06

FEATURE ARTICLE

Do the RightThing:

M-B Anti-FreezeRecommendationsThose generics out there that

claim to meet most automakers'

specs aren't what the Stuttgart

engineers and chemists had in

mind when they designed the

cooling system

Water quality not only affects the rust/corro-sion inhibitors in some anti-freezes, but it maycontribute to electrolytic corrosion in the cool-ing system, which can produce deposits thataffect coolant flow and heat transfer. And if thewater is very hard, certain anti-freeze inhibitors-- particularly phosphates -- may react with thecalcium and magnesium (and even iron) inhard water to produce deposits that add to thecoolant flow and heat transfer problem. Seeaccompanying report: “When to Use Tap Waterin a Cooling System, and When Not To”.

Changing the anti-freeze/coolant in aMercedes-Benz vehicle, or even topping up thereservoir, is a straightforward procedure. Butpicking the right anti-freeze to use is not sostraightforward. There are many anti-freezes onthe market, and most are advertised as compat-ible with all others in all cars. StarTuned wouldlike to tell you why not to use just any anti-freeze in a Mercedes-Benz, even if it’s a rep-utable brand.

You may be thinking, “Mercedes-Benz is justtrying to sell its own approved anti-freeze. It’sjust another one of those not-invented-herethings.” Sorry, but that isn’t true, and we thinkwe can explain -- and hopefully convince you --to use either Mercedes-Benz's own anti-freeze,or only an aftermarket equivalent that meetsthe current Mercedes-Benz specification. Thisis particularly true today, when most of the anti-freeze aftermarket brands you’ll find are verydifferent in important respects.

First, let’s explain that because Mercedes-Benz vehicles are marketed worldwide, themanufacturer must make allowance for greatdifferences in water quality. The coolant in anengine normally is a 50-50 mixture of water andanti-freeze, and the water both improves heattransfer at high temperature, and lowers thetemperature at which the coolant will freeze.

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“Perfect together”: Mercedes-Benz anti-freeze coolantand distilled water in a 50-50 mixture in the coolingsystem. An aftermarket brand that meets theMercedes-Benz specification and/or deionized waterwill give the same good protection.

EG

PG

EG

PG

Boili

ng P

oin

t, D

egre

es

Centig

rade

Fre

ezi

ng P

oin

t, D

egre

es

Centig

rade

VOLUME % GLYCOL

30 40 50 60 70 80

30 40 50 60 70 80

118

116

114

112

110

108

106

104

102

0

–20

–40

–60

–80

BOILING POINTS AND FREEZING POINTSOF PG AND EG IN AQUEOUS SOLUTIONS

Charts show boiling and freeze points of anti-freezes in a 50-50 mixture with water. Notethat EG (ethylene glycol, the glycol used inmost anti-freeze) has a slightly higher boilingpoint and a slightly lower freeze point thanPG (propylene glycol). At concentrationsabove 70% anti-freeze, the freeze point of thecoolant actually starts to rise, so more anti-freeze is not better. The 50-50 mixture pro-vides the best combination of freeze andboilover protection, and good heater transferfrom the engine.

Mercedes-Benz anti-freeze is formulatedwithout phosphate inhibitors that producethese particular concerns about deposits. Doesthat mean you can use any anti-freeze withoutphosphates? You shouldn’t, even in areas with-out a hard water problem, because the factoryfill already has established a specific type ofrust/corrosion protection mechanism. A differ-ent type of rust/corrosion inhibitor package willnot continue with that form of protection andmight even cancel out protection.

Consider a situation in which the amount ofeach different inhibitor package is split, from

08

Anti-Freeze

use of two anti-freezes with different rust/cor-rosion protection mechanisms, so that each isunder 40% of the coolant (as low as 25% evenwith a 50-50 concentration). Neither inhibitorpackage may be strong enough to provide itsnormal type of protection.

Further, Mercedes-Benz is the only passen-ger car/SUV manufacturer to build into thecooling system a slow-release protectiondevice, that on some late-models permits a 15-year, 143,000 or 150,000 mile coolant replace-ment interval. The protection device -- a packetof silica gel in the coolant reservoir -- isdesigned to work with a Mercedes-Benz speci-fication coolant, and not others. And that's notjust a claim. We’ll be very specific. (Note: Thatnew service interval has not been extended toall models yet, and it should not be appliedretroactively to older models).

Fifteen years/143,000 or150,000 miles? Thatmust be one of those new anti-freezes you’veheard about, that are used in other manufactur-ers’ vehicles. No it isn’t. And despite anythingyou read about “compatibility,” these new anti-freezes are not approved for use in Mercedes-Benz vehicles, for specific technical reasons. Soyou understand the technical basis for these dif-ferent anti-freezes, a brief technical summaryof what they are follows.

But first, a couple of preliminary points:

All original equipment anti-freezes and mostaftermarket brands are about 93-95% ethyleneglycol, about 3-5% rust/corrosion inhibitors,plus about 2-3% water and/or solvent (requiredto keep the rust/corrosion inhibitors in solutionin the container and as the anti-freeze is pouredinto the system)—and a leak-trace dye.

A few aftermarket anti-freezes are made withpropylene glycol, which often is promoted as aless-toxic chemical, but which is not quite aseffective at freeze protection. So when an anti-freeze producer says his product is “compati-ble” with all original equipment anti-freezesand other aftermarket brands, he’s basing thison his own laboratory tests, which simply iden-tify a possible “battleground” issue. That is,when chemicals are “incompatible,” there isquick metal damage that shows up.

A refractometer provides the most consistent-ly accurate indicator of freeze protection of acoolant mixture, and should be used by a pro-fessional technician, instead of a hydrometeror test strip.

Excessive electrical activity in the coolant pro-duces electrolysis damage – corrosion thatrestricts coolant flow through the radiatorand heater core.

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However, “compatibility” doesn’t mean equalprotection. Even if an anti-freeze works well inone make of vehicles, it doesn’t mean it willwork well in all others, as we’ll explain whenwe talk about the different types of rust/corro-sion inhibitor packages.

You also should understand that the leak-trace dye simply identifies a leak. It does nottell you the type of anti-freeze. The most popu-lar anti-freeze colors are green (variousshades), yellow/gold, orange, blue, red andamber. In some cases, the colors were chosenby the anti-freeze producer to differentiate achange to a different formula, but not necessar-ily a specific one. In others, the color waspicked because it was considered unlikely to beconfused with fluid leakage from another com-ponent (washer fluid reservoir, transmission,power steering, etc.). Mercedes-Benz anti-freezepresently is dyed yellow/gold, but so are anti-freezes with totally different formulas andrust/corrosion protection mechanisms. The bot-tom line: ignore dye color.

Anti-freeze inhibitor packages are classifiedas “conventional,” and “extended life.” Theservice interval for “conventional” typically is2-3 years and/or about 24-40,000 miles. Todate, extended life may be “moderately extend-ed” (3-4 years) or five years or more, and up to150,000 miles. Mercedes-Benz, as noted withits 15-year/150,000-mile interval, has brokennew ground.

Rust/Corrosion Inhibitor Packages

You don’t have to be a chemist to understandthe rust/corrosion inhibitor packages. All youshould do is note the ingredients, see that theydiffer and realize why Mercedes-Benz anti-freeze protection mechanism truly is different,and the reasons why.

“Conventional green”: The inhibitors aresodium silicate and phosphate, both provenprotectors for aluminum, plus benzoate andborate (broad-range metal protection) and a “tri-azole,” one of a group of inhibitors that protectcopper-brass, plus an inhibitor that protectscast-iron.

“Japanese” green or red “conventional”: Ittypically contains phosphates and benzoate, atriazole; plus molybdate (cast-iron protection)and nitrate (a specific type of aluminum protec-tion). It contains no silicate.

Read the backs of these two containers ofcoolant. Note the Mercedes-Benz coolant con-tains forms of borate (sodium tetraborate)and benzoate (sodium benzoate) as well assilicates. The other anti-freeze contains onlyorganic acids (2-EHA and neo-decanoate).

Section of a Mercedes-Benz maintenancechart. Note that the “replace coolant” intervalis 15 years or approximately 143,000 miles.The mileage interval is as high as 150,000miles on some vehicles with the long-life rec-ommendation, based on the scheduled main-tenance interval.

WARNING: Contains ethylene glycol (107-21-1), diethylene glycol(111-46-6), sodium 2-ethyl hexanoate (19766-89-3), and sodiumneodecanoate (31548-27-3).PRECAUTIONARY MEASURES: Do not drink anti-freeze or solution.Do not beathe mist or vapors. Avoid prolinged exposure. Avoid skinand eye contact.FIRST AID TREATMENT: If swallowed, do NOT induce vomiting.IMMEDIATELY call a Poison Control Cnter or hospital emergencydepartment. If breathing is affected, move into fresh air. If in eyes,rinse thoroughly with water for 15 minutes. If on skin, remove con-taminated clothing and wash skin well with soap and water. If irrita-tion develops and persists, call a doctor.Ethylene glycol causes birth defects in laboratory amimals. Solution ispoisonous to animals.KEEP OUT OF REACH OF CHILDREN

It’s the Mercedes-Benz cooling system itself -- the metallurgy, the gasket materials, the flowpattern of the coolant plus the use of the silicagel packet -- that combine with the field experi-ence to assure that a particular anti-freeze isthe right choice.

The long-term validation of the Mercedescoolant in a Mercedes cooling system avoids theneed to deal with the concerns about OATcoolants. Why would you want to take a chancewith anything other than the Mercedes-Benzrecommended hybrid type? If you buy youranti-freeze from an aftermarket source, use areputable brand that meets current Mercedes-Benz formulation, typically labeled a G-05coolant. We bought Mercedes-Benz authorizedanti-freeze from a Mercedes-Benz dealer, andthe list price was only a dollar and change morethan the price of national brand anti-freezes inan auto parts store.

Note: some anti-freeze suppliers claim theirproducts meet specifications of all manufactur-ers, and provide a long list of manufacturers’specifications their products meet. However,over the years all vehicle makers have used anumber of different specifications, not all of

10

Anti-Freeze

Organic acid technology/extended lifecoolants (called “OATs”): Although benzoate isan organic acid, it is not used in an exclusivepackage with other organic acids in an OAT. Theorganic acids used in American anti-freezesinclude one 2-EHA, among others (such assebacate and neo-decanoate). They contain nosilicates and no phosphates. Japanese OAT anti-freezes do not use 2-EHA but they do containphosphate. Note: 2-EHA (2-ethylhexanoic acid)is a “plasticizer,” which means it softens plas-tics. Gaskets are made with plastic and therehave been laboratory tests reported by othermanufacturers, that raise concerns aboutcoolant-sealing gasket leakage with 2-EHA.

Mercedes-Benz type hybrid: Originallydeveloped to work well with both diesels andgasoline engines, this anti-freeze uses a low-sil-icate formula. It also contains benzoate andborate, plus benzo-triazole for copper-brass pro-tection, nitrate and nitrite (protects cast-ironliners in diesels). It was demonstrated to be arobust formula that would work for extendedintervals, and with Mercedes slow-release“refreshment” of the coolant, capable of longlife in a well-maintained system.

As these actual receipts show, you won't spend any more when you use the real thing.

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E-Class including CDI (diesel).

SLK Class (including new model with four-valve V-6)M-Class

S-Class (including V-12 bi-turbo) *

MERCEDES-BENZ MODELS WITH COOLANT REPLACEMENT INTERVAL OF 15 YEARS / 143,000 OR 150,000 MILES

* Three-year coolant replacement interval for the intercooler circuit of the bi-turbo

2004-2005

2005

C-Class SL ClassCLK Class

CL Class (including V-12 bi-turbo)*

2003-2005

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Anti-Freeze

them current. The list may not apply to the mod-els you’re working on, so be cautious.

Anti-freeze producers also may claim that ifyou drain the cooling system, you avoid any per-formance issues when you switch coolants.However, this is not necessarily true in aMercedes, where specific protection has beenestablished with silicate inhibitor and the sys-tem is designed for continued “refreshment”from the silica gel. Further, it is very difficult tocompletely drain the modern cooling system inall cars, although use of good coolant changingequipment should remove about 90%. So longas the new coolant is the same type as the old,there’s no question about its performance.

Why some ingredients and not others?

Both silicates and phosphates work veryquickly, and are very effective in protecting alu-minum, “painting” the cooling system surfaceswith an anti-corrosion coating. Silicates also areregarded as a harder coating, and not a problemin hard water, so they are the Mercedes-Benzchoice for primary protection.

The speed of protection is important. Notonly do silicates work quickly in new engines,but also to protect new parts that are installed,and in a situation called “water pump cavita-tion erosion-corrosion.” Under some operatingconditions (particularly high temperature,high-load), the coolant may form low-pressurebubbles as it’s drawn into the water pump, andthese bubbles collapse as they flow through

the pump chamber. The collapse occurs withexplosive force, chiseling and pockmarking thepump surfaces protected by the anti-freezeinhibitors. This eroding of the surfaces of thepump chamber exposes unprotected “baremetal,” which corrodes. The long-term effect:deterioration of water pump performance, lead-ing to overheating and in winter, to poor heat-ing performance from low coolant flow. That’swhy Mercedes and many other vehicle manu-facturers rely on silicates.

By contrast, OAT coolants may take 5,000miles to protect a metal surface. Although OATcoolant inhibitors are very long-lasting (hencetheir use in extended-life anti-freezes), theirslowness to protect is a problem when there iscavitation erosion in the water pump.

However, silicates are “used up” in providingprotection throughout the cooling system. Thisis not in itself a problem, so long as the “paint-ed” silicate protection is maintained. However,as noted, some silicates continue to be neededfor extended service, to perform such functionsas water pump internal “repair” protection.

Although most manufacturers have recog-nized silicates’ advantages, others were appre-hensive about using a high-silicate formula toget long-term protection from it. Mercedes-Benzhas been using the silica gel in a meshed-plas-tic container inside the coolant surge reservoirfor many years to gradually “refresh” the sili-cate content over a period of years.

You may be wondering about the use of silicagel, which is well-known as a desiccant (to

This coolant pump chamber was pockmarkedby cavitation erosion-corrosion, which wouldeventually reduce performance of the pump.

Seven times multiplication of the coolantpump surface clearly shows the pockmarkingthat leaves metal unprotected, and subject tocorrosion.

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absorb moisture) in many packaged goodsexposed to ambient humidity, and even in someolder automotive air conditioning systems.

However, in a coolant reservoir, it works dif-ferently, by absorbing enough coolant to estab-lish a “balance” and dissolve very slowly toreplace silicates used up to protect metal sur-faces in the cooling system. The silica gel pack-et gradually adds a very tiny amount of silicateinhibitor to the coolant over the years, reachinga “plateau” in the coolant.

You don’t have to replace the silica gel. In fact,laboratory tests show that even after manyyears, most of the inhibitor remains in the gel,still available to add protection. An anti-freezechemist described it as a “silicate trust fund.”Actually, the concept is somewhat similar to theuse of time-release additives in the coolant fil-ters of some “big rig” (Class 8) diesel engines.

Anti-freeze inhibitors have different metals toprotect, so the Mercedes-Benz formula is total-ly-balanced to protect them all. To be able to

extend the service interval from three years(still the service interval on some new modelsand all older ones), Mercedes has re-engineeredcomponents as required. That’s why the serviceinterval was increased so dramatically onlyafter both re-engineering of cooling systemcomponents and the long period of field andlaboratory experience with the silica gel“refreshment.”

Mercedes-Benz coolant service intervals

Mercedes-Benz with its hybrid coolant haslong been able to recommended a moderately-extended service intervals of three years, 50%longer than with conventional coolants. Aftercooling system re-engineering and testing,plus the rust/corrosion inhibitor refreshmentby the silica gel packet, the interval has beenextended to 15 years (143,000 or150,000miles, the variation based on the regular main-tenance schedule).

Section of a Mercedes-Benz maintenance chart for the SL. Notice that this one lists a three-yearcoolant replacement interval for 2003. The 15 year/150,000 mile interval only applies since 2004model year, as explained in the listing that follows.

Visit us at our new websitewww.MBWholesaleParts.com

to view this article and all past issues of StarTuned,along with a wealth of information on

Genuine Mercedes-Benz Parts.

14

Anti-Freeze

However, the new interval applies only to cer-tain late-models and should not be appliedretroactively to older ones.

Further, Mercedes-Benz continues to recom-mend that the coolant level be checked, andadjusted if necessary,: (using authorizedcoolant/water mixtures only) at each scheduledmaintenance service, which ranges from 10,000to 13,000 miles or once a year.

There’s also are special situations. One is the6.0-liter V-12 “bi-turbo” engine, which has asecond cooling system circuit (with an electriccoolant circulation pump) for the turbochargerintercooler. That circuit still carries a three-yearcoolant replacement, which should be per-formed as part of scheduled maintenance.Another is the 2005 SLR McLaren, which car-

ries a four-year coolant replacement interval.Although the following list of models sold in

the United States was drawn from theMercedes-Benz scheduled maintenance forms,you also can refer to the owner’s manual if youhave any doubt about the correct interval. Andif you use the Mercedes-Benz technical infor-mation website (www.startekinfo.com), you’llbe able to check service literature for anychanges.

Section of the Mercedes maintenance chart for the S-Class shows a three-year coolant replacementinterval for the “low-temperature circuit,” which is the turbocharger intercooler. The interval for S-Class engines is 15/150.

addition, if the water is veryhard, metallic particles maycontribute to electrolysis fail-ure of automotive heatexchangers. Virtually allcoolant is at least slightlyconduct ive . And i f youground a voltmeter and insertthe positive probe into thecoolant, you’ll find a smallvoltage--often under 0.1 V.Metallic particles in coolantadd to the current-carryingability of the coolant (equalshigher voltage that forcescurrent through the heaterand/or radiator to electricalground to complete the cir-

cuit). This electrical activity causes corrosion toform and the corrosive deposits may restricteither or both heat exchangers

How can you tell if the water is “soft” enoughfor use? A simple way is to look at householduse of water in your area. The water is hard iflaundry requires more than the minimumamount of detergent to clean clothes, if depositsbuild up in sinks, tubs and washing machines,and if household spray irons and coffee makersplug up and require frequent cleaning. Watertest kits are available, or ask a local distributorof water softening equipment to test for you.

Or you can pick up containers of distilled ordeionized water, sold in supermarkets. For wellunder $1 gallon, it’s an inexpensive item forwhich a customer should be willing to pay whenyou explain the advantage.

Distilled water has been boiled to a vapor,which then is condensed, so virtually all of thehardness grains are left in the boiler.

Deionized water (also called “demineralizedwater”) is softened water. The water is passedthrough a resin bed, in which the calcium andmagnesium ions are “exchanged” for sodium.Yes, the salt content of the water goes up a bit,but the water is even lower in content of thehardness grains than distilled water. So it’s suit-able for automotive use, too.

Less than 3.5 3.5 - 7 More than 7

Water Hardness(Concentrations in gpg)

When to UseTapWater in a Cooling System,andWhen NotTo

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Tap water, even if it’s good enough to drink, isnot necessarily good enough for a car’s coolingsystem. Hard water is the primary issue, andwater in the U.S. is generally hard. But whatdoes hard really mean and how hard is too hard?

Tap water that comes from underground wellsand aquifers may pick up mineral and metallicparticles, primarily calcium and magnesium,which are the key ingredients in “hardness.”Approximately 17 parts per million of these par-ticles are the starting point, and any numberover 120 ppm is considered somewhat hard.Most household “hard water” measurements arein grains – 17.1 ppm equals one grain, and 7grains is equal to 120 ppm.

In some areas the water hardness is as high as850 ppm – 50 grains. For automotive use, youwouldn’t want to use anything close to that. Infact, the best policy is to use only water 7 grains(120 ppm) or lower, and the lower the better.

Elsewhere in this report, StarTuned notesthat Mercedes anti-freeze avoids the use ofinhibitors that may cause special problems inhard water. However, don’t take that to meanthat using Mercedes anti-freeze prevents anyissue with hard water. It doesn’t. Hard waterstill is not good for any cooling systems,because the minerals and metals may result indeposits that could restrict heat exchangers. In