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Transmission Cooler and Thermostat Replacing
 
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Pelican Technical Article:

Transmission Cooler and Thermostat Replacing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$350

Talent:

***

Tools:

T25 Torx driver, 10mm, 13mm, 16mm socket, flathead screwdriver

Applicable Models:

BMW X5 (2000-06)

Parts Required:

Transmission cooler, bracket and thermostat, fluid

Hot Tip:

Work with a cool engine

Performance Gain:

Proper transmission cooling

Complementary Modification:

Inspect or replace cooler hoses to the transmission

The transmission oil cooler helps to reduce transmission fluid temperature via the engine cooling system. Transmission fluid is pumped through the cooler through one set of channels, while engine coolant is pumped through another set of channels. The engine coolant helps to transfer the heat from the transmission into the cooling system, keeping the transmission operating better. Transmission fluid is extremely sensitive to heat. Fluid performance can drop about 50% with a 20 degree F rise in temperature. Most transmission fluids operate at a temperature of about 175 degrees to 200 degrees.

BMW X5 models have a cooler mounted to the lower right of the radiator on a plastic bracket with a thermostat. The cooler can leak from the fins and the sealing O-rings on the bracket. Remove the lower splash shield and apply pressure to the cooling system. Check the cooler fin area for leaking or signs of engine coolant.

In this article, I'll go over the steps involved with replacing the transmission cooler on BMW E53 X5 models. Be sure to work with a cool engine and confirm the cooling system lacks pressure before opening the cooling system. The subject vehicle in this tech article was an automatic transmission equipped M62 8-cylinder engine. Other models are similar.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Drain the cooling system. See our tech article on cooling system draining and filling.

Remove the radiator cooling fan. See our tech article on radiator cooling fan replacing.

The red arrow points to the transmission cooler.
Figure 1

The red arrow points to the transmission cooler. Remove the lower splash shield and apply pressure to the cooling system. Check the cooler fin area for leaking or signs of engine coolant.

Start by removing the lower splash shields.
Figure 2

Start by removing the lower splash shields. See our tech article on lower splash shield removing. Then place a drain pan under the center of the vehicle. The first step is to remove the cooler lines (red arrows) from the cooler (green arrow).

Press in the release collar (green arrow) and hold it while you slide the hose off the cooler (red arrow).
Figure 3

Press in the release collar (green arrow) and hold it while you slide the hose off the cooler (red arrow). Be prepared to catch any dripping fluid. Remove the line from the cooler (inset).

AST makes a pretty slick tool (red arrow) (# BMW 5346) for removing the lines.
Figure 4

AST makes a pretty slick tool (red arrow) (# BMW 5346) for removing the lines. It goes over the line, holds the collar and allows for easy removal. Not necessary, but when you do a lot of these it's nice to have an advantage.

Remove the radiator cooling fan and shroud.
Figure 5

Remove the radiator cooling fan and shroud. See our tech article on cooling fan replacing. Remove the alternator drive belt and tensioner. See our tech article on drive belt and tensioner replacing.

Working at the right lower side of the radiator, remove the three hoses from the automatic transmission cooler (red arrow) bracket (green arrows).
Figure 6

Working at the right lower side of the radiator, remove the three hoses from the automatic transmission cooler (red arrow) bracket (green arrows). Use a flathead screwdriver to lever out the coolant hose retaining clip. Be sure to pull the retaining clip out until it rests at the stop. Pull the hose straight off the bracket to remove it. See the following steps for details of removing the hoses.

Use a flathead screwdriver to lever out the coolant hose retaining clip (red arrow).
Figure 7

Use a flathead screwdriver to lever out the coolant hose retaining clip (red arrow). Be sure to pull the retaining clip out until it rests at the stop.

Pull the hose straight off the bracket to remove it.
Figure 8

Pull the hose straight off the bracket to remove it.

Working at the bottom right side of the water pump, use a flathead screwdriver to lever out the coolant hose retaining clip (red arrow).
Figure 9

Working at the bottom right side of the water pump, use a flathead screwdriver to lever out the coolant hose retaining clip (red arrow). Be sure to pull the retaining clip out until it rests at the stop. Pull the hose straight off the water pump to remove it.

Working at the bottom right side of the radiator, remove the plastic rivet from the bracket (red arrow).
Figure 10

Working at the bottom right side of the radiator, remove the plastic rivet from the bracket (red arrow). Use a trim panel tool and lever out the center pin (green arrow). Then remove the rivet (inset).

Move back to the top of the vehicle.
Figure 11

Move back to the top of the vehicle. Then disconnect the radiator outlet temperature sensor by pressing the wire release (green arrow) and pulling it straight up. The red arrow points to the lower radiator hose.

Working at the cooler bracket, remove the T25 Torx fastener (green arrow).
Figure 12

Working at the cooler bracket, remove the T25 Torx fastener (green arrow).

Remove the alternator drive belt (red arrow) and tensioner (green arrow).
Figure 13

Remove the alternator drive belt (red arrow) and tensioner (green arrow). See our tech article on drive belt and tensioner replacing.

Remove the transmission cooler bracket with the cooler to the left, removing it through the gap between the crankshaft pulley and power steering pump (red arrow).
Figure 14

Remove the transmission cooler bracket with the cooler to the left, removing it through the gap between the crankshaft pulley and power steering pump (red arrow).

To replace the thermostat: Place the transmission cooler bracket on a workbench.
Figure 15

To replace the thermostat: Place the transmission cooler bracket on a workbench. Have a rag nearby to catch any excess coolant as you work with it. Remove the T25 Torx fastener (red arrow).

Pull the thermostat straight up to remove it.
Figure 16

Pull the thermostat straight up to remove it. Inspect the sealing O-rings (green arrows). I suggest replacing these O-rings. Inspect the thermostat for debris (red arrows). Any debris could be a sign of a restriction in the cooling system. Reverse the steps to install the new thermostat.

Working at transmission cooler, lift the cooler release tab (red arrow) until it stops.
Figure 17

Working at transmission cooler, lift the cooler release tab (red arrow) until it stops.

Then pull the cooler away from the bracket in the direction of the yellow arrow.
Figure 18

Then pull the cooler away from the bracket in the direction of the yellow arrow.

When installing the new cooler to the bracket, press the retainer down (red arrow).
Figure 19

When installing the new cooler to the bracket, press the retainer down (red arrow). Then align the cooler with the ports in the bracket and press down until it snaps into place. Reinstall the bracket onto the radiator. Install the hoses and other items removed during this procedure. When complete, be sure to top up the transmission fluid and cooling system. Run the engine and double check for coolant or transmission leaks. 

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Comments and Suggestions:
Rar Comments: Hi,I have a 01 bmw x5 3.0, I remove both hoses from the transmission cooler..and now I don't know which line goes up or down....please let me know..
July 3, 2017
  Followup from the Pelican Staff: See if attached image helps. - Nick at Pelican Parts
Boots Comments: I found it is cheaper to replace the transmission
May 16, 2017
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it. - Nick at Pelican Parts  
Boots Comments: I have a 2001 x5 4.4i it goes into fail safe mode after driving 10 minutes but before that it drives nice then jumps from 1st to 5th gear
May 16, 2017
  Followup from the Pelican Staff: First check the transmission fluid level to be sure it is correct. Then check the transmission ECM for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
edwin Comments: I have a 03 540i auto m tech it shift fine when cold and warm but when I drive for about over 30 min it start to slip and burning oil smell. and the fail trans light come on. do u think this could be a clogged heat exchanger ? i do see some trans fluid on the trans lines but it's not dripping at idle maybe only when Ian moving. I replace the filter n gasket for trans to.
April 20, 2017
  Followup from the Pelican Staff: You can check trans temp using a scan tool to confirm that is the issue. Most times, slips are caused by pressure losses inside the trans, solenoids, seals or clutch leaks. - Nick at Pelican Parts  
Prezzy Comments: I drove about 700km and middle of that journey the car gave "trans overheat warning". I stopped and let the car cool down then drove another 300 or so kays, warning came back and I parked the car. A few weeks later I started getting the "trans fail safe prog. The car drives fine for about 5-10km then it goes into that mode. How do I replace the transmission oil as I note considerable leak under the car and could it be damaged sensors?
March 8, 2017
  Followup from the Pelican Staff: I would assume your leak is why it overheated, low fluid. Or the fluid overheated and the fluid overflowed due to temp. Start by checking fluid level and then running and checking for leaks. - Nick at Pelican Parts  
nemidoff Comments: Good afternoon.Before performing the transmission cooler replacing I would like to know one important thing, so maybe you can help me with this - I will need to replace the oil pipes as well,so in the moment when they will be unscrewed from the transmission box, should I block both holes in transmission so that all fluid will not leak out of the transmission case?Or maybe it will not leak out at all, because connections are on the top of the transmission case, so I will loose only the amount of fluid in cooler and pipes?

Thank you.
February 11, 2017
  Followup from the Pelican Staff: A little bit will come out, it is a good idea however, to replace all of the fluid if possible when replacing the cooler. - Casey at Pelican Parts  
Rafarin Comments: Hi, the trans oil cooler connector on my 05 E53 3.0 is leaking underneath the expansion tank; at first I thought it could be due to a bad expansion tank. After installing a new tank the leak didn't go away; when the engine idles it doesn't leak but when I drive for about 10 minutes coolant flows from under the expansion tank like a river.
Any idea what might be causing this problem?

Thanks!
January 20, 2017
  Followup from the Pelican Staff: Possible faulty sealing O-rings on the cooler or the cooler itself is leaking when hot.- Nick at Pelican Parts  
Rarmendariz1954 Comments: 2003 X5 3.0 I have water in my transmission and tyranny fluid in my radiator. I was thinking it was the transmission cooler,but now that I see that the heater and cooler share passages not so sure . What is your advice. Thanks
January 8, 2017
  Followup from the Pelican Staff: It sounds like the transmission cooler (heat exchanger) is faulty. Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Rob Comments: Nick,
I've just purchased a 2003 X5 3.0L diesel with auto transmission to tow a boat about 4000lbs all up weight with trailer
I haven't picked up the car yet, but was intending to fit an aftermarket transmission oil cooler right from the get go, before subjecting it to the towing duties.
I've just read this article and was unaware that X5's came with a thermostat controlled cooler as standard, so am wondering if adding another cooler in series would be an issue.
I believe additional cooling would probably be a necessity as I live in Perth, Western Australia, where summer temperatures are regularly 35 to 40 deg C 95 to 105 deg F
Your thoughts?

Rob
January 7, 2017
  Followup from the Pelican Staff: I think you may want to bypass the factory cooler and add the aftermarket model with a higher cooling capacity. When connecting, leave the old cooler in place and only remove the trans lines. I bet if you check with a cooler manufacturer, they may have a kit for doing exactly that. - Nick at Pelican Parts  
Sergio Roberto Comments: Hello
I have 2007 328i, automatic transmissions. At idle, engine cold, one of the hoses of the transmission oil cooler pulses. It is normal? Is it indication of the oil is being pumped?
November 22, 2016
  Followup from the Pelican Staff: Are you trying to fix a problem or just noticed the hose moving? If no issue, it is normal. - Nick at Pelican Parts  
Jfperez Comments: Hello I have a 2001 bmw x5 4.4 that about 3 days ago the "Trans fail prog" came on which caused the Abs, check engine, dsc lights to turn on and doesnt let me access first and second gear. Went to a shop and they want to replace the transmission control module and speedsensors. My question is if its not either of those can it be the transmission cooler? The car has never shifted hard or anything but it does have a small leak that i have yet to check out. Anything helps thank you. Also,is it safe drivingthe car with the "Trans fail prog" on?
October 15, 2016
  Followup from the Pelican Staff: A leak will only cause fail safe it is is great enough to cause a slip. It is not advisable to drive with that fault, as engine power will be reduced. - Nick at Pelican Parts  
Katrhyme Comments: Just had the two lines from the transmission replaced due to a leak. The repair shop failed to ensure the two lines were clamped. First one blew off at the shop as they were bringing it to me. Had to walk it back into the bay. Assured me that all was well and fluid was topped off. That was on July 17, 2016. I did not drive the vehicle much for the next month. At the end of August, I noticed a leak again. Drove it on Sept 2 and low and behold started having transmission problems. Barely made it to that same repair shop. Transmission Failsafe kicked in as I entered their parking lot. Found out the other hose blew at the connection. They again fixed it with no apologies offered. My question is: should I take it to the dealer to ensure that it has finally been fixed properly. Not sure I can trust that shop again.
September 5, 2016
  Followup from the Pelican Staff: That is up to you. You can also try an independent BMW facility. Or ask the shop to show you and review the repair. maybe gain some confidence. - Nick at Pelican Parts  
Fids Comments: Can I run my x5 without the transmission cooler thermostat?
July 6, 2016
  Followup from the Pelican Staff: I think so. Only issue would be the trans cooling would be incorrect, possible shifting issues if temp is too high or low. - Nick at Pelican Parts  
nemidoff Comments: Thank you for beautifull article. I have one important question about picture Figure 16: Where I can get those thermostat orings, what is the product oem code for them or dimensions?Could you please suggest me?I cannor find anything on realoem.com

Thank you,

Arvis
March 30, 2016
  Followup from the Pelican Staff: What is the year and model of the vehicle?

I’m not the best with part numbers.



For an instant response, give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need. - Nick at Pelican Parts
 
Sam Comments: continued from part 1

"...Fluid performance can drop about 50% with a 20°f rise in temperature. Most transmission fluids operate at a temperature of about 175° to 200°."

Your article on this subject corroborated what the other webpage stated by stating explaining the interconnectedness of the two systems.

So per your page I may have a leak somewhere or not. It could easily be that I have just neglected staying on top of checking my coolant fluid and it simply evaporated down to nothing...although could it even do this in a closed system? Either way looks as though it is not a trans issue....thank God!

Thanks for having such a comprehensive website! Keep up the great work!

February 18, 2016
  Followup from the Pelican Staff: I would confirm the coolant isn't mixing with the trans fluid. If not, it may have been related to temp. - Nick at Pelican Parts  
Sam Comments: Dear Pelican Parts,

You guys are the best!

I own a 2006 BMW X5 4.4 with about 98k miles on it. For the past year I have been having an issue with my transmission shifting hard from 1st to 2nd gear...when cold and even when the engine has warmed up, although when cold it would happen on a much more consistent basis. When the car was warm it would happen sporadically. I had resorted to shifting the car in the tiptronic/manual mode to avoid the hard whack sound the trans would make when shifting from 1st to 2nd. Of course I feared the worst, that there was a serious issue with the trans.

A few days ago my "check coolant level" warning came on so I did. Much to my surprise the expansion tank/reservoir was totally empty. I immediately filled with BMW coolant diluted 50/50 with distilled water as the directions on the jug state to do. I have noticed in the last two days since topping off the coolant reservoir that the shifting from 1st to 2nd when in "D" mode is as smooth as ever. Having no idea why the trans shifting issue would be related to the engine coolant level I started doing some poking around the web to see what I could find. I found this site:

https://www.2carpros.com/questions/bmw-x5-2002-bmw-x5-transmission-shifting-problem-v-specfic/page/2

with this mention:
"I have had the same issue with a coolant leak causing problems with gearbox shifting thereafter. BMW wanted to replace the gearbox, then we found a blocked heater hose which apparently feeds the transmission cooler. I recently have had a transmission overheat failure whilst stuck in traffic. All point to the gearbox not being cool enough for normal operation as after 30 minutes of driving I have experience shift problems."
I then did a search for this "x5 heater hose feeds the transmission cooler" and found your webpage:

http://www.pelicanparts.com/techarticles/BMW-X5/104-TRANS-Transmission_Cooler_and_Thermostat_Replacing/104-TRANS-Transmission_Cooler_and_Thermostat_Replacing.htm

with this mention:

"The transmission oil cooler helps to reduce transmission fluid temperature via the engine cooling system. Transmission fluid is pumped through the cooler through one set of channels, while engine coolant is pumped through another set of channels. The engine coolant helps to transfer the heat from the transmission into the cooling system, keeping the transmission operating better. Transmission fluid is extremely sensitive to heat. continued....
February 18, 2016
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 

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Page last updated: Mon 9/25/2017 02:50:57 AM