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The white stuff is a substance MB puts in their coolant, I believe that when it is soution with the rest of the coolant, it acts as a luricant of sorts for the water pump. I can't come up with the name of the substance off the top of my head right now. "Cal" something, as in Calcium. Maybe the cap wasn't on tight, or someone topped it off and slopped some and didn't clean it off.
The procedure is a little tricky to do it right.
The drain is on the front side of the radiator on the right (passengers) side. You can kind of see it if you look through the opening in the bumper near the tow hook. On the first few years of production, you had to rotate it 90 degrees and pull forward on it (it has like a tab on the front, not typical looking for an MB). It's kind of a pain to get it popped loose. You can take the lower hose off, but you're not really getting all the coolant out of the radiator, not a very good solution. I have the best luck using a very long needle nose pliers to get it started, then a slip-joint pliers on the edge of the tab to turn it a little further, then pull in it by hand to get the stuff to flow a little faster.
To drain the block, it's easier to do if the right front wheel is off, so I try doing a tire rotation and a coolant flush at the same time, and if you're lucky, it could use a brake fluid flush too, since the wheels are off. If I'm REALLY luck it'll need brake work done too, then I can really multi-task!
Anyways, with the right front wheel off, you can see the block drain in-between the right wheel liner and the top of the frame. It's hard to describe the shape, kind of like the shape of the top of a soda bottle, but small, maybe the size of a thumb from the first knuckle to the tip of the thumb. It's a blueish-aluminum looking also. It's right around the front cylinder and the next cylinder back from the front. The inside of this drain is a 6mm hex. If you use a long 3/8" extension and a 6mm allen socket, you should be able to fit it between the fender liner and top of the frame and get it into the drain. What I usually have to do is go in at an angle (from a slightly forward position), then when i have it just started a little into the drain, pull back on the extension so it lines up better. The extension kind of gets pinched between the frame and liner, but you can still turn the extension with a ratchet no prob.. You then just need to loosen the drain a couple turns and then withdraw the socket and extension so it'll drain out easy.
Once all drained, you can refill it. 50:50 works OK for me. Top it off (it takes alot of coolant). Once the coolant seems like it's full, just start the engine and immediately shut it off again, this will allow the aux coolant pump to run, which will help circulate coolant through the system to help with air pocket removal. I wouldn't try to drive it for about 10-15 minutes, during which you should monitor the coolant level to make sure it's staying up, topping off as required.
Keeping the climate control knob on max heat won't really improve anything as far as circulation, as the ML has no heater valve, it's max cooant flow through the core at all times, and blend doors control cabin temp. However, you can put it on max heat and monitor the vent temp, because obviously if it's on Max heat, and the engine temp is normal operating temp, but cold air is coming out the vents, you know there is air in the heater core. But if you fill the cooling system as I described, there shouldn't be a problem.
Gilly
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