I noticed my friends ml has white hard stuff stuck on the sides of his coolant reservoir! wierd.. i suggested to him to do a coolant change and to clean the container as well! but how do you do a coolant change on a ML? i'm guess its like every other car.. remove radiator drain plug, and add 50% water and 50% mercedes coolant into the reservoir with the heater temperature set at max? or do i have to remove the thermostat and remove the upper hose? thank you

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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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No one can explain it better than you can gilly, you should become a teacher for automotive or mercedes benz hahah.. so that explains the white stuff in the coolant reservoir.. it looks a bit like carbon, in my opinion.. the coolant doesn't have to be changed that frequently.. I've seen lots of cars at my shop who never changed the coolant in the last ten years.. maybe they would replace a radiator.. or thermostat.. or even the heater block occasionally.. I know its preventive maintenance.. I remember you mentioned every 3 years coolant should be changed.. do u agree with this? from your instructions that means i don't have to remove the thermostat or open the air bleed valve.. this sounds very easy! haha thanks for your quick response...

99 ML 320

Found this old Gilly response while reading up on a coolant change.

Even after reading Gilly's description, I can't put my eyeballs on the drain on the bottom of the radiator. I have a brush guard on but it does not obscure the view through the opening with the tow hook. I just don't see anything in there that looks like the drain.

Anyone have a drawing or pic showing the location of the drain?

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Even though there is a drain on the bottom of the radiator, most folks just pull the lower hose. My 2 cents.

Thanks Azinn. But since I don't have a record of when it was changed last and the truck has about 225K miles on it, I'd like to drain as much of the old coolant as possible. Still looking for the radiator drain.

Is it on the bottom of the radiator or on the front near the bottom?

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They say its on the bottom. After going out and looking a my radiator I sure don't see it. I would think pulling the lower hose and putting a hose with running water running through the radiator for a few minutes would do a good job of flushing out all of the old coolant. My 2 cents.

don't matter, the drain plug and the lower radiator hose are in the same position, one in front and one on the back. You will drain out the same amount regardless of turning the plug or pulling the hose. There will be a quart or 2 of fluid left in the engine block. unless you open the block drain, which is another PITA to get at.

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98 ML320 (gone but not forgotten)

It faces the front of the vehicle, over on the right side (passengers side), it is almost always red plastic. It is hard to turn, but you turn it 1/4 turn ccw and then pull it out, towards you. CAN be done with a brush guard, makes it even worse though.
Use MB coolant or Zerex G05, which the big box stores usually have.
Gilly

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Photo of drain plug in this thread http://www.peachparts.com/shopforum/showthread.php?t=232573

I finally got around to replacing my coolant in my 99 ML 320. I could not see the drain plug through any opening in the bumper. The one farthest to the passenger side is blocked by some hardware that looks like it secures the plastic bumper to the car. The drain is directly behind that opening. You can see past the tow hook in the second opening in the bumper, but the drain is no where near that. Here is what I see when I look:

[IMG][/IMG]

So took off the right tire and I could see the drain from the rear right side. I could barely get my fingers on it. I worked with some long needle nose pliers and a small pair of vice grips to turn the drain CCW from the side. I believe I had to turn it a full 360 degrees before I could pull it out.

Here is a shot of the drain from the right front tire well:


It took 10 or 15 minutes to drain. Closed the drain with the same tools. Then I added 7 quarts Zerex G05 and 2 quarts water through the overflow tank on the firewall while running the engine. This took another 15 or 20 minutes. I squeezed the upper radiator hose occasionally to try to get the air to rise up into the tank.

I was expecting to be able to add more water, but evidently I left close to 3 quarts in there since I didn't take out the block drains.

Thanks for everyone's help.

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Tks for the write-up, is good info for taking on such a fluid change.

Correct me if I'm wrong...believe the water to be used when mixing with coolant is not tap water but rather distilled water as per MB. Too many unknown elements in tap water.