From Mon Jan 28 17:48:39 2002
Date: Mon, 28 Jan 2002 18:25:34 -0500
From: Skip Bogard <>
Subject: Re: [E36M3] BMW Antifreeze only?

"McCarthy, Brian" wrote:

> I'm preparing to change the water pump, thermostat & housing, radiator,
> timing chain tensioner, etc.

> In reading the procedures, most specify BMW antifreeze. Why would a BMW
> engine need a different antifreeze than what the rest of the other engines
> out there?
> Is there something special about BMW antifreeze?
> Can anyone make a recommendation of an "after market" antifreeze? (Seems
> like a strange concept - "After Market Antifreeze")

Brian, I give the following two articles to any

        friend who thinks they might run down to Pep Boys 
        and pick up the right jug of antifreeze for their 
        car.  I tell them to read these, and if they make it all
        the way to the end (or even if they don't) then the message 
        they should have received is: 

              "Run the anti-freeze that the manufacturer 
               has specified for the car..they have given this a 
               LOT more engineering thought than you ever have, and 
               picking anti-freeze is no longer trivial.

Brian, you should probably replace your radiator cap too,

but we can also say you covered that with your "etc".

Both articles were lifted from a ASE technician's website... Best,


The parts store now stocks three colors of antifreeze: yellow, green and orange. Huh? Isn't all antifreeze green? Isn't it all the same?

Bad News, Good News

The bad news is that it doesn't come down to color matching. Isn't all antifreeze compatible? Sorry, but it isn't. There are a few cases where you can get a fast case of corrosion, some where the water pump can be both eroded and corroded to an early death, and a lot of cases where you can shorten the effective life of the antifreeze. Antifreeze itself (most commonly a chemical called ethylene glycol) doesn't wear out–ever–but the key ingredients are the rust and corrosion inhibitors, and they get used up. The most common inhibitors, silicates for aluminum protection, are used up faster than others. That's why some new cars (all General Motors, Mercury Cougar, VW/Audi models) have red or orange antifreeze with a new class of inhibitors, called organic acids. Examples of U.S. brands with these organic acids: Havoline Dex-Cool and Prestone Extended Life, both recommended for five years or 150,000 miles. That's the good news.

Fill 'Er Up

How about just pouring orange antifreeze into every cooling system, say, yours? Sorry, but it's not that simple. The new organic acid antifreezes may be used only if the cooling system has an aluminum radiator (rather than copper-and-brass).

However, let's assume the reason you're thinking of a coolant change is because you're changing a cooling system part (pump, radiator, heater, thermostat housing) on a system with a conventional coolant, not an organic acid orange or pink. In that case, don't change to organic acid orange, even if the part you're installing is aluminum. Use a fresh fill of familiar U.S. yellow/gold or green silicated antifreeze.

The two orange extended-life antifreezes are compatible with each other, with what's factory-fill in GM cars and the '99 Mercury Cougar, and with the pink in VW/Audi cars. However, they're not compatible with a special orange antifreeze in 1998-99 Chrysler L/H cars (Dodge Intrepid/Chrysler Concorde and 300M), a special "hybrid" mix of organic acids and silicates. The green in most Japanese cars contains no silicates, so it's not the same as the green in the parts store. The yellow in some European cars contains some silicates, but it's very different from yellow Prestone, the top-selling U.S. brand. And then there is red antifreeze used by Toyota, and blue used on some European and Korean cars.

Freshen Up That Cup For You, Sir?

What about just topping up a system that's low? What kind should you use? If the system (except for Chrysler L/H) has orange or pink, use Prestone or Havoline orange for top-up. All you have on hand is regular U.S. yellow/gold or green? Well, if you're desperate, use what you've got, because it's better than running low on coolant and possibly overheating. But the mixture is shortening the life of the antifreeze. By how much? It would take lab tests to tell, so the best deal is to do the equivalent of a "retrofit." Can you retrofit all systems? Sorry, the answer is no. What about draining green or yellow/gold from the radiator and refilling with orange? Is that considered a "retrofit"? No, and you'd better not try that, either.

What if the system has Japanese green, Toyota red, Korean or European blue, or European yellow? As we noted, European and Korean formulas have silicates, so U.S. green or yellow/gold is all right, but it slightly compromises the extended life formulas some have. Typically all that means is: Change at 30,000 instead of 36,000 miles. The Japanese green and red antifreezes have no silicates, but they are very different from U.S. orange. If you really drain out the old antifreeze from any of these systems (thoroughly rinse the system with fresh water), you certainly can refill with a U.S. yellow/gold or green silicated antifreeze.

Now let's look at "retrofit" and "drain and fill" and explain what you can and can't do safely, and a bit of why. If a vehicle has a copper-and-brass radiator, forget a retrofit, says General Motors, because the organic acid (orange) antifreeze may not provide adequate protection for the lead solder in that radiator. The Chrysler orange hybrid combination of silicates and organic acids is meant to provide special protection for the water pump. Sorry, you can buy it only at a Chrysler-brand dealer.

Prestone believes you can retrofit to its organic acid orange almost any vehicle with an aluminum radiator and cooling system that has been well-maintained and is in good condition, if you do it right. However, the antifreeze maker recognizes the possibility of a problem with Dodge truck 5.9-liter V8 water pumps, for which green or yellow/gold U.S. antifreeze is recommended–if you don't get Chrysler's specific orange.


New Coolant Chemistry, Larry Carley, Underhood Service, June 2000

Cooling chemistry has undergone some significant changes in recent years. The familiar green antifreeze that has long been used in most vehicles is being replaced with a spectrum of not-so-familiar antifreezes in new cars and light trucks that range in color from red to orange to pink to blue. When you open a radiator cap today, you’re never quite sure what you’re going to find. But from a service standpoint, it’s essential to know what type of antifreeze is in the system so you can add a compatible coolant, or replace it with one that provides equivalent or better protection.

Let’s start with a look at the basic ingredients in antifreeze before we get to the various additive packages that make them different.

Ethylene Glycol
Ethylene glycol (EG) has been the main ingredient in almost all automotive antifreezes for many years, and will continue to be for the foreseeable future. Straight ethylene glycol freezes at about 8° F, boils at 330° F, and carries heat about 15% less efficiently than water. But when mixed in equal parts with water, it creates a coolant well suited to year-round driving.

The recommended 50/50 mixture of EG and water provides freezing protection down to -34° F and boilover protection to 265° F in a radiator with a 15 psi cap. If the proportion of antifreeze to water is increased to 70% EG and 30% water, the freezing point drops to -84° F and the boiling temperature goes up to 276° F. Mixtures greater than 70/30 are not recommended because the coolant’s ability to carry heat declines as the proportion of antifreeze increases.

Straight EG antifreeze should never be used in an engine because it may allow the engine to overheat. Likewise, straight water should never be used because it provides no freezing, boiling or corrosion protection.

Propylene Glycol
Another base ingredient that is used in place of EG in some aftermarket antifreezes (Prestone "LowTox" and Safe Brands "Sierra" antifreeze) today is propylene glycol (PG). The coolant’s thermal characteristics are similar to those for EG: a 50/50 mixture of PG and water provides freezing protection down to -26° and boilover protection to 256°. If the coolant mixture is increased to 60/40, freezing protection goes down to -54°F. The main advantage of PG compared to EG, however, is that it is considered "nontoxic" to animals. That doesn’t mean it is "safe" to drink, but it greatly reduces the risk of poisoning a pet.

Pure PG boils at 370° F and provides freezing protection down to -70° F, so it is sometimes used straight without any water at all as a coolant in racing applications. Running PG straight provides better cooling because there is no water to vaporize in hot areas of the cylinder head. This also allows the use of very low pressure or even no pressure cooling systems.

PG and EG are both compatible antifreezes and can be intermixed without affecting cooling performance. But intermixing the two different antifreezes is not recommended because doing so defeats the reduced toxicity advantages of PG. Also, if a vehicle’s cooling system is filled with an extended-life EG coolant, adding PG (which is not currently formulated for extended service) will reduce the service life of the coolant mixture to that of a conventional green coolant.

Intermixing PG and EG antifreeze also makes it impossible to get an accurate indication of the coolant’s strength if you’re using a hydrometer to check coolant concentration. The specific gravity of EG and PG are different, so a mixture of the two will usually indicate a lower freezing point than the coolant actually provides.

The best way to determine the concentration of PG in uncontaminated coolant (no EG present) is to use a refractometer; the specific gravity of PG increases up to about a 70% concentration, then falls off. Consequently, a 100% PG solution will read the same as a 45% solution on a hydrometer.

PG is approved as an acceptable replacement coolant by General Motors and others, but if making a change, it’s important to remove all of the old EG coolant before adding PG to the system.

Corrosion Inhibitors
Because coolant is in constant contact with the metal parts of the engine and radiator, some type of corrosion inhibitors must be used in the antifreeze to protect all metal surfaces from electrolysis. That includes cast iron, steel, aluminum, brass, copper and lead solder.

Most conventional antifreezes formulated for the North American market, whether green or yellow in color, contain inorganic salts of borate, phosphate and silicate to prevent rust and corrosion. The additives create an alkaline coolant mixture that typically tests at about 10.5 on a pH scale. The silicates form a protective coating on metal surfaces and are especially good at protecting aluminum.

To ensure that the coolant remains alkaline for a reasonable length of time, there must be enough corrosion inhibitor to neutralize the acids formed from glycol degradation that occur over time. This neutralizing capability is called "reserve alkalinity," and it varies depending on the type and quantity of additives used in a particular brand of antifreeze.

Heat, dissolved oxygen, minerals in the water and corrosion inhibitor reactions at the metal surface gradually "use up" the corrosion inhibitors, and, once depleted, the coolant becomes acidic and corrosion accelerates. The secret to preventing internal corrosion, therefore, is to change the coolant before all the reserve alkalinity has been used up.

Periodic coolant changes are especially important with today’s bimetal engines and aluminum radiators and heater cores because the different metals create a miniature battery cell that promotes electrolytic corrosion. Aluminum becomes the sacrificial anode, iron the cathode, with the coolant serving as the charge-carrying electrolyte. The higher the percentage of dissolved minerals and salts in the coolant, the better it conducts electricity and the faster the aluminum is eaten away. As long as the corrosion inhibitors are working, the process is held in check. But once they’re used up, corrosion starts to eat away. The most vulnerable components are usually the thinnest, which include the radiator and heater core.

Other problems can also accelerate the breakdown of the coolant. An exhaust leak into the cooling system through a cracked head or leaky gasket will quickly destroy reserve alkalinity in the coolant because oxygen reacts with the additives in the antifreeze. If an engine has a leaky head gasket, don’t reuse the old antifreeze when the gasket is replaced.

The amount of additive needed to protect the cooling system isn’t much, only about 2-3% of the total liquid in the jug. This is usually enough to protect for at least two years or 30,000 miles in most vehicle applications - or even longer if the antifreeze is mixed with relatively pure water (distilled or deionized). Some say ordinary antifreeze can go as long as five years or 100,000 miles before the corrosion inhibitors are fully depleted - provided pure water is used to fill the system, the cooling system was relatively clean when filled (no accumulated rust or scale), and the coolant level is kept full (no air entrapment).

Hard water that contains high amounts of calcium and magnesium can react with phosphates in the additive package to form sediment and scale. That’s why the European vehicle manufacturers use antifreezes that contain no phosphates (hard water is common in Europe). European antifreeze may be dyed blue, yellow (Mercedes) or pink (VW and Audi). Tap water in North America also contains calcium, but isn’t as hard as European tap water so phosphates are considered okay to use here.

Under no circumstances should "softened" water be used in a cooling system because softened water substitutes sodium (salt) for calcium. Sodium is very corrosive to all metal surfaces and undermines the corrosion-inhibiting abilities of the additives.

The Japanese and other Asian vehicle manufacturers, by comparison, prefer an additive package that contains phosphates and other inhibitors but no or low silicates. Japanese coolants may be dyed red, but some of the newer blends are dyed green.

According to the aftermarket antifreeze suppliers we interviewed, using a typical green antifreeze formulated for North American domestic vehicles in European or Japanese vehicles should cause no problems. The basic metallurgy is the same so the degree of protection provided should be the same: two years or 30,000 miles.

OAT Technology
The latest corrosion-inhibiting additives are based on a different chemistry called "Organic Acid Technology" (OAT). Antifreezes with OAT corrosion inhibitors contain organic acid salts of mono- and dicarboxylic acids such as sebasic and octanoic acids, plus tolytriazole. The coolant is less alkaline and protects with a pH reading of only about 8.3. Brands with the OAT additive package include Texaco/Havoline’s "Dex-Cool" and Prestone’s "Extended Life 5/150" antifreeze. OAT coolants contain orange dye to distinguish them from other coolants with conventional additive packages.

The main advantage of OAT technology is extended service life: up to five years or 150,000 miles. But to achieve this length of service, the OAT coolant must not be intermixed with any other type of antifreeze. If the system is topped off with ordinary green antifreeze, the corrosion protection will be reduced to that of a conventional coolant, say the coolant manufacturers.

General Motors was the first domestic vehicle manufacturer to make the switch to OAT coolants, starting in 1995. Since 1996, all new GM cars and light trucks have been factory-filled with orange Dex-Cool coolant. GM says Dex-Cool can be used in older vehicles provided the cooling system is first flushed to remove all traces of conventional coolant. But people have said OAT-based coolants do not provide adequate protection for vehicles with lead-soldered copper/brass radiators - a charge the makers of OAT antifreeze say is not true. Texaco/Havoline and Prestone both say their products meet or exceed the ASTM D-2570 standards for corrosion protection.

There has been some controversy regarding the use of OAT coolants because of sludging problems GM experienced in some 4.3L S10 truck engines. GM service bulletin #99-06-02-012 says the sludging problem is caused by air pockets in the cooling system from failing to maintain the coolant level or not getting all the air out the system when refilling the cooling system. GM’s fix for the condition is not to switch back to a conventional coolant (which some people advocate), but to flush the system repeatedly until all the brown sludge has been removed. The system can then be refilled a 50/50 mix of Dex-Cool and clean water.

Despite the problems with the 4.3L truck application, the use of OAT antifreeze is expected to grow. DaimlerChrysler introduced its own extended-service OAT hybrid coolant for passenger cars in 1998. Unlike Dex-Cool, the DaimlerChrysler coolant contains silicates for extra aluminum protection. DaimlerChrysler, however, does not recommend using their OAT hybrid coolant in older vehicles.

Ford in North America is still using conventional additives in its antifreeze, with the exception of the ’99 and up Mercury Cougar, which now uses an OAT coolant. But Ford of Europe has switched over to OAT antifreeze for many of its vehicles. OAT has also been approved by truck manufacturers including Navistar, MAC and Caterpillar.

Coolant Checks
One problem we have in the aftermarket is that we have no way of knowing what kind of antifreeze is in a customer’s cooling system when it comes into the shop. It may be the factory-fill coolant, it may be an aftermarket coolant, it might be a propylene glycol coolant, or it might be a mixture of several different types of coolants. If you don’t keep this in mind, a simple coolant check with a hydrometer may give you a false indication of the strength of the coolant. A refractometer is a better tool to use because it doesn’t measure specific gravity but how the liquid bends light.

Chemical test strips are available to check both the concentration and condition of the coolant, too. But test strips designed for conventional green coolants won’t give an accurate indication of the coolant’s condition if used with an OAT type of coolant.

A special test kit marketed by Analyst Inc. (877-839-2435) can give a pass/fail indication if a vehicle with Dex-Cool coolant has been contaminated by another type of coolant. If it contains 15% or more of something else, it fails the test. The kit (P/N LS-TST-STRIP) sells for $24.99 and includes 10 test strips.

Coolant Service
Though most coolant service consists of flush and fill, ethylene glycol coolants can also be recycled using the proper equipment (see October 1999, Underhood Service). Recycling has obvious environmental benefits, and can be a source of additional profits for your shop. EG coolants with OAT additives can also be recycled, but the aftermarket additives currently available only return the coolant to a standard two-year/30,000 mile silicated coolant.

When refilling a late model GM vehicle that was factory-filled with Dex-Cool, you have to decide what type of coolant to use. According to GM, Dex-Cool is the only acceptable coolant. But once the vehicle is out of warranty, there’s no reason why you can’t use another brand of OAT coolant or a conventional EG or PG coolant, say the makers of these products.

The same goes for using an OAT coolant in an older vehicle that contains a conventional green type of coolant. If the system is thoroughly flushed, you can give your customer the extended service benefits that an OAT coolant provides. OAT coolants can also be used to refill European and Asia vehicles, provided the system is first flushed to remove all traces of the old coolant.

The National Automobile Radiator Service Association (NARSA), however, is more cautious about the use of OAT coolants. NARSA says OAT coolant should not be used in any Ford product (except the ’99 Cougar) or Chrysler because there is a risk of water pump cavitation erosion. GM reportedly redesigned its water pumps to eliminate cavitation erosion.

Another question that comes up is one concerning the compatibility of Dex-Cool with other OAT coolants. Texaco/Havoline, the manufacturer of Dex-Cool, says their additive package is not the same as one in Prestone, and that other brands do not meet GM’s Dex-Cool GM-62277M requirements. Prestone, on the other hand, insists their Extended Life 5/150 OAT-based product is compatible with Dex-Cool and meets the GM-62277M requirements. Go figure.

Regardless of what type of coolant is used to refill a cooling system, the system should be cleaned if sediment, rust or scale are present. Also, the system should be pressure tested to make sure there are no leaks. And don’t forget to pressure test the radiator cap, and inspect the belts and hoses, too.

Refilling some of today’s vehicles can be tricky if the heater core or other hoses are higher than the radiator cap. If the system has bleeder valves, use them. If it doesn’t it may be necessary to jack up the front of the vehicle so the radiator cap is the highest point in the system.

Keeping Coolant Clean

A survey of ASE-certified automotive technicians throughout the nation determined that coolant is the second most neglected vehicle maintenance item. Coolant should be checked for both strength and also pH level at each service. To check the pH level, you should use a chemically treated test strip, which can be purchased at most parts stores.

The average pH level range of typical coolant is around 10.5. When diluted with water, it drops to 8.5 to 9. A pH level at 7 or lower can lead to both excessive corrosion and electrostatic discharge (ESD). With ESD, the PCM can receive false readings from the electronic coolant temperature sensor, which can lead to poor fuel economy and the setting off of diagnostic trouble codes. With a low pH level, the coolant becomes acidic, which can cause hose, radiator and water pump failures.

So the bottom line is that if coolant is contaminated or the additives are depleted, flush the system. The use of low or no silicate coolant at a 50/50 ratio is best. You and your customer will be satisfied with a job well done.

Also, radiator caps play an important role on automotive cooling systems. They can lead to radiator or water pump seal damage. The job of the cap is to hold pressure on the system, which raises the boiling point of the coolant and prevents steam bubbles from forming inside the cooling system.

Caps should be pressure tested each time the system is serviced. Most caps will range from 4 psi to 18 psi.

When testing the cap, it should hold pressure for two minutes. If it doesn’t, the cap should be replaced. The condition of the gasket in the cap also should be inspected for swelling or tears that could lead to coolant loss and engine overheating.

Courtesy Airtex Automotive Division

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