Bi-metal engines & coolants

[thysonsacclaim]

I was reading some general things online about bi-metal engines, coolants etc and I thought I'd share my thoughts here (and there, too). I posted this for the help of people on another forum, but I figured I may as well post here, too.

Firstly, the 116 contains two primary metals that coolant will come into contact with: iron (Fe) and aluminum (Al). Most any time you put two unlike metals together, with a solution that has ions in it (dissolved substances) between them, you will generate a current. Add this to the fact the the block is further negatively charged because the Cathode (negative pole), you are essentially creating electrolysis (or think of it as a battery, it IS creating charge).



Some background: the Cathode is negative, the Anode is positive BUT cations are positive and anions are negative. They are given these seemingly differing names because cations are attracted to cathodes and the same with respect to anions and anodes. Cations (+) and anions (-) are the charged atoms which float in a solution. If you take a battery and connect one terminal to a light and place the other in a solution of salt water and then place another wire in the salt water and connect that to the bulb, it will light up.

Adding any soluble ionic substance to water will make it capable of holding a charge, it will ALSO alter the properties of the solution (these properties are called colligative properties). Adding salt results in freezing point depression (lowers freezing point, thus we salt roads) and boiling point elevation (thus you may add some salts to something to make it boil slightly slower). The more dissolved substances, the greater effect. This will increase until the solution is saturated and cannot take any more salt.

See salt:



On the right, salt is in it's crystal form, but on the left it is broken apart. This is what happens when you pour salt into water: the salt molecule breaks in half. When you run current through it, the positive and negatively charged atoms line up to conduct this charge for you. This is why you do not want dissolved substances in solutions that are not supposed to conduct a charge and this is why M-B (and other makes) made a special coolant. This coolant partially acts to inhibit electrolysis!

Salt in water:



In the case of our engine, the aluminum will then become the sacrificial anode (also called galvanic anode). If you think about marine technology, Zinc is often used as this sacrificial anode and becomes corroded and essentially destroyed in order to save whatever metal we do not want to corrode. Heat and movement, both of which occur in the cooling system, will speed up corrosion. What's the first thing you do when you want to combine things faster? You heat them and mix them.

But wait! We don't want the aluminum to corrode in the 116! We need BOTH of the metals to maintain integrity. In order to do that, you absolutely must use the correct coolant and using solute-free water is a good idea as well. It will depend on the quality of the water in your area and it is possible the M-B coolant may inhibit electrolysis enough to prevent any problems (we'll never know for sure, most items like coolant don't list full ingredients). If you use a water softener, I would not recommend using that water at all because it will contain a salt, which breaks into cations and anions (either Sodium Chloride or Potassium Chloride). At my home, only the indoor water is softened.

It is better to err on the side of caution. You can see this particular one says anti-corrosion coolant:





This is not as important for people with single metal engines, or if the radiator is not aluminum, but for those with bi-metal engines, I would rate this as fairly important.


This is really just informational, and if someone down the road signs up and asks if they should use it, now they can know why they should use coolant formulated for bi-metal engines (like M-B 116 coolant).

[WGB]

Don't forget that the radiator in a 116 is copper and you have a third major metal.

Bill

[thysonsacclaim]

Very good point, Bill.

So actually we could call it a tri-metal system! This definitely makes the effect more pronounced.

The aluminum would definitely be first to be affected, between the other two I'd assume the copper. Iron, being negatively charged directly, wouldn't be so highly affected as the other two.


It's interesting because I was responding to some kind folks who thought M-B only made this coolant to gouge people into buying a 'special' coolant that costs more. In reality, I think they just wanted to ensure our cars would be well maintained  


EDIT:

This instance is, I am sure, why some 116 poorly motors have "rotten heads." The direct contact of the aluminum and iron sacrifices the aluminum, and causes it to, soften, powderize and crumble.

[Big_Richard]

arent the upper and lower tanks on the copper core brass ?

they certainly look that way when you strip the paint off.

brass being a alloy of copper and zinc, well, that adds another metal to the mix

[WGB]

And I imagine there is some zinc in all the alloy castings as well plus the brass/copper in the heater core.

I am looking through the maintenance schedule for my E500 and the coolant is apparently only scheduled to be changed every 15 years.

Bill

[Big_Richard]

thats some f-ing long life coolant.

is it the same stuff that we can put in our cars ?

[WGB]

I assume so.

Probably won't be my problem if that is the case.

Bill

[thysonsacclaim]

I trsut the M-B coolant. Especially now since my head was apparently rotted (it had green crap in there when I got it).

[TJ 450]

Yep, it really makes a mess when you use a coolant that isn't suitable.

Tim

[oscar]

It's interesting because I was responding to some kind folks who thought M-B only made this coolant to gouge people into buying a 'special' coolant that costs more.

Guilty here!  I just assumed a good coolant would do and thought the MB Blue stuff to be a nice-to-have but not necessary.  I need a flush.

[thysonsacclaim]

The thing is Oscar, I don't know how it is in other countries, but here they aren't required to list ingredients for anything that isn't for human use. So drugs, food, vitamins, some cosmetics and supplements all get all their ingredients listed and you can compare and see if they are the same deal. Like with generics, most always they have the same ingredients (sometimes slightly different). But at least you can read the label and find out.

Coolants, gasoline, additives, etc etc on the other hand, well we know M-B says it is "anti-corrosive" and I believe that because of the various metals you see interacting together. But regular coolant? Well, it could be the same or not! You can't tell because you can't see all the ingredients on the label. There may be some other brands which are meant for these situations, but I don't know what they are and if they are meant for it, they ought to be labeled as such.

I have seen labs do comparisons between gas additives like STP Carburetor Cleaner vs STP Fuel Injector Cleaner vs STP Octane Booster. Guess what? They all had the same stuff! But they certainly don't cost the same. Booster runs $7, FI cleaner about $5, and Carby cleaner just below that.


Here they might say: "Poisonous: Contains Ethylene Glycol!" or "This product contains lead, known to the state of California to cause cancer and birth defects." Okay... and what about those other 90+/-% chemicals?!

You never know, so you just have to use your best judgment.

[ponton]

It is apparently quite complicated.  Just read this article at popular mechanics...  http://www.popularmechanics.com/cars/how-to/products/1272436

[carl888]

Curious, what's the advantage of the MB coolant?  Surely the blue colour or the green colour is simply a dye?

You can buy green coloured coolant that apart from being anti-freeze, is also a corrosion inhibitor AND sulphate free. (I think that's the term) so suitable for steel/alloy engines.

Regards,

Carl.

[WGB]

Curious, what's the advantage of the MB coolant?  Surely the blue colour or the green colour is simply a dye?

I don't know what the advantage in the colour is but M-B provided an amber coolant for more than two decades which I last saw used in a 2002 ML270CDI we purchsed new. Accoprding to "Mercedes Enthusiast" magazine some years ago the amber coolant was phased out because it caused the aluminium radators to slowly silt up which actually did happen to me during my ownership of a 1987 126 300SE in 1990 or thereabouts.

In the later 90's and obviously ongoing until after 2002 the coolant in the new cars was gradually replaced with the blue coloured coolant and at the same time the top of the plastic reservoir changed from clear to black. My 2003 W211 E320 had the black topped reservoir filled with blue coolant.

Apparently the blue coolant is not considered compatible with the amber and careful flushing must be done if changed over.

Anyway the blue is teh only genuine coolant available now afaik.

Green - wouldn't have a clue if it is any good. My car came full of green and the first thing I did was drain it, flush several times with distilled water and fill it with genuine M-B blue and distilled water 50:50.

Bill

[TJ 450]

The blue is simply a dye, so that the coolant can be differentiated from the others.

Valvoline/Zerex G05 is green (I think), but meets MB standards (says so on the pack). It is also compatible with the Volvo branded coolant, which is dark green from memory. Volvo also either used alloy heads on iron blocks or all alloy engines, all of which are very sensitive to electrolysis and incorrect coolant chemistry.

The issue is not only encountered with MBs.

Tim