E39 540 Automatic Transmission Cooler Service
DISCLAIMER: I bare no responsibility for damages to you or your car, please use these instruction with safety in mind at all times.
I looked all over but could not find a good write up with pics to help me visualize what need to be done to replace the transmission cooler on the E39 540, so I hope this will help someone do just that. Once you see how easy it is to do hopefully you will tackle the job and save yourself some grief. Read my story in the 4th post below for more info.
The Automatic Transmission Cooler consists of a heat exchanger and a regulator which functions as a thermostat of sorts. IMO this maybe the most overlooked area on an E39 540. Guys replace cooling system parts or the transmission oil and filter but forget about servicing this area. If you take a careful look at the transmission cooler in great detail you will notice that it sit at the lowest point of the entire cooling system and the passages are quite small, keep reading this thread and you will see why I believe this service is important
You will only require basic tools:
-floor jack and jack stands
-lug wrench for wheel lugs
-needle nose pliers
-T30 Torx allen key or socket
-13mm & 8mm sockets, ratchets and a few short extensions
-small flat head screw driver or pick to remove O rings
Required Automatic Transmission Cooler Parts
Qty Discription Part #
1 Voltage Regulator 17211437772
1 o-ring 14,4x3.0mm 11537501777
2 o-ring 14.5x2.5mm 17111711987
1 Heat Exchanger 17217505823 Optional
1 Gallon Coolant
The whole job can be done in under 1 hour.
Last edited by MLue1; 12-23-2011 at 06:44 PM. Reason: Adding info or correction(s)
Start by jacking up the left front (driver’s side) of the car and set jackstand(s) to support the car and remove the left front tire.
Use 8mm socket to remove the fasteners on the left lower fender liner.
Use 8mm socket to remove the fasteners on the left brake duct housing. There is a hidden fastener behind the horn, you can see the hidden fastener by looking through the front grill. (see pics).
Once the left brake duct housing is removed you can see the Heat Exchanger and Regulator.
Recommended procedure (continued):
Locate a drain pan to catch coolant. Remove the front and rear coolant hoses by releasing the wire retaining clips on the coolant hoses. Plug the hose openings with a cloth, I used a bunched up paper towel, it drips a bit but that's why you have a drain pan.
Remove the two 13mm Bolts that secure the Heat Exchanger, the 1st 13mm bolt is hidden behind the Regulator and is oriented towards the front of the car (this bolt is #18 in PartsDiagram A.jpg in post #1). Once the 2 bolts are removed, this allows you to pull the heat exchanger/regulator towards you to disconnect it from the 3rd coolant line. Coolant from the water pump will initially gush out from this line, again you can plug the opening with a cloth or bunched up paper towel.
Important Note: DO NOT DISCONNECT hose 5, 6 from the cooler (in Parts Diagram A). Let the Heat Exchanger hang by the two hoses, unless the Heat Exchanger has to be replaced.
Use the T30 torx allen wrench or socket to remove the three screws securing the Regulator to the Heat Exchanger. Pull up or pry the regulator up and off the Heat Exchanger.
Use a pick or small flat screw driver to remove the o- rings from the 3rd coolant line and from the Heat Exchanger. Clean the mating surfaces and install new o rings.
Lube all three o rings with some coolant, slide the new Regulator into place and secure with the three T30 torx screws.
Line up the Regulator side port with the 3rd coolant line and slide the Heat Exchanger/Regulator assembly into place and secure with the two 13mm bolts.
Install the front and rear coolant hoses to the Regulator. Double check that the wire clips are secured correctly you don't want any coolant hoses coming loose while driving.
Install the left brake duct housing and secure with 8mm fasteners.
Install left lower fender liner and secure with 8mm fasteners.
Add coolant with the bleed screw open fully open (out), complete cooling system bleed prodedure (not included with this write up).
Check for leaks.
Last edited by MLue1; 07-24-2011 at 11:22 AM. Reason: Adding info or correction(s)
My story and other info
My story and the reason that I put this write up togeather. About a year ago last spring my 540iT started down shifting quite hard during stop and go driving; ya I know what you’re thinking but this was like suddenly hitting a wall at low speed, scary as hell when it surprises you. A few times it went into "fail safe mode", and would only reset after sitting for an hour or so. Initially we thought that I need a new transmission and even one reputable shop determined as much. After some research, we concluded that the most likely causes were either the thermistor in the transmission harness acting up or the transmission was worn out and require rebuilding. We ruled out the transmission thermistor, when my buddy David used his INPA software and OBD cable to confirm that the tramsmission harness thermister was operating correctly and that the transmission was not being cooled at all. We monitored the operating temperature of the transmission using a laptop with the INPA software loaded and cable connected to the OBD port inside the car, we watch the transmission temperature climb steadily to 272 degrees F, while I drove around in stop and go traffic, with shift quality degrading as the temperature rose. FYI the operating temperature of the transmission is supposed to be about the same or lower than that of the engine.
When we removed the tramsmission cooler Regulator using the above procedure, we discovered that "cool side" passage on the Heat Exchanger was plugged by a clay like substance (see pic). Basically, the cool coolant from the rad could not flow because of this substance, hence no cooling. I used a flat head screw driver to remove as much of the substance as possible, back flushing initially did not work but back flushing with compressed air got things flowing. I then hooked up a garden hose with a reducer and back flush the rest of the substance, if I could not accomplish this I would have had to replace the Heat Exchanger (BMW Part# 17217505823). As mentioned in an earlier post, the Heat Exchanger/Regulator is located at the lowest point in the cooling system and the coolant passages are small, so any substance in the cooling system will likely wind up in this area.
The +95 degree heat wave the last few days has basically validated the success of the repair, the transmission has gone back to operating as it did when I first got the car.
If you have this or a similar problem(s), try changing the coolant Regulator or service the automatic transmission cooler first. It's better to spent hundred(s)...instead of possibly thousands of $ replacing a transmission unnecessarily.
Symptom of a Transmission Running Hot
-The transmission would down shift un-expectedly with a jolt.
-Holds on to the lower gear when accelerating longer than expected or sometimes down/up shift by itself.
-When driving in stop and go traffic, the transmission will lock into 3rd gear and will shift neither up or down. This is a sign that the transmission is locked into “fail safe mode” in response to an abnormal condition.
Last edited by MLue1; 07-22-2011 at 01:04 AM. Reason: Adding info or correction(s)
Not a lot of space to work in though.
You must like the heat as you picked the hottest week in Toronto to do this!
I find it interesting that is is called a voltage regulator instead of transmission temp regulator.
So does it run like a champ now ?
Great job!! It's wonderful that you stayed with the diagnosis and used applied logic rather than blaming the magical sealed box. With INPA, or any scanner that can access the EGS data stream, monitoring fluid temp is the key. If the temp shows unrealistic spikes up or down, then blame the sensor. If it just keeps climbing, then it's likely the cooler or regulator.
Mods, please put this in the DYI.
most likely the cooling system was filled using regular tap water rather than distilled water which allowed corrosion and scale to form.
Leave it to bmw to complicate a tried and true system. 99% of cars simply use a coil inside the radiator or a separate cooler in front of it(like the earlier 540s and the 528s use, which was simple and bulletproof.
>'97 528i, 200000 miles, Hella Xenons, 17" Stilauto wheels, Vogtland Drop Springs, Dynomax Race Muffler, Homelink, 540 brake upgrade, 15mm spacers >'65 & '74 MG Midgets BFC OT Lego Club #48 Manual conversion in process!!!
This is a very good idea. Range Rover owners have been seeing many failures due to this exact blockage in the tranny heat exchanger. I will be doing this. Thanks for the write up.
Last edited by MLue1; 07-22-2011 at 08:41 AM. Reason: adding comment
Thanks for the great write up! I am going to do it.
Then there's later Chrysler that has the cooler incorporated in the A/C condenser....
So would a '97 540i have this?
Nice writeup, should go into the DIY section!
No current BMWs.
1994 Roadmaster Wagon
1974 Alfa Romeo Berlina
I have a 97 528 that leaks at the cooler, which I assumed would be in the same location as yours. Though the location of the trans fluid puddle suggests it's not. So I took apart the driver side inner fender stuff, and there's no cooler. The puddle is toward the middle/passenger side. If I didn't know the cooler is the same part for 6 & 8 cyl cars, I'd think it was built into the radiator or something.
Maybe the cooler's on the passenger side in exactly the opposite location of yours, but the drip is running towards the center of the car.
Back to the drawing board...
Thanks for the writeup
Anyone here replaced the AT cooling lines (transmission - heatexchanger) on a e92 335i?
I got everything loose but looks like I need to loosen more parts from car to get the lines out and replaced.
Hey Mlue today I started a thread cause my 99 540ia is doing the exact same thing... This is a huge help... I wouldnt mind pinging you before I start this just not sure how to email through this site yet
Thanks so much for this post mlue1. The scenario you presented is very similar to what I am experiencing with my 2003 540 with a slight addition of my ambient or external temperature gauge increasing before the symptoms occur. As an example, just the other day, it was 88 degrees in my little part of southern California...I drive the car in stop and go traffic for about 30 minutes...the temperature gauge starts to rise...90....95....100...bam! Tranny goes hay wire, would take longer to upshift (approx 4500 rmp) then would get stuck at 3rd. Again very similar to what you wrote. Appreciate the time, and let me know what you think.
You should get your thermostat checked out, the mechanical side is actually quite solid unless it is quite old but the characteristic control that is the electrical side fails often (Basically: the heater element that is used to heat the thermostat to allow it to open ealier to cool the engine under certan conditions or for overheat protection).
The engine may run hotter than it should, which will not help the tranny any. You can check the heater with an ohm meter:
1) with the engine off remove the engine cover
2) unplug the plug connected to the thermostat
3) measure the resistance accross the 2 pin connector.
I found my failing thermostat to have a resistance fluctuating between 4~6 ohms cold, the new one out of the box at the same temprature was registering 9~12 olms. My belief is that if the thermostat heater is burnt out and operating at a lower resistance it may draw current from the other systems in the wiring loome, and cause the operating voltage to drop-off as well; this may cause all type of false codes to be generated including tranny codes and others.
Since I replaced my Thermostat, no more false codes.
Last edited by MLue1; 11-19-2012 at 03:25 AM. Reason: adding comment
The normal removal procedure is that on pulls the lines towards the exchanger and then one pushes the plastic clips in. This allows one to slide the hoses off the exchanger. The plastic clips have broken due to the corrosion and so now I have no idea how I am supposed to get those hoses off. Can anybody please assist me with this?
Oh my lord.. I just bought a 2000 540i and this is the only problem with it.
If this DIY fixes it...
Well yeah, you get the idea.
HOWEVER, mine doesn't downshift roughly when the aircon is on..
I'm still doing this DIY regardless, but I'm stumped as to why that is?
New to this forum, I have the same issue. A 01 E53 X5 with a bad tranny issue.
Car drives fine while cold but once the engine is at normal running temp it seems
To chirp on me as if I just got rear ended. So this leads me to believe it might be the heat exchanger,thermostat or oil regulator going bad or clogged as my Trans runs really rough once car is at normal temp.
Question: how to identify if these parts I mentioned might be faulty?Besides the
Obvious fact that the tranny goes to "safe" mode and locks into 4th gear and has
a rough down shift. Thanks in advance.
I cannot thank the guys in this forum enough! OP and Randy, the local resident tranny expert. Fortunately for me I have dodged a big bullet, everybody wanted to rebuild my transmission, and it was low on fluid and then the reg. became bad.