'98 E320 Coolant change--Distilled or tap water??

[johneb48]

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

[Kestas]

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".

[MikeTangas]

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.

[Ali Al-Chalabi]

I always use distilled water.

[PaulH]

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.

[sunil190e-1.8]

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

[blackmercedes]

Does anyone know what the dealer's use?

[mark cummins]

Originally posted by blackmercedes
Does anyone know what the dealer's use?

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

[pfphipps]

Originally posted by mark cummins
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.

[Kestas]

Pfphipps, where does MB say not to use distilled water? MB is actually casual yet pragmatic about the water used.

This is straight from the MB CD manual (20-0100):

"Use water which is clean and not too hard. Drinking water frequently, but not always, satisfies requirements. The content of dissolved substances in the water may be of significance for the occurrence of corrosion. If the water quality is not known, distilled or fully desalinated water should be used. For water quality see Mercedes-Benz Specifications for Service Products."

Interestingly, my booklet on Factory Approved Service Products (dated 11/01) does not address water quality, so the last statement is a link to nowhere.

But I'll agree that the dealers are doing exactly what is recommended by MB.

[d2bernhard]

I use filtered drinking water

[Duke2.6]

The "don't use distilled water statement" applies to running STRAIGHT distilled water. Guys actually used to do this way back when, but without corrosion inhibiuitors a few metal ions will dissolve from the metal surfaces in contact with the water and you have a battery! If the engine has dissimilar materials such as aluminum and cast iron, the aluminum will rapidly corrode.

When using ANTIFREEZE, it is best to use distilled water, so you don't introduce any additional salts in the system. Chlorine in particular is not good, however, most manufacturers say that "potable drinking water" is okay to mix with antifreeze.

Duke

[ericnguyen]

If you like chemistry, and want to know why the combination of Mercedes coolant (Zerex-G05) + Distilled water is best for your MB cars, you can read my posts in the 2 following threads:

http://www.peachparts.com/shopforum/showthread.php?threadid=85709&highlight=antifreeze

http://www.peachparts.com/shopforum/showthread.php?threadid=83661&highlight=antifreeze

Best regards,

Eric

[Strider]

Originally Posted by Kestas

Though some will point out that distilled water may start stripping metal ions from engine parts, mixed with coolant this phenomenon goes away.

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.

[benzfan]

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...