Rick's Free Auto Repair Advice

Universal coolant?

Is it OK to use universal coolant?

No. Several coolant manufacturers claim their coolant works in all makes and all models. In other words, they want you to think their product is a universal coolant/antifreeze. I’ve got news for you; there’s no such thing. There CANT be because the metal alloys, plastics and seals are different in every engine. There are many different types of coolant and each one has a different type of anti-corrosion additive. Some are good for aluminum alloys while others are best for cast iron. Still others will work with plastics while some will soften and destroy plastics.

To qualify for the “all makes, all models” universal coolant moniker, manufacturers must include a dash of every type of corrosion inhibitor available, and many of those inhibitors are incompatible with each other and the materials used in your particular engine. Or, they remove certain types of additives that are essential for preventing corrosion in certain engines but can cause interaction problems when used with other coolants.

What’s in antifreeze coolant?

Most manufacturer-specific antifreeze coolant formulas use an 85-95% concentration of Polyethylene Glycol as the base chemical. Polyethylene Glycol prevents freezing and overheating, but doesn’t provide any corrosion protection. Corrosion protection inhibitor additives are what makes up the other 5 to 15% of the mix.

Corrosion inhibitors protect against metal corrosion, galvanic action and cavitation erosion and the inhibitors used must also be compatible with rubber and plastic seals, gaskets and fittings.

What’s the difference between antifreeze and coolant? See this post

There are two types of antifreeze corrosion inhibitors — Inorganic and organic

Inorganic Additive Technology (IAT) green coolant

The old green IAT coolant is based on ethylene glycol or polypropylene glycol with corrosion inhibitors like silicates, sodium or potassium salts of inorganic anions like: Phosphate, borate, nitrite, and nitrate. A given coolant formula contains varying amounts of two or more of these chemicals. The formula usually contains an azole compound like tolyltriazole, benzotriazole, or mercaptobenzothiazole as a copper corrosion inhibitor.

Silicate and phosphate corrosion inhibitors are fast acting so they work quickly to coat and protect bare iron and aluminum surfaces. These corrosion inhibitors are proven effective and are generally trouble free. The silicates form a protective barrier on everything in the cooling system, including rubber components. However, silicates wear out quickly. In fact, they can drop to less than 20% in just 10,000 miles.

That’s why traditional “greeen” coolants have a short life of just two year and less than 30,000 miles.Worse yet, silicates can precipitate out of solution to form deposits. If the deposits settle in seal areas, their abrasive qualities can cause premature seal wear and leaking. In an older vehicle that uses a heater control valve that regulates coolant flow to the heater core to adjust heater core heat output, the problem can be even worse. During summer operation when the heater control valve is closed, the silicates left in the heater core can form gummy deposits that clog the heater core tubes.

Phosphate is an anodic inorganic corrosion inhibitor that works well to protect aluminum and cast iron components from corrosion. Phosphate acts as a pH buffer and is often used by Japanese car makers. However, phosphates react poorly with hard water and can form scale in the cooling system which can plug up the radiator and heater core.

image of antifreeze adding to radiator

Typical green silicate antifreeze

Then why use silicate coolants?

Because they work really well to protect iron blocks and aluminum cylinder head engines. It reacts with cooling system metals to form a protective anode film that is literally adsorbed into the metal to “passivate” it. It works because it is an ANODIC inhibitor. As soon as the anodic film layer becomes higher than the cathode current density, the metal components are “passivated.” The silicate film is insoluble and impermeable.

The downside of silicate is that it has a short life so you have to flush it and refill about every two years. Silicate antifreeze is also prone to gelling. The worst part is that silicate is abrasive and damages water pump seals.

Silicate formulas are often used in European cars

Nitrates components to form a Nitrosamine passivation film. But nitrates have a short life and don’t work well on aluminum or aluminum alloys.

Borate is also an anodic corrosion inhibitors that works best with cast iron engine parts, but is corrosive to aluminum and aluminum alloys

However, it’s important to understand that anodic corrosion inhibitor concentration must be high enough to reach the passivation threshold to protect engine and cooling system metals. Many all makes, all models universal antifreeze formulas don’t contain high enough silicate levels to reach that point. An antifreeze with too low a concentration of anodic corrosion inhibitor is worse than having no anodic inhibitor at all. That results in an anode film that’s too thin to provide passivity, resulting in pitting and accelerated corrosion.

What is Organic Acid Coolant Technology?

Organic Acid coolant works differently than silicate/phosphate coolant. Cathodic corrosion inhibitors prevent the cathodic reaction with the metal components. To achieve this, the antifreeze contains metal ions that precipitate on cathodic metal within the engine and cooling system, forming an adherent film. Some examples of inorganic cathodic inhibitors are the ions of magnesium, zinc, and nickel.

Types of organic acid coolants

Organic Acid Technology OAT— no silicates. Often contain 2-EHA and /or Sebacate for corrosion protection

Hybrid Organic Acid Technology OAT— OAT plus a low dose of silicate.

Nitrited Organic Acid Technology (NOAT)—OAT with no silicates or phosphates

Nitrited Molybdate Organic Technology (NMOAT) – Contains Molybdate and used mainly with diesel engines.

Poly Organic Acid Technology (POAT) – Variation of OAT

Common organic corrosion inhibitors

Organic acid corrosion (OAC) inhibitors or organic acid technology (OAT) coolant can act as cathodic or anodic inhibitors, or a combination of the two. Common organic acid compounds are: 2-ethylhexanoic acid, sebacic acid, azelaic amines, urea, Mercaptobenzothiazole (MBT), benzotriazole e toliotriazol, aldehydes, heterocyclic nitrogen compounds, sulfur-containing compounds and acetylenic compounds and also ascorbic acid, succinic acid, tryptamine, caffeine and extracts of natural substances. OAT coolants also contain an azole additive as a copper corrosion inhibitor.

Organic acid compounds are film-forming with a strong

organic acid antifreeze versus universal antifreeze

Organic acid antifreeze comes in different colors

affinity for metal surfaces. Organic acid formulas develop a protective hydrophobic film on the metals to form a barrier. They offer much longer life than inorganic inhibitors, but take much longer to form a protective film than inorganic inhibitors.

Organic acid inhibitors protect aluminum and cast iron components. They are non-abrasive, so they don’t damage water pump seals. However, the exact formulation MUST be compatible with the plastic and rubber components used in a particular engine/cooling system combination.

Since car makers vary the types of rubber and plastics by year, make, model and engine, there are simply too many variations for any antifreeze manufacturer to claim their product works in all makes, all models and is universal.

Some car makers recommend Hybrid Organic Acid (HOAT) antifreeze formulas that use an organic anion as the primary corrosion inhibitor, along with an inorganic corrosion inhibitor. HOAT, for example, may use organic acid with a low silicate inorganic corrosion inhibitors. The inorganic corrosion inhibitor provides rapid passivation until the organic acid portion can take full effect. Yet the low silicate concentration doesn’t damage water pump seals. HOAT coolants also contain an azole additive as a copper corrosion inhibitor.

How can antifreeze manufacturers claim their product is all makes, all models or universal?

They really can’t. Generally, all makes all models universal antifreeze is 96% ethylene glycol and just 2 to 5% inhibitors. Since the product is billed as all makes, all models, it’s can’t possibly be vehicle specific, so it’s really a compromised product that provides LESS corrosion protection than the factory formula. To cover their bases, these all makes, all models universal antifreeze formulas use a small amount of every inorganic inhibitor, which causes corrosion by itself because the inhibitors interact poorly with each other.

use the correct coolant, never a universal antifreeze

In fact, many car makers have issued service bulletins warning not to use the wrong antifreeze just for this reason. In addition to interactions between inorganic inhibitors, there’s also the issue of incompatibility between the all makes, all models universal antifreeze and the rubber and plastics used in the engine and cooling system components.

So mixing different types of antifreeze coolants or add the wrong antifreeze coolant can actually CAUSE corrosion, pitting of water pump, rust formation in radiator and total cooling system degradation.

Using the wrong antifreeze coolant can cause extensive cooling system damage

Shops like to use all makes, all models antifreeze coolant because they don’t have to stock vehicle specific antifreeze or tie up their repair bay waiting for an antifreeze delivery from the local dealer. However, if a shop uses all makes, all models universal antifreeze coolant in your vehicle and it’s not fully compatible the damage won’t show up for at least a year. By then you won’t connect the dots to realize that the coolant flush with the wrong coolant is what damaged your radiator, heater core or water pump. Good luck pointing the finger at the shop at that point!

Why do shops and parts stores sell and use a universal or multi-vehicle coolant?

Simple, shops and auto parts retailers don’t have the shelf space to stock every car maker’s specific type of coolant. Many universal or multi-vehicle coolants have a neutral color, neither bright green nor orange. If the vehicle is just low on coolant and you’re using a universal coolant to top off the level, you probably won’t compromise the anti corrosive capabilities since the system is already passivated. However, there’s no way of knowing if the new universal coolant is compatible with the corrosion additive package which could result in corrosion inhibitor drop out.

warning about using a universal antifreeze in your car

Which water to use when mixing antifreeze concentrate or topping off the system?

Ask any car buff which water to use when mixing antifreeze concentrate or topping off  a cooling system, and they’ll tell you to use distilled water. Well, that’s certainly better than hard tap water. But distilled water can still contain minerals that can react with metal and your antifreeze to form corrosion and deposits. You want de-ionized/de-mineralized water.

Other antifreeze additives

In addition to corrosion inhibitors, all antifreeze formulas contain an anti-oxidant, anti-cavitation and anti-foaming additive, along with a identifying dye.

What determines antifreeze life?

Ethylene Glycol never wears out, but the corrosion inhibitor,anti-oxidant, anti-cavitation and anti-foaming additives do wear out. How long the antifreeze lasts is directly related to type and amount of the corrosion inhibitor in the formula. If you don’t change your antifreeze coolant at the recommended intervals, you risk causing extensive and expensive damage to your radiator, heater core, heater tubing and water pump.

©, 2017 Rick Muscoplat



Posted on by Rick Muscoplat

Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN