Whew, I feel better now to hear it from you!

I was working on my need change for coolant cardboard sign, already found the perfect street corner to stand on :P

but the radiator, stat housing, heater core is alum.

As someone who helped a friend re-do the head gaskets on tha 3.1 Impala, and watched his father fork over a lot of cash to have the upper intake gaskets done on his 3.8 Grand Prix... I can attest to this!

I love how squeaky clean the cooling systems are on my MB and VWs :)

-J

Answer
 

We are talking of coolant corroding the aluminum cylinder head from the inside = weakening = cracking.

On the OM617 and earlier engines:

IMO; The radiator, thermostat housing, and heater core are extremely rare issues if the coolant is changed on schedule.

My rule of thumb is to drain / flush the cooling system a MINIMUM of every three years, or when the coolant test fails -45° C, regardless of miles driven.
WIS document# WH20.80P-KW00-00z

I have seen many abused engines that have original factory coolant at 250,000 miles, the cooling system corrosion is shocking. Often they require a cylinder head gasket.

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Why wouldn't the coolant corrode the radiator from the inside out being aluminum also? Being thinner metal, shouldn't it corrode out first?

The way I see is like hunter said, its all about changing the coolant....most of us aren't original owners of these cars so we cannot state what has been used in the radiator and what causes what. I just think the coolant happens to be at the wrong place at the wrong time, so we blame the issues on the coolant....when you go to a gas station, they don't have a coolant hose next to the air line....but a tap water hose....I believe that the corrosion happens do to tap water being introduced and the coolant not changed so corrosion builds up....I was also known to just use tap water to top my radiator off......when I got my car, there was clean green coolant in the engine....when I pulled the heater hoses to flush....it was all rusty clear water....signs the mono valve was closed when ever the change occurred...

Answer
 

Part of the answer is metal quality:
* Heat exchangers are much higher quality aluminum.
* Heat exchangers rarely have mixed metals (electrolysis) as engines do
* Heat exchangers are more subject to calcium depositing in the small passages.

I am old school: Here is an example of extreme cleaning on my personal vehicles.

#1. Supplies = a gallon of Cider Vinegar, fresh antifreeze, a small box of baking soda.
#2. Drain the cooling system
#3. Pour in the gallon of Cider Vinegar
#4. Top off the cooling system with water
#5. Take a thirty minute drive
#6. Drain the cooling system
**********************************
#7. Flush the cooling system
*********************************
#8. Drain the cooling system

- - - Neutralize the cooling system - - -
#8A. Pour in four - six ounces of baking soda
#8B. Fill the cooling system with water
#8C. Take a thirty minute drive
#8D. Flush the cooling system
#8E. Drain the cooling system
#8F. Pour in one gallon of fresh antifreeze
#8G. Top off the system with distilled water
#8H. Take a thirty minute drive, expecting to see several temperature guage fluctuations, as air bleeds out of the system.


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Hmmn, so a $400 radiator has higher quality aluminum than the aluminum in a $6000 engine? That I did not expect!

Use test strips or read the voltage present between the coolant and ground. As the corrosion inhibiters wear out or are consumed the voltage goes higher I think..

Yes
 

They compensated by making the engine aluminum cooling system parts much thicker than later models.

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A neat trick I learned from my radiator shop guy, is to put a small piece of magnesium in the cooling system. It somehow counteracts the electrolysis damage that occurs in cooling systems/engines with a lot of aluminum. Also, not to add to the coolant debate (I have not read the old threads on the subject and want to learn), but if not green, what coolant came in the 1980's Diesel MB's? I can see that the newer aluminum head engines probably need different coolant, but the older iron head engines probably came with green coolant from the factory (only coolant available at the time?)....Rich

FYI
 

This is actually a GOOD idea that has been around longer than any of us have been alive.

If you want to research the topic, use these terms:
Galvanic anode
sacrificial anode
sacrificial anode radiator cap

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I'm not sure this is common knowledge but the vast majority of cars built in the last 20 years have aluminum cyl heads running. The vast majority of cars built in the last 5 years have aluminum head and block. The coolant manufacturers are well aware of these facts and design their products accordingly. There is nothing special about the metallurgy in a Mercedes engine. Just change out the coolant every 2 years and you won't have anything to worry about.