X5 4.6is 5HP24 External Transmission Cooler - My Solution
 

Bit of background information to start with.

X5 4.6is done 104k. First time I drove it home from buying it I found it had the harsh 2-1 downshift issue and also came up with a transmission code 'too much slip'.

Car went in to have the torque convertor replaced under warranty and have the transmission fluid and filter changed.

Got it back....and unfortunately the harsh downshift was still there. Checked the transmission fluid which was red (incorrect) and the sump had never been removed so filter had obviously never been done.

After complaining the car went back in to have the transmission fluid changed and filter done properly this time and I insisted they use the proper fluid which they ended up getting direct from BMW (more fool them!).

Got the car back....harsh downshifts were still there although they did seem to not be as bad - might have just been my imagination!

Anyway....I decided to investigate further myself and found that as soon as the transmission temperature rose to above 95degrees the harshdown shifts started.

First port of call was to replace the transmission thermostat which I did but unfortunately it made absolutely no difference.

I then decided that if I was going to make any signficant reduction in the transmission temperature then I was going to have to fit an external oil cooler. So this is what I did.

Parts used...

2 x -8AN Push on fittings (1x straight, 1x 90 deg)
4 x -8AN Fittings (2 x 90deg, 2 x 45deg)
4m -8AN Braided Hose
1x 19 Row Oil Cooler (-8AN Fittings)
1x Mocal 80deg -8AN Oil Thermostat
2x Rubber Bobbin Mounts

I basically cut into the return line of the standard piping system and used the push on fittings to attach to the thermostat then fed the cooler off the other side of the thermostat.

I'll let the pics do the talking...

http://img.photobucket.com/albums/v1...psxbagl5qa.jpg
http://img.photobucket.com/albums/v1...psqjz7munq.jpg
http://img.photobucket.com/albums/v1...psstddzrtp.jpg
http://img.photobucket.com/albums/v1...ps1r0wocgh.jpg
http://img.photobucket.com/albums/v1...psdayti9ds.jpg
http://img.photobucket.com/albums/v1...ps4flvu1hi.jpg
http://img.photobucket.com/albums/v1...psyqcvkjht.jpg
http://img.photobucket.com/albums/v1...psxb8e6lsu.jpg
http://img.photobucket.com/albums/v1...psueidra2m.jpg

...and the real test.

This was before the cooler was fitted - a typical 45 minute, 20 mile journey into work where the last 5 miles is stop/start urban type driving.

http://img.photobucket.com/albums/v1...psgk7d0w4n.jpg

That's the transmission fluid sat at 107 degrees.

....and now after the cooler has been fitted..

http://img.photobucket.com/albums/v1...psimdp8hgp.jpg

That's the transmission fluid at 80 degrees - a differences of 27 degrees!

It usually sits around 76/77 degrees whilst cruising and only rises slightly in traffic - basically sat more or less on the opening temperature of the thermostat.

Has it made a difference to the shifts? Yes, yes it definitely has. Harsh 2-1 downshift has completely been eliminated. All gearchanges are totally smooth and seemless throughout. Massive improvement all round.

Would I recommend this mod to others? Yes I most certainly would. Anything to extends the life of these gearboxes. Even if it means I only get an extra 10k out of it it's definitely money well spent. It's even a good mod to do on a car with no transmission issues - cooler transmission fluid definitely makes for a happier gearbox all round - which is probably why nearly every automatic vehicle since the E53 X5s runs a separate transmission cooler.

wow... I have the same problem ''Lurch'' as we call it.

Very interesting solution... fantastic post! :)

Since mine is being replaced as we speak, I'm thinking about doing this. You're not the only one that has done this and reported good results. Not sure why BMW would think those temps are OK for a transmission, but, nobody's perfect I guess?

Seems relatively cheap compared to a new transmission.

I did not expect such a crazy temp drop with a cooler. Simply amazing. But don't we have a transmission cooler already. I know my face lift 4.8is does.

Yes we do....a losely called transmission cooler when in actual fact it's more of a fluid to fluid heat exchanger.

I fail to see how the standard transmission cooler can work at all well given that fluid that's supposed to be using to cool the transmission fluid with runs at temperatures of 105 degrees and over in normal running conditions.

On the 4.8is the coolant systems runs significantly lower and thus I imagine so will the transmission fluid - another possible reason why you hear of less problems with the 6HP24 boxes than you do with the 5HP24 boxes as they run cooler.

When ambient air temps get hot like the state of Texas liquid cooled heat exchangers are far more effective than the liquid to air heat exchanger.

By the way what is the temperature where you are and while you were taking these temp measurements?

We aren't so lucky to enjoy temperatures such as those you are referring to over here in the UK.

Ambient temperature at the time was around 13 degC.

Also, if anything the hotter ambient temperature would have a slight knock on effect with transmission fluid temps anyway - it won't run any cooler thats for sure if you're 10-20degs hotter over there no matter how effective the heat exchangers are.

Excellent post! Link to where you bought all the supplies, and maybe better pics of where you mounted everything up?

I deal with a lot of European vehicles and VW had a BIG problem with the valve bodies prematurely wearing the spool valve bores. Many of the problems started at early as 60k miles.

The problem was very harsh downshifting once the trans fluid temperature got pretty warm. The warmer the harsher downshifting.

I do not have a lot of first hand experience with the transmissions in the X5, but I also wonder if a trans control module update could help.

Also noticed your engine coolant temp is 226F/108C. My 4.8l E70 ran at the same temp. I was not so happy with this "excessive" temp situation.

I installed a Hamburg Technic 90C thermostat and have been very happy with the current engine temp. Would prefer a 95C stat, but 90C is far better than 108C.

Might want to consider the 90C thermostat.

I am curious as to where the temperature sending units are that are being measured. Most of the time, sending units are located where the highest temperatures will be found, prior to the radiator/heat exchanger. I understand your concern and we always tend to think "cooler is better", but as long as the fluids in question are adequately cooled before going back into the engine or transmission, their performance shouldn't be compromised.

2002 X5 3.0 289,700 miles
2004 325i 123,000 miles