Some say to use MB coolant and distilled water; others say that distilled water creates too much "ionic activity". Would appreciate what folks who do this for a living think. Thanks for your time.

Mike Murrell

First let me qualify this by saying I am no longer a profesional mechanic. Unless you have something drastically wrong with your tap water, use it, I can just about guarrantee MB does not use deionized water. Use a coolant that is campatible with aluminum.

FYI. In the old days of open cell batteries, deionized water was used for batteries so you can determine their charge by using a hydrometer which reads specific gravity. In an emergency, tap water could be used without harming the cells, but it would through off any future hydrometer readings.

I also just got sucked into paying $15.00 for 0.75 liters of DOT 4 brake fluid at MB, for which you will see a more detailed post shortly. Discount parts stores sell the same stuff for $4.50. MB engineers spend their time designing mechanical systems, not designing fluids (although they obviously are very proud of their brake fluid packaging). Save your money to buy OEM parts (brakes, hoses, etc) rather than over the counter fluids.

I will gladly retract these comments if one of the pro's corrects them, but I will be surprised if that happens.

Regards,

------------------
Deezel
87 300TDT
150,000 miles

Ions. Ions are what carry the charge in an electrolytic solution. Using distilled water removes ions and thus would be a benefit. But! Most european cars have requirements for phosphate free coolants. The reason behnd this is the amount of ions in the water most Europeans have for their cars. It is claimed that this is not necessary for most US water systems. Their level of ions is sufficiently low.

As to electrolytic mixtures, this is what we are trying to avoid. The key to this electrolytic mixture is that water is the solvent. Water supports electrolysis through its chemical nature. Antifreese is not an electrolytic solvent. The key is which is dissolved in which. The solvent is the medium. If you have water dissolved in antifreese it forms a non electrolytic solution. If the water is the solvent with antifreese disolved in it then you have an electrolytic solution. The key is the mixture. Make sure you have more than 50% antifreese and alls well.

As to brake fluid we use Castrol LMA Dot4 brake fluid but I wouldn't hesitate to use any reputable Dot4.


------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Deezel/Steve...thanks for elaborating on the "ion" issue...regards...Mike Murrell

Steve,

Regarding your discussion, are you referring to distilled water (as in the type you buy at the grocery store) or deinozed distilled water (that you can sometimes find)? It's been years since my chemistry days, but one of them is like acid. It will dissolve glass or metal containers. That's the one we should avoid. Do you recall which one? Also, your discussion makes some assumptions about the two solutions being equal in ionization and deionization. If memory serves, that is not necessarily so, but I can still be educated.

For what its worth to anyone reading this. I've been running 40/60 (antifreeze/distilled water) for almost 20 years in my Volvo, with changes every three years to the fluid. Still looks very clean for its age and almost no mineral deposits. main reason was I lived in West Texas, home of hard water, and I just kept the habit after I left.

PS, Mercedes and Preston's (5yr coolant) are great stuff. I especially like the residue it leaves if there is a leak. It helped me spot an earlier leak in my G. Preston advertises no phosphates and has the same color as Mercedes, but ????

Thanks.

JR, I can assure you that neither deionized or distilled water will dissolve glass or metal containers. They are both just very very pure forms of water, purified in by different techniques. Distilled water is purified by boiling and recondensing it, deionized water goes through a "deionizer". I drank deionized water for several years with no ill effects.

------------------
Robert W. Roe
1984 300SD 169K mi

I'm a little east of west Texas, but share the same problem...hard water. Alot of auto techs here say to use 50% coolant/50% distilled H2O. I have 2 Japanese vehicles that collectively have 550,000 mi. on them following the afore-mentioned regimen. I DO realize these are not German cars; nonetheless, their cooling systems are quite similar. Still stumped about the distilled water issue and wonderin' why my '83 Toyota truck with just south of 300,000 miles still has the same engine, radiator, etc., all courtesy of Prestone and distilled water. I do premix for what it's worth.

Regards...Mike Murrell

Deionized water has no calcium or magnesium in it. If you racall in the 60's radiators would collect white residue. This usually was the calcium and magnesium deposits. Oddly they are deposited more readily at higher temperatures. Corrosion is the reaction of oxygen with metals. In today's radiators with cooant resevoirs the oxygen is most likely boiled off and vented so it can't be a bad actor.

I have used deionized water and antifreeze in my vehicles since 1983 without the first problem. (Total of 500,000+ miles)

------------------
1991 350 SDL
114,000 miles

Bob, My description of "dissolving" was probably to strong. Etching would be a more appropriate term. I few years ago I was part of the world's largest aviation R&D facility. I met a few chemists (mad scientists) there and got a quick lesson on what happens when you leave a particular form of distilled water in a glass container. over time (a long time) it etches the glass. Mind you, we had our own distiller and then it went through a process to generate the two forms. Thought you'd be curious.

Cheers.

Chris:

You had found it odd that calcium deposits form more quickly under higher temperatures. Actually, this is not odd at all, since when calcium is present in hard water, and when the water evaporates, it leaves behind the calcium. And since water evaporates quicker at higher temperatures (boiling being the highest temperature that water can reach, when it is not under pressure), the water will evaporate faster.

Thus the Laws of Physics have again been proven immutable.......Andras

Andras - actually the solubility curve for these elements is the opposite of most other compounds. Without eveaporation the higher the temperature the less soluble the element is in water solutions. Ask any Chemist.

------------------
1991 350 SDL
114,000 miles

Chris:

Thanks, as I am not a chemist, I had no idea on the solubility, but my observation was that when water evaporates, it does leave the residue of minerals sittingbehind.

So I guess the Laws are still right - with the higher temperatures, the minerals are less soluble, and thus more likely to precipitate out, and when the water evaporates, it leaves the residue.

Whew, I'm glad I got all that straight in my own mind, and I now know where those deposits are coming from.

This also tells me that some sort or distilled or deionized or "softened" water is still the best in batteries, in cooling systems, and even in your own home's hot water heater (and as I am an architect, I know that be a real fact )....Andras

For the truly geeky...

There are quite a few different grades of Deionized or DI water. The one that is like an acid is ultrapure or electronics grade DI water. With a resistivity of 18Megohms and a ton of specifications as to total organic and dissolved solids, this stuff is indeed, very aggressive. This is due to its polar nature. Ultrapure water acts like an acid in quite a few environments. The piping for ultrapure has to be made from a special grade of Teflon Resin-PFA HP, either 340,350,440,or 450. Other materials generally considered to be corrosion resistant like PVDF (kynar) or ECTFE, are attacked aggressively by ultrapure water. Analysis of these materials after exposure yields results similar to exposure to highly concentrated sulfuric acid. 316 Stainless Steel suffers as well. It is generally considered unacceptable for use with ultrapure water due to the ability of ultrapure water to leach impurities out of the bulk matrix, thereby contaminating the water. Not good for semiconductor applications where limits for these ions is in the ppb. Under certain conditions, however, ultrapure water will reduce the passive oxidation layer and begin to corrode the bulk material. Localized boiling is one of these conditions. The mechanism here is the same for aluminum and mild steel as well. The boiling caused water hanmmer at the vapor nucleation sites. This breaks up the oxidation layer exposing the raw 316 stainless steel underneath. Normal corrosion proceeds as usual. Ultrapure water cannot exist outside of very carefully controlled conditions. Exposure to air quiclky drops its resistivity from 18 megohms to around 8 due to the saturation of CO2 in solution. I don't think anybody drinks this stuff or has it lying around. Normal Deionized or DI water has much lower organic and dissolved solids specs and measures out at around 1Megohm max. There are enough ions in solution here to tie up a lot of the polar water molecules, greatly reducing its aggressiveness. Aluminum has a wonderfully passive oxide layer that is impervious to just about everything. Under static conditions, that is. Moving fluids change everything. So does boiling and cavitation. Thus, susceptible components for corrosion would be water pumps, heads, radiators. Radiators are susceptible due to the highly tortured path that the coolant takes through it. This flow can strip the passive layer and expose the base aluminum, which corrodes quickly. There are a ton of corrosion mechanisms at work in any engine, (only the truly super-geeky need read the list at the bottom of the page...) The key is to minimize the effects by tying up those ions which cause the most damage. Chlorides kill. Phospates precipitate out and foul heat transfer surfaces. I'll save the full list for another episode of the dull-and-truly-geeky. The bottom line is that distilled or low grade deionized water will very likely reduce corrosion in your engines. Could've just said that first, I guess....

Val

Proceed only if thou art desperately in need of a life...
Forms of Corrosion
General/Uniform Corrosion:
Corrosive attack dominated by uniform thinning due to even regular loss of metal from the corrosion surface Atmospheric corrosion or degradation of material exposed to the air and its pollutants rather than immersed in a liquid
Galvanic corrosion that occurs when a metal or alloy is electrically coupled to another metal or conducting nonmetal in the same electrolyte
Stray-current caused by an externally induced electrical current
General biological corrosion of metals generally over the entire exposed surface in aqueous environments
High-temperature Oxidation corrosion by direct reaction of exposed metals to oxidizing agents at elevated temperatures
Other forms
Localized Corrosion:
all or most of the metal loss occurs at discrete areas
Filiform occurs on metallic surfaces coated with thin organic film, typically .1 mm thick, characterized by the appearance of fine filaments in semi-random directions from one or more sources
Crevice corrosion in narrow openings or spaces in metal to metal or non-metal to metal component sites
Pitting extremely localized corrosion marked by the development of pits
Localized microbiological cases where biological organisms are the sole cause or an accelerating factor in the localized corrosion
Metallurgically influenced corrosion: form of attack where metallury plays a significant role
Intergranular occurs when the corrosion rate of the grain boundary areas of an alloy exceeds that of the grain interiors
Dealloying a form of corrosion characterized by the preferential removal of one constituent of an alloy leaving behind an altered residual structure
Mechanically assisted degradation:
form of attack where velocity, abrasion, hydrodynamics etc. play a major role
Erosion removal of surface material by the action of numerous individual impacts of solid or liquid particles
Fretting combined wear and corrosion between contacting surfaces when motion between the surfaces is restricted to very small amplitude oscillations
Cavitation & Water drop impingement occurs on a metal surface in contact with a liquid, pressure differentials generate gas or vapor bubbles which upon encountering high-pressure zones, collapse and cause explosive shocks to the surface
Fatigue occurs in metals as a result of the combined action of a cyclic stress and a corrosive environment
Environmentally induced cracking:
forms of cracking that are produced in the presence of stress
Stress cracking service failures in engineering materials that occur by slow environmentally induced crack propagation
Hydrogen damage results from the combined action of hydrogen and residual or tensile stress

Val, Thanks alot. I love this web site.

Cheers,

My wife, a chemist, actually sat down and read a mercedesshop post with me today.

Whoa.

Thanks Val.

-Nick