This is how you can super flush your system.
taken from :
Citric Acid flush - How to do it right
To start with acquire 1 kilogram or 2.2 lbs of Citric acid. Food or lab grade doesn't matter, its easily acquired on eBay or chemical supply houses...its nothing but good old Vitamin C, used in many things including soap making and is far cheaper than what the Benz dealer will charge you.
Now is a good time to locate your block mounted drain plug which will make each step of this far quicker.
Step #1 - You will need to drain and flush your cooling system to remove as much anti-freeze as possible before you start. You should flush at least three times with clear water. Running the car to operating temp each time and allowing it to cool enough to comfortibly hold the lower radiator hose or the bottom of the radiator between flushes. Make sure your heater is set to run full blast (maximum temp setting) during each and every stage so the heater core is cleaned as well as the radiator, and the engine block.
Step #2 - You need a degreaser. a non-sudsing one. Shout will work as will some dishwasher detergents (properly disolved in hot water completely first) or get Some Prestone radiator flush from the parts store. This will degrease however is too wimpy to do much more than that. How much is enough? I would use a 17 - 20 once container. Better to err or the side of too much than too little and not degrease the system enough. This is a critical step as the Citric acid will not do its job with any oil or lubricants from the antifreeze in the system. Since you are taking the time and expense to to this then it would be best to do it properly. Mix the degreasing agent of your choice and fill the radiator full of water, and run the car at least 20 minutes after it is up to operating temp. Easiest to do this with a short drive. Allow to cool down and flush several times untill the water no longer feels slippery that you are draining. Three times should be enough.
Step #3 - Mix your citric acid (its a dry powder) with 1.5 gallons of hot tap water in a clean bucket or other container. When its been completely disolved pour this mixture into your radiator adn top off with tap water.
Take a drive....of about 30 to 60 minutes duration (with heater on maximum temp) after it is up to operating temperatures, you need to get a good vigerous circulation so idling in the driveway will not cut it.
I would avoid leaving this in the radiator for several days or even over night so try to do this step when you have the time to complete it , and the first couple following flushes within a few hours at most.
When the engine has cooled down drain it well, and refill with tap water run up to operating temp for a few minutes then drain when its has cooled off. You do really want to drain with the block plug removed as well as the radiator drain or removing the lower hose. Sediment or rust flakes will not exit the system via the radiator and trust me there will be a lot. You want to do this at least 3 times and until the water coming out does not have a greasy feel to it...this is very important. If you wish you could also do the next step and disolve 1 lb or baking soda (sodium Bicarbonate) into a gallon of hot water and use this on your third flush. This will help neutralize any pockets of acid that may remain. If you do this step you still must flush at least 3 more times thouroughly.
Step #4 - Refill your cooling system with either Mercedes brand Antifreeze or Zerex G-05 which is the only suitible substitute. Mix 50/50 according to the cooling system capacity of your particular model.
Step #5 Enjoy your drives with less max tempratures in traffic and long mountain grades than you likely had previously.
This is time consuming and will take a weekend to complete....but you will only have to do this once...and it will be a better more thourough flush than any shop will achieve. __________________ Proud owner of ....
1979 300SD W116 1983 300D W123 1975 Ironhead Sportster chopper 1987 GMC 3/4 ton 4X4 Diesel 1989 Honda Civic (Heavily modified)
Section 609 MVAC Certified gearhead