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The engine's cooling system serves a number of purposes, including keeping the engine running at its most efficient temperature no matter what the operating conditions are. With the many new developments to engine coolant over the years, confusion has grown over which color or formulation of coolant is acceptable.

Coolants at a crossroad

April 10, 2017
Coolant technologies are causing confusion.

Prior to 1927, a variety of different compounds were used as cooling system liquids, including common kitchen ingredients such as sugar, honey and molasses. That changed when Prestone introduced the first all-season, ethylene-glycol-based cooling system fluid.

Ethylene glycol, with the integral corrosion inhibitors, remains the major component of antifreeze/coolant (AF/C) to this day.

When maintained and working properly, AF/C provides four key functions:

- Provides efficient heat transfer to control critical engine temperature.

- Increases the boiling point to help prevent boilover and overheating failures.

- Provides freezing protection to prevent freeze-ups or non-starts in the lowest temperatures.

- Provides effective inhibition of corrosion for all cooling-system metals.

If the AF/C is unable to satisfy these requirements, the vehicle’s emissions, fuel economy, horsepower and durability of engine components will be compromised.

The AF/C industry is currently at a crossroads due to Nitrite-related issues. Here’s how we’ve arrived.

Evolution Of Heavy Duty AF/C

The heavy duty market has historically relied on Nitrite technology to protect against cylinder liner cavitation. Conventional Inorganic Additive Technology (IAT) with nitrite and/or molybdenum had traditionally provided acceptable protection to heavy duty cooling systems.

However, in the early 1990s, manufacturers began to introduce extended life Organic Acid Technology (OAT) fluids which contained Nitrite. This resulted in the introduction of Nitrite Organic Acid Technology (NOAT).

The goal of these fluids was to provide the same level of protection to the cylinder liner with extended time between when the coolant had to be re-inhibited or changed.

In 1994, Caterpillar released its EC-1 coolant specification for NOAT coolant. The specification was for a 150,000 miles or 3,000-hour coolant that could be extended to 300,000 miles or 6,000 hours with the addition of an extender.

Then, in 1999, Caterpillar extended the service life specifications for NOAT coolants to 300,000 miles or 600,000 miles with an extender. During this period, many OEMs moved away from IAT in favor of NOAT technology and extended life formulas.

Increased Pressures

In response to the rising cost of fuel and growing environmental concerns, the next decade brought increased pressures to improve emissions and obtain a higher fuel economy. To achieve these results, significant design changes were needed to both vehicles and engines.

Lighter materials were used to build engines and cooling systems, including a move from copper/brass to aluminum radiators. Initial aluminum radiators were manufactured by either assembly lines or through a vacuum brazing process.

Then, a new process, controlled atmosphere brazing (CAB), was developed to improve efficiency. It paved the way for increased production, but with some unforeseen issues.

The CAB process leaves behind varied levels of residual brazing flux on the aluminum surface, which can react with certain coolant inhibitors. One important inhibitor affected by CAB is nitrite, the key inhibitor used to protect liners from cavitation damage.

As a result, fleets began to experience a quick decrease of nitrite concentrate with a pH spike in their coolants, accompanied by an increased corrosion rate on aluminum cool system components. This increased corrosion led to the disbursement of aluminum corrosion byproducts throughout the cooling system, causing significant cooling system problems and buildup in coolant filters.

While vehicles with copper/brass radiators don’t have this issue, vehicles with CAB brazed aluminum radiators were left vulnerable.

A Shift Creates Confusion

Heeding concerns that NOAT wasn’t providing the same level of protection for aluminum systems, a number of OEMs changed their factory fill coolant from NOAT to nitrite free extended life coolant (NF OAT).

Navistar has been factory filling some engines with NF OAT since 2010. In 2016, Detroit Diesel announced a move to NF OAT coolant. Cummins is currently qualifying NF OAT coolants for its engines.

While these changes from NOAT to NF OAT eliminate issues caused by nitrites, it opened the door for another issue: confusion around the AF/C’s color.

The Technology & Maintenance Council (TMC) has proposed guidelines for the standardization of AF/C color through its Recommended Practices. Since these are guidelines and not steadfast regulations, OEM and coolant manufacturers are technically able to choose their own color dyes.

Comprised of a broad collection of experienced fleets, equipment suppliers and service providers, TMC ( is the only industry association focused solely on truck technology and maintenance. 

Circumnavigate Coolant Complications

With all of these Nitrite-related issues, the good news is that there’s a dialogue taking place within the industry. The goal is to develop a standardized color code for all coolant technologies to make it easier for the fleets to identify their coolant types. In the meantime, here are some solutions to make sure your fleet is covered.

- Work with a skilled technician – Technicians can test for, identify and correct any issues with your cooling system. Take the time to ask your technicians about their experience with these issues to determine if they’ll be able to properly care for your fleet.

- Use a trusted formula – By way of example, to avoid any confusion for fleets, Prestone clearly differentiates its three AF/C technologies: IAT (purple), NOAT (red) and NF OAT (yellow). For clarity, Prestone has implemented the same color codes for accompanying supplemental coolant additives (SCA), extenders and test strips. Prestone offers test kit mailers that provide fleets a quick way to determine the best approach for cooling system maintenance.

- When in doubt, flush it out – It is imperative that drivers and fleets know exactly what type of AF/C is helping run their engines. If all else fails, flush out your cooling system and start fresh with a clearly labeled formula.

About the Author

Collin Dilley | Vice President of Technology, Prestone Products Corporation

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