The reason that there is no DIY on this, is because it is such an easy job. The confusion about the drain plug stems from 2 reasons: (1) Some people are referring to an engine drain plug while others refer to the radiator drain plug. I've never found an engine drain plug on the M112 engine and basically I wouldn't bother with it in any case - just another possible area of complication. The location and appearance of the radiator drain plug may vary slightly depending on where the radiator was sourced from. But it is normally a plastic plug, sometimes with butterfly arms attached to it, but most of the time just a slotted plastic plug that you unscrew with a large flathead screwdriver - or even a coin in a pinch. It is positioned at the lowest point on one of the two vertical tanks on the side of the radiator. Once again, it may either be pointing to the front of the car, or back into the engine compartment.
To change the fluid, warm the engine until the temperature guage shows about 60 degrees, with the heater controls switched to high heat. Switch engine off. Remove the expansion tank cap. Unscrew the plastic plug and catch fluid so that you can dispose of it later. I also blow into the expansion tank to empty it from old fluid, since it will not drain completely. (Hope you have good lung capacity
). Close drain plug. Fill with distilled water if you can find it cheap. In the US it is less than $1 for 4 liters. This is probably only critical if the area you live in has hard water (water with high mineral content). Close drain plug and refill the radiator through the expansion tank. Start engine and warm it up again. Monitor expansion tank and fill up as needed. Once engine reached normal temperature, switch off and repeat steps above. Repeat the process a few times until clear water runs out.
For the final refill, you MUST
use the approved additive. It is not the standard anti-freeze, but a special HOAT type. Mixing another additive with the special HOAT type can result in a nice thick slurry blocking all cooling passages. The additive used by MB is also available as Zerex G05. You can also inquire at the BMW dealer or the VW/Audi dealer as I think they use the same type. The color is NO indication of whether it is the correct type, some times it is green and some times it looks just like p*ss. You will need two cans.
For the final refill, distilled water is essential for a good job. If the fluid is not pre-mixed, then create your own pre-mix with the distilled water in a 50/50 mix. The mix is NOT for low temperatures in your case, but purely for anti-corrosion and anti-cavitation purposes. Refill the radiator through the expansion tank to the correct level with the mixed fluid, start the engine and let it get to normal operating temperature. Add more pre-mix if needed. Now replace the expansion tank cap, go for a short drive and then let the car cool overnight. Check the level the next day before starting the car and fill with pre-mix to the correct level if needed. Repeat this step every morning for a few days, since trapped air may still escape for some time.
After that, you're good for a couple of years again.