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Mercedes GL450 GL550 GL350 Transmission Fluid Replacement DIY

In this article I will show you how to replace the transmission fluid in your 2007-2012 Mercedes GL450, GL550 or GL320.  To do this job you will need about 10 liters of ATF, a transmission filter, a fluid guide tube, a torque converter drain plug, new pan bolts and a new pan gasket.  Some older models may also require new oil pan magnets so it is probably a good idea to order two new magnets before you open everything up.  

1.  Start out by draining the torque converter.  To drain the torque converter you will need to remove the rubber plug in the bell housing and rotate the engine until you can see the drain plug in the opening.  I got lucky, my engine turned off in just a perfect position for me to access the plug.  If you don't get lucky, you will need to remove the under car shield to access the crank pulley.  Remove the drain plug and let the torque converter drain completely, it takes a while.  Install a new drain plug and torque to 10Nm.

Mercedes GL450 Draining the torque converter

Mercedes GL450 oil draining from the torque conveter

2  Drain the oil pan.  In order to drain the oil pan you will need to knock out the plastic guide tube that is attached to the drain.

Mercedes GL450 Draining the transmission pan

Mercedes GL450 Draining the transmission pan

Mercedes GL450 Removing the fluid guide tube

3.  Unbolt the wiring harness bracket and move it forward.

Mercedes GL450 transmissin wiring bracket removal

Mercedes GL450 transmissin wiring bracket removal

4.  Unbolt the oil pan, discard the oil pan gasket and clean the magnets.

Mercedes GL450 unbolting the transmission oil pan

5.  Please note the location of the magnets.  Mercedes changed the position of the magnets in order to improve the oil flow.  Some older cars even require the pan to be updated to a new design.  If your pan looks like mine with a taper at the back, your magnets should be in a position pictured.  If you have more than two magnets you need to remove them and leave only two at the  back of the pan attached to the tapered part of the pan.

Mercedes GL450 transmission pan magnet location

6.  Remove the filter, discard and install the new filter.

Mercedes GL450 transmission filter removal

7.  Reinstall the pan with a new gasket, don't forget to install the new fluid guide tube.  There are different colors of guide tubes so make sure you install the same color that was there originally.  Use new bolts.  Torque the bolts initially to 4Nm and than 180-degrees.

8.  To fill the transmission, there is an adapter available.  I don't own one so I found some plastic tubing at the hardware store that fit perfectly into the guide tube.  Fill the transmission with 6 liters of ATF.

9.  Start the car and add another 4 liters of ATF

10.  Remove the oil filler tube and let the excess fluid to drain out.  Run the car through all the gears.

11.  Use an infrared thermometer to monitor the temperature of the fluid that is leaking out of the drain plug.  When the fluid reaches about 45-degrees Celsius reinstall the drain plug with a new copper washer.  Shut off the car and check for leaks. 

Mercedes GL450 transmission fluid temperature check

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