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Mercedes Cooling System Citrus  Flush


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Mercedes Cooling System Citrus Flush



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! 


I get questions all the time about the cooling system citrus flush, how do I do it, how much etc.  Well I hope to shed a little light on the matter to make it easier for you to do this necessary procedure. First lets discuss why we do a citrus flush.  In a nut shell, its a way to gently remove the rust and scale deposits that will naturally build up in the cooling system of the engine.  Why does rust and scale build up in the engine?  Because water plus oxygen plus iron equals iron oxide or rust.  Antifreeze has corrosion inhibitors in it but most people do not change the coolant often enough over the life of the car, hence the rust starts to take hold.  Not only is there going to be rust in the engine itself but also in the heater core, the radiator and  the piping that carry the coolant too and fro to its various destinations.  Mercedes is one of the few automakers that actually values the citrus flush and I think its a great tool in your quest to make the car live a longer healthier life.  Over the years I have seen MB diesels with so much rust in the coolant that it looked like coffee or muddy water and was amazed that it did not die long ago. 

I recommend that you do this procedure once a year for the first 3 years, then every 2 years thereafter.  The reason is that it takes about 3 flushes over a period of time to reverse the neglect of several decades.  If you happen to be one of the rare owners that actually have had this done on a regular schedule, then once every 2 years will suffice.  So lets roll......


This is the citrus flush from dieselgiant.com that we will be using and......


....the brand new t-stat and seal....


...and a brand new radiator/expansion tank cap.


Procure a bottle of liquid shout gel from your grocery store.  Do not use laundry or dish

detergent or you will never get all the bubbles out of the engine.


Trusty 3/8 inch drive ratchet with a swivel joint will help you along.



To make this job go easier, you will want to remove the t-stat housing.... 



...then remove the t-stat which will allow the flush to circulate immediately.



Remove the housing and remove the t-stat but leave the O ring in place and replace back on the engine.


Just snug it up.


Drain the radiator into a suitable container and dispose/recycle  in a lawful manner.


When its almost down to drops, then reinstall the radiator plug and move on to the block...


Remove the block drain plug on the passenger side of the engine near the starter.



Let it drain into your pan.  Don't skip this step!  You can't get all the coolant out of the block

unless you drain it.




Now on to the fun part.  In order it rid the system of coolant you must disconnect several hoses so that each

area can be flushed with water.... 



The large hose on the drivers side that goes into the head and to the firewall will need to be removed

from the head.  Its right next to the oil filter....


Remove the upper hose at the heater core right next to the throttle pivot bracket  see

all the rust and sludge in the pipe.  Its in the entire cooling system....


Remove the hose that goes into the aux. coolant pump on the passenger side inner fender..


Remove the upper radiator hose and then start flushing with your garden hose.  You will flush

every hose you just disconnected, into the hose and then into the component the hose was

attached too.  Fill the radiator with water until the block drains clear...


Clear water running out of the block..


Flush into the upper hose several times....


Flush the head hose and then the heater core pipe.  Again flush every hose forward then

backward into its component.  After everything is absolutely clear, then hook all the hoses back

up and get the shout ready.



Mix up 1/2 of the bottle of shout in cold water and mix very well in 2 gallons of water.  Then

pour in the radiator.  What???  Yes you must degrease the engine internals and this is

the procedure in the MB factory manual.  This will get rid of any oils that may be present in

the cooling system.  Then top off with water and start the engine.  Run for about 10 minutes

with the radiator cap off and reflush.  You will need to flush about 2 times to get it all out...



Next mix up the entire bottle of citrus flush in 1 gallon of warm water and mix until dissolved.

Pour this in your radiator and top off with water.  Run for about 10 minutes

with the radiator cap off and re flush.  You will need to flush about 2 times to get it all out.

Then make VERY sure that nothing but clean clear water comes out.  You want to make

sure all the flush is out of the engine.  Tighten all the hose back up and double check to make

sure.  Go ahead and install your new t-stat and seal at this time.   To be sure the next step is the

one that is the biggest pain.  The MB diesels are tough to remove all the air from, so I use a

vacuum system that remove 100% of all the air the first time.



By using the airlift and getting all the air out, I can also check for leaks BEFORE I put a drop

of coolant in the system.  If there are leaks then it won't hold a vacuum. 

******If you don't have this system then don't worry, just keep in mind the car is like a baby

it need to be burped to get all the air out.  Just refill with coolant and make sure the front end

 is up on ramps which will help to get the air out.  Run a little while and then stop the engine,

then add more coolant, then run again etc.  Takes a few cycles.




I get the vacuum down to about 26 hgs and let it sit a few minutes...



Then I turn a lever and the coolant I had ready in the white bucket gets pulled in the engine

and there is absolutely no air in the engine.  Fastest fill you will ever do.  Takes about 30 seconds.

Which ever way you choose to replace the coolant, run the engine and check for leaks.  I noticed

that after doing the citrus flush, the overall engine operating temp went down over 10 degrees. 

This tells me the rust and scale does have a significant impact on the operating temps.