I think unless your car is over 20 years old, doing a water top up and drain flush is not needed, especially if the coolant comes out clean and clear. Mercedes only requires a coolant flush every 15 years or 250 000km. Doing a coolant flush is more so just a preventative action in knowing your cooling system is in good working order.
What I did on my ML and C240 W203 was drain the system. Then pour 4 liters(1 gallon) of distilled water through the system which helps in avoiding leaving any containments of city water may have behind. Wait another 15 minutes, squeeze the top rad hose and force out as much coolant.
I think avoiding tap water is the best course of action.
Quote:
Originally Posted by bhatt
You are still leaving a bunch of coolant in the heater core by doing it this way.
I usually do the following:
1. Drain
2. Fill up system with water from garden hose to proper level
3. Run car until warmed up. Watch out as the car will overheat quickly with just water in it! Just heat up to normal operating temp
4. Let cool for a few mins, then drain again
5. Repeat steps 2-4 once more
6. Drain one final time, then refill with the specified amount of coolant. Once you have added the coolant, add water till full.
For example: system capacity is 10l but you can only really drain 8l (there is 2l in the heater core). This means you will drain the 8l in my last step, then add 5l of coolant (assuming you want a 50/50 mix). You now have 2l of water and 5l of coolant. So add 3l of water and you're done.
You really only need to measure the coolant. Figure 50% of your cooling system capacity and add that much coolant. Then just keep adding water till the system is up to the proper level. Make sure to run the car for a minute to "burp" the system before you finalize the level.
I usually underfill the system a bit, then let the car cool off overnight in the garage. Before starting the car the next day, I pop the hood and fill up to the "fill cool" line.
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