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How to Replace Your Oil Cooler Lines


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All parts used in these pictorials are available at the diesel parts for sale page


Mercedes Oil Cooler Line Installation

Safety and security tips:

Please remember to recycle all your used fluids at an appropriate recycling center.  Be mindful to not spill or splash fluids on yourself, others or the ground.  Also as a safety tip please remember anytime you are working on, around or under your car, to wear safety glasses and secure the car with wheel stops and approved jack stands!  




The following pictorial was completed and donated by Kevin Locke of Texas.



After 20+ years the oil cooler lines become brittle and in flexible.  Mine were sweating oil.  There was always a black spot where I parked, and the girlfriend did not want to see the Mercedes at her house again.  Time to change them out.  You can pay a mechanic 4 hours labor ($350 – $400) or do it yourself.




Parts needed: Both oil cooler lines.  2 motor mounts.1 engine shock (2 is better).  8+ quarts of oil, 1 oil filter, 2 rolls of shop towels, one special tool.  Probably take less then 6 hours using this guide.  That’s like paying yourself $50 per hour!  




The special tool is a 1 1/16 closed end wrench that is opened up enough to allow the metal pipe to pass through, shortened to allow use on the lower fitting at the oil filter, and has one side of the box shaved to allow it to fit between the lower fitting and the fuel injection system.




(Dieselgiant - The above 3 pics show a typical leaky oil cooler hose.  If your car is leaking in this critical area then don't let it go!  It only takes a few seconds to empty the engine of all the oil at highway speed, then its engine rebuild time.)



Lets get started.

 Remove and recycle the old oil filter.

 Drain the oil, and recycle.

 Remove the air cleaner housing.  Inspect element and replace as needed.

 Block the rear tires.  Jack the front end up (a lot) on some high quality stands.



Find a healthy block of wood.  A 2” x 6” that is 14 inches long will work.  Use the wood with the jack of your choice.  You will be lifting the engine.  Place the wood between your jack and the oil pan


Loosen the bottom bolts of the engine mount.  This is an 8mm hex bolt that is located in a hole in the cross member.  Very simple to find, remove the bolts from both mounts.

Raise the engine.  Just jack it up until the fan blade hits the shroud.


Remove the 2 upper bolts on the motor mount.  They are 6 mm hex bolts.  You can see the outboard bolts, the inner bolts are by feel, but come out easy enough.  At this point you should be able to remove the mounts.  You might need to raise the engine a little more.  Remove the fan shroud if needed.  Pitch the old mounts.





On the left side you will also need to remove the engine shock.  Two small bolts on top, one on bottom.  ( view with new lines in)

I had to use vice grips to hold the shaft while I unbolted  the lower bolt.  Remove from the top.  Pitch the old shock




View with the motor mount removed.



Remove the two brackets holding the oil lines.



Remove the bracket from the engine block




Use your special tool to unbolt the fittings.  (Dieselgiant -Be very careful when removing this fitting.  The aluminum can corrode and cause the oil cooler damage.  Liberal use of PB Blaster will help.)

The lower line will drain the contents of the cooler, so be prepared to catch the old oil.






1.    The filter side of both lines will drain when they are tipped down the first time.  Have your catch pan ready.

2.    Both hoses come out to the rear and down.  The lower hose is simple, and should make you feel very confident.  The upper line will have you cussing in German.  I cannot give you any Rubik’s cube solution, you just have to keep twisting and pulling.  It kisses the transmission on the way out the back.  No force is required.

3.    Remember how the lines came out?  Reverse to install.  The upper one first, and it is a bear.  The frustration level may be a little high for the in/out of the upper line.  It is hard.  The lower one is simple (in comparison) .

4.    Get the lines where they belong, and hand tighten the nuts a few turns.  Replace the two brackets, and slowly tighten them down.  Make sure the oil lines are not binding up anywhere.

5.    Tighten all four nuts on the oil lines.

6.    Replace the motor mounts.  The left one had to go in from the bottom rear.  Bolt both to the frame.  Make sure the engine mount will comfortably settle in the center of the mount.

7.    Replace the engine shocks with new ones if needed.  Mine were not doing anything, other then weighing the car down.  Best to replace as a pair. 

8.    Slowly lower the engine back on to the mounts.  This was an easy thing.  Then replace the lower bolts.

9.    Drain the oil again, there will be a little more that will come out.  This is a good time to replace the oil pan gasket, and possibly the oil pan, just look for excessive dents and nicks.

10.  Fill with 8 quarts of your favorite diesel oil.  The oil filter assembly has a thermostat in it that will not open until something like 125C, so you need to get the oil up to temp before the cooler will fill with oil.  You may  need to add more oil after this happens, wait at least ten minutes before checking the level after the engine has shut off in order to get a good level.  Check for leaks.