The trick is this:
1.) First, backflush the system...open all paths/orifices (to the heater core included), and backflush 'til the water is clear...
2.) Then drain everything you possibly can, remove hoses if you have to...
3.) Then appropriately reattach them (the hoses) and close all open orifices...
4.) Fill the system with clean water...
5.) Start the vehicle, let it come up to temperature, shut her down, and let her cool down
6.) Then drain everything again, following the above procedures (Only Steps 1-3) if you have to in order for a complete drain.
7.) Now, put in 50% of the system's CAPACITY of the MB Coolant. Straight. Not premixed. Straight. If the system's CAPACITY is 12 litres, then 6 litres of the MB Coolant goes in.
8.) THEN, you top off the rest of the system w/distilled water.
9.) Start the vehicle and run up to temperature. Shut it off and let her cool.
10.) Then, if you need to add anymore FLUID to the system, add ONLY the distilled water to the radiator neck.
11.) Put only the MB/Distilled Water mix (50/50) in the overflow reservoir.
If you need to use a "water wetter" substance, add it after "Step 7" and before you start "Step 8" for the full amount to be included in the refill/mix.
It's worked for me and everytime a mechanic checks the radiator mixture, 50/50 is the answer on the sheet.
The key is getting the proper capacity from someone who either knows it or directly from the operator's manual, if you still have it. If you can't trust the manual, ask someone who knows...
Remember, there's never a stupid question when it comes to taking care of your Benz, just stupid mistakes and smart@55es that take a perverse pride in their own knowledge and will ridicule anyone they believe to be beneath their level of competence. Ignore those bullies...they've made their own mistakes but are too proud to ever admit it.
Good luck!
