of how to make return from the hole we discussed blocking, to the bottom of the rad.

[jicaino]

discussions about temperature related behaviour on these trannies are written everywhere. you probably couldn't search it properly.

what jicaino did to his tranny was a good idea but it's not enough. still operating around 90-95c. around 80c is the sweet spot for this tranny. I suggest an aftermarket external cooler on top of the factory cooler as in here;

https://xoutpost.com/bmw-sav-forums/...-solution.html

After replacing the radiator and having a major drop in temperature in the engine bay, the tranny now operates well below 80°C most of the times. It occasionally spikes above 80° if you're doing full throttle 1/8th mile runs nonstop. As soon as you lay off that it goes back to normal in less than 5 minutes. Also now I have a E6X clutch fan and blades which moves like over 2x what the straight blades in our car does.

[jicaino]

This is an interesting convo. I agree that the coolant should have somewhere to go... for the manual, someone who has a late manual needs to get us a pic. I’ve thought of how to make return from the hole we discussed blocking, to the bottom of the rad.

Sory for the very late response. The coolant is fed to the alternator via a passage cast in the front lower timing cover and gets out thru the top. the back port is there only for the ill conceived coolant/ATF exchanger