Hi Group,
I am flushing my radiator and am replacing the coolant with MB coolant. Seems that several people say DON'T USE DISTILLED WATER and others say USE ONLY DISTILLED WATER. Any MB techs that can solve this dilema?

Thanks,

John
Johneb48@hotmail.com

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John B

There's been lots of heated debate on this forum and others on the merits and pitfalls of using distilled water. The talk is about as passionate as what you read in an oil thread.

I believe the debate is in favor of using distilled water when convenient, and staying away from "bad" water such as well water or water from a softener. Though some will point out that distilled water may start stripping metal ions from engine parts, mixed with coolant this phenomenon goes away.

You can access some of the previous discussions with a search using the words "distilled water".

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95 E320 Cabriolet, 169K

This argument is total BS. I'm an engineer at a nuclear power plant. Corrosion of nuclear safety related steam piping and of the pressure vessel and internal components is a HUGE concern for us, obviously, as there is not just a huge capital investment, but public safety involved as well.

We constantly run a portion of our coolant water through a series of filter / demineralizers. Disolved ions in water CAUSE corrosion. Our license regulates us to shut down if the ion content of our water gets past a very conservative limit, measured by the conductivity of the water.

Those that make this argument don't understand the mechanisms of corrosion. Metal surfaces exposed to a water environment develope a passive corrosion layer, very thin, that actually protects the metal underneith. One of the toughest and best protecting oxide layers is aluminum oxide BTW. Anyway, we go to great lengths to protect this passive corrosion layer by carefully controlling the pH (slightly toward the acidic side of neutral) and mineral content.

The other issue, addressed here, is that minerals form hard deposits on heat exchanger surfaces called scale, which degrades the efficiency of the heat exchanger.

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On the plains of hesitation bleach the bones of countless millions who at the dawn of victory, sat down to wait, and waiting -- died

The trick is, of course, creating and maintaining the proper conditions for the protective oxide layer to not only form in the first place, but to preserve it. The primary and secondary sides in a reactor/steam generator/turbine system all require different chemistry to maximize system life because of different materials predominating in the different systems.
I remember the protective oxide layer on the body and structure of my old Alfa Spider just kept getting thicker...

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'96 C280 (gone)
'97 C36
'05 C230k

One of the reasons aluminum oxide is protective is because it is an adherent oxide (the other reason being that aluminum oxide is such a stable compound). It is adherent because when it is converted to oxide, the volume doesn't change. Other oxides, such as the common hydrated iron oxide, grows. This is why you get rust scale on automotive iron that spalls off and isn't considered protective.

Strider, I still don't see where you disagree with me. It is commonly held that absolutely pure water will strip ions from unpassivated metal surfaces. Just the fact that you control the pH slightly acidic tells me you don't run pure water in your system. The water in itself does not passivate the metal. I believe you missed a step in your explanation. In fact, that is how one of my clients checks his product for proper passivation. After the passivation process and rinse, he rinses it in ultra high purity water (I believe he said one-millionth ohm water) and checks that the conductivity doesn't significantly increase.

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95 E320 Cabriolet, 169K

What does M-B use at the factory when they initially fill the radiator?

Best Regards,
Jim

Yeah, I missed a step that most people outside the nuclear industry never have to deal with, hydrolysis of the water by ionizing radiation. In the reactor, some water molecules are ionized or lysed due to the neutron field. These create OH- and H+ ions. For this reason, we have a hydrogen water system that injects hydrogen gas into the water. By driving the pH slightly negative and injecting H2, we hope to drive the reaction back, binding up the ions back into forming water molecules...(Le Chatliers principle or something like that? Its been oh, 15 years since I studied chemistry. I'm a mechanical engineer.)

The water is as pure as we can make it, in a system that runs around 548 degrees F, with two phase flow (water and steam), flowing through a reactor producing 3486 Megawatts of heat, with all types of dissimilar metals and galvanic reactions throughout, and other ions like boron from the control rod blades. Our biggest problems are with our condensor, which is made from admiralty brass and badly needs retubing. (We just keep plugging more and more tubes.) Actually, a condensor leak shut us down prematurely before our last refueling outage. The nuclear steam side is of course under vacuum in the condensor, and we use recirculated river water to cool the condensor. (The circ water goes to 6 mechanical draft cooling towers, dumping over 2000 megawatts of heat into the air.) The river water got sucked in through the leak and the conductivity detectors went off. Conductivity went above our license limits and we then had a controlled shutdown.

For us, protecting the passive layer isn't just a matter of chemistry though. The passive layer gets 'mechanically' removed due to the forces of the flow through the pipes too. (Erosion Corrosion, as well as cavitation in some spots). The bottom line though is this: After the steam lines to the turbine, the rest of the piping is called BOP, or Balance Of Plant. None of that stuff is 'Safety Related'. Our primary concern is in protecting the pressure vessel and its internals like the reactor recirc jet pumps. The BOP piping, feedwater heaters, etc can and does get replaced, but we only have one vessel, and it is a legal, credited, safety barrier.

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On the plains of hesitation bleach the bones of countless millions who at the dawn of victory, sat down to wait, and waiting -- died

Not different chemistry for the systems at my plant, a Boiling water reactor (BWR). We make the steam in the vessel, which then goes through a steam separator, then a steam drier, then out 4 main steam lines at 99.8 % quality to our high pressure turbine. We don't have a secondary loop with pressurizors and steam generators and all. We have had some problems with errosion / corrosion and 'tiger striping' in our BOP lines... when identified our usual course of action is to replace the carbon steel piping with stainless.

Yeah in PWRs (Pressurized Water Reactors for those that don't know), the chemistry is REALLY different in the reactor core. They finely control reactivity by adjusting the concentration of boron ions in the water (boron absorbs neutrons). That boron is added by adding boric acid. Using boric acid has some serious risks. I refer to the Davis Besse event.

In the BWR we finely control reactivity by adjusting the rate of water recirculation. The slower the recirculation, the more voids (bubbles) are formed on the fuel surfaces. Water is a good moderator for neutrons (slows them down into the thermal range, and thus propigates the reaction), while air is not. So the more air bubbles, the reactor power goes down. Increase the recirculation, the bubbles get swept away, and power increases.

Of course our chemistry is really strange these days. We recently added a hydrogen water chemistry system, injecting hydrogen gas into the water to bind up any free oxygen and thus try and prevent corrosion, such as intergranular stress corrosion cracking (IGSCC) in the vessel internals. During our upcoming refueling outage we are going to be injecting nobel metals in the water as well.

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On the plains of hesitation bleach the bones of countless millions who at the dawn of victory, sat down to wait, and waiting -- died

Tap water can be "hard" or heavily mineralized. This wll leave deposits in the cooling system. The water supply at my home in California is very hard. I started using Prestone Battery and Radiator water. You can find it in gallon jugs at your local PepBoys/AutoZone/McParts store. Basically purified, mineral free water. The cooling systems on both MB's are clean and free of scale after using this bottled water for a couple years.

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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

I always use distilled water.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Kestas is correct. (Distilled water by itself is bad.)I've used distilled water and MB coolant for 16 years and have had no problems.

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

i tend to use distilled water as in london,u.k. the water is of the hard variety.

Does anyone know what the dealer's use?

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

The MB dealers I Worked for all used TAP water and MB coolant
50/50 mix

MB says to NOT use distilled water. So, the dealers are doing exactly what is recommended by MB. I have used tap water in all my Mercedes including my 1966 230SL since new. All are fine with no deposits of any kind in the cooling system.