Engine Coolant types — The difference between coolants

Understanding Different Coolant Types: A Comprehensive Guide

Understanding engine coolant types is vital for anyone serious about maintaining their vehicle. Over the years, I’ve worked with countless engines and learned that choosing the right coolant is critical to ensuring the longevity and efficiency of your cooling system. Let me walk you through the different engine coolant types, their composition, and their impact on your car.

Automotive coolant types are divided into two main categories: the older “Green” Inorganic Acid Technology (IAT) coolants and the newer organic acid technology coolants (OAT, HOAT, PHOAT, and NHOAT).

A Look At The Two Most Common Coolant Types— OAT and HOAT

OAT —Organic Acid Technology— DexCool by GM

You’ll find DexCool OAT coolant in most GM vehicles. OAT coolant offers exceptional, long-lasting protection for aluminum engines.

Concentrated OAT coolant is still built on a 95% glycol base fluid. The biggest difference between OAT and IAT coolant is that OAT doesn’t use silicates, phosphates or borates. Instead, they use sebacate and carboxylic acids, azoles, 2-ethylhexanoic acid (2-EHA), aliphatic mono- and dicarboxylic acids and tolyltriazole as the anti-corrosion additives.

OAT coolants prevent corrosion by bonding to the metals at the molecular level. They protect up to 150,000 miles or five years. While OAT additives last much longer than IAT additives, they also take much longer to start working, several thousand miles of driving before they take full effect.

Advantages of OAT coolant

• Longer life
• Better able to protect aluminum than silicates and phosphates
• Non-abrasive, so it doesn’t wear out water pump seals.

Disadvantages of OAT coolant

OAT coolant takes longer to provide protection. They usually don’t reach maximum protection until the vehicle has driven 3,000 to 5,000 miles. DexCool can react with air to form sludge if you operate your engine for long periods with low coolant levels

Hybrid Organic Acid Technology (HOAT) coolant type

HOAT coolant is designed to combine the best of both worlds— OAT for long term protection, with either silicate or phosphate to provide quicker protection until the OAT kicks in.

Depending on the carmaker, HOAT includes OAT and silicate or OAT and phosphate,

• Asian carmakers prefer phosphate in their HOAT coolants to provide immediate corrosion protection until the organic acids take effect. They also like phosphate because it doesn’t have the abrasive effect of silicate additives.

• European carmakers, conversely, prefer OAT with silicates and no phosphates.

In other words not all HOAT coolants are the same

What’s in all coolants?

Concentrated engine coolant is approximately 95% mono-ethylene, polyethylene, or polypropylene glycol. The remaining 5% consists of additives like lubricants, anti-foaming agents, buffers, antioxidants, and anti-corrosion compounds. These additives are what differentiate the various engine coolant types and determine their compatibility with specific engines.

Once a concentrated coolant is mixed with water in a 50:50 ratio, the result is a coolant mix of 47% Ethylene glycol, 50% water, and ~ 3% anti-corrosion additives.

Understanding the “G” Engine Coolant Types

The “G” coolants come from the trade name Glysantin of BASF in Europe and Valvoline (Zerex) in the United States. They’re considered a HOAT-type coolant. Here’s a quick summary of the G engine coolant types.

• G05: HOAT coolant with Nitrites, low silicate, reduced pH, and phosphate-free. It should not be used in aluminum engines due to the possibility of nitrate corrosion. It contains silicate, so it should not be used in Asian engines. It should not be used in European engines because it contains phosphates and is low in silicate.
• G30, G34: Silicate and phosphate free
• G11: Blue VW used before 1997
• G12: Pink/Red VW 1997 (purple VW 2003) HOAT formulation, Phosphate free
• G48: Dark Blue, Low silicate, and phosphate-free. Nitrates, amines, phosphate (NAP) free

G-05 is used as a universal coolant by many shops to avoid stocking multiple types of coolants. It is a low silicate, no phosphate formula. However, since it contains silicates, it should not be used on Asian vehicles.

Engine Coolant Types by Carmaker

VW/Audi Pink—  Contains some silicates and an organic acid and is phosphate-freeMercedes/Ford Yellow— Contains low amounts of silicate and no phosphate
Ford Yellow—  Contains low silicate, no phosphate, and is dyed yellow for identification
Honda Blue— A special low-silicate coolant with just one organic acid
European/Korean Blue— Contains low silicates and no phosphates
Asian Red— Contains no silicates but has some phosphate

What About “All Makes, All Models” Universal Coolants: Are They Truly Universal?

Question: How can one coolant be universally compatible when all carmakers have different specifications? Answer: It cant

Here’s the truth: “Universal” coolants are a compromise. These products are HOAT-based coolants, were the coolant manufacturers have thrown in the kitchen sink to cover their butts. So you’ll find nitrites, silicates, and phosphates in the kitchen sink so they cover all the bases.

Unfortunately, these “universal” blends don’t do anything well. For example, it may have too little silicate to meet one carmaker’s specifications or too much silicate for another. The same applies to phosphates or nitrates. For modern engines, especially those with aluminum components, nitrites can cause more harm than good. In my opinion, when choosing an engine coolant type, you should always stick with the recommended coolant and avoid all universal “all makes, all models” coolant.

Universal coolant isn’t any cheaper than the recommended coolant, and it doesn’t work as well as the recommended coolant. Why risk cooling system failures that could cost thousands of dollars just to save $10 on coolant?

If one coolant can work in all vehicles, why does Prestone make 8 engine coolant types?

Prestone promotes its All-Vehicles Coolant. But if it works so well in all vehicles, why do they still make 8 other types of coolants that do meet carmakers’ specs? See this post for more information on Prestone All Vehicles coolant.

What happens if you use the wrong engine coolant type?

Using the wrong coolant can lead to scaling, pitting, or even catastrophic engine damage. If you’ve mixed coolants in the past and noticed brown sludge or poor cooling performance, it’s time to flush your system and start fresh with the correct type. Trust me, it’s cheaper than replacing a radiator or heater core.

What additives are used in IAT coolant?

Borate — Used to reduce acidity. It’s generally not used in OAT or HOAT coolants because they maintain a different pH, and borate would throw the pH out of whack.

Nitrite — Used in cast iron engines to prevent corrosion and cavitation. However, Nitrite doesn’t work well with newer aluminum engines. If it is used in an aluminum engines, the coolant must contain other additives to protect the aluminum.

Phosphate — Phosphate lays down a protective film on cooling system metals to prevent corrosion. If you’re mixing concentrated coolant that contains phosphate, it’s critical to use distilled water as tap water (hard water) can cause the phosphate coating to flake off and form layers of scale that can clog the radiator and heater core.

The main advantage of Phosphate is that it quickly lays down a “passivating” layer on metal surfaces. So it protects right away. However, phosphate coatings don’t last very long.

Silicate — Often used as a substitute for phosphate. It’s considered another fast-acting acid that lays down a metal coating barrier to protect metals from corrosion. Silicate works fast to protect but has a short life like phosphates. However, some Asian carmakers believe that silicates are abrasive and wear out water pump seals, so you generally won’t find silicates in Asian coolants. Silicates have one other drawback: they reduce heat transfer.

How does IAT coolant work?

The Silicate or phosphate additives form an anticorrosive coating on all metals in the cooling system. The coating acts as an Anodic layer of protection. Once the anodic coating layer is higher than any cathodic current in the solution, the system is considered “passivated,” preventing electrolysis. In other words, the anodic coating prevents the transfer of electrons from one metal to another, something we call corrosion.

Downsides to IAT coolant technology:

• Short life — The silicates and phosphates precipitate out of the solution, so they have a short life of less than 30,000 miles or about 2 years.
• Borate— Works as an anodic corrosion inhibitor for cast iron engine parts but is corrosive to aluminum and aluminum alloys
• Silicates and phosphates— Abrasive, so they cause wear to water pump seals
• IAT green coolant reacts poorly with hard water— It can form scale in the cooling system that can plug the radiator and heater core.
• Nitrates— Short life and don’t work well to protect aluminum or aluminum alloys.
• Long Term Pitting —As the passivating film deteriorates, the metals develop pitting, and the corrosion accelerates.

Silicates and phosphates are designed to protect copper, brass, cast iron and aluminum. It is NOT recommended for use on newer cars that were filled with OAT or HOAT coolants.

Since most modern engines are built with aluminum engines, radiators, water pumps, and plastics, IAT coolant is no longer the best choice.

©, 2022 Rick Muscoplat