What is the controlled atmosphere brazing (CAB) process for manufacturing aluminum radiators, and how does this pertain to fleet vehicles?

The CAB process refers to how the aluminum parts of a radiator are joined together. This is done using a flux or chemical cleaning agent that prepares the aluminum for brazing. The CAB process has been around for approximately 15 years and has become more popular over the last few years, including with waste fleet vehicles.

Why are CAB radiators a concern?

The outside of the radiator that is exposed to the atmosphere becomes oxidized or passivated over time, meaning a natural protective coating forms on the aluminum. However, inside the radiator, the aluminum treated with the flux remains un-passivated and lacks that protective layer.

When a nitrited coolant is introduced to the radiator, it has a tendency to react with the un-passivated or unoxidized aluminum. This can create ammonia, which leads to an unpleasant odor, and other reactions that can cause the formation of precipitants that clog small orifices in the coolant system.

Dan Holdmeyer, industrial sector manager for Chevron Lubricants, addresses common questions about fleet coolant systems

How do these CAB radiators affect nitrite-free coolants?

When using a nitrite-free coolant, the presence of flux can change the concentration of the additives in the coolant depending on the additive chemistry. This can cause the formation of precipitants, which again, can clog small orifices in the cooling system. pH imbalance, either too high or too low, can also lead to coolant system metal corrosion.

What can be done to protect against the degradation of coolants and corrosion of heavy-duty coolant systems containing CAB-processed radiators?

Some manufacturers have addressed the issue by offering a radiator conditioner that effectively passivates the metal inside the radiator. This allows for the use of a coolant containing nitrites, which some OEMs recommend for protecting cylinder liners from cavitation, while mitigating the problems caused by the un-passivated aluminum and flux. While some manufacturers have gone to a nitrite-free organic additive technology (OAT) specification due to the aluminum radiator issue, a few OEMs still call for nitrited OAT or NOAT coolants. Most equipment users in North America, therefore, are still using NOAT-based coolants, even if they have mixed fleets, and choose to use the radiator conditioners in new equipment or replacement radiators.

Is there a more comprehensive, less labor-intensive method to protect coolant systems and the coolants in today’s systems?

At Chevron, we have come up with an alternative solution, which is to change the composition of the coolant rather than treating the aluminum with a conditioner. Our new Delo® ELC Advanced extended life coolant is a NOAT formulation with patented technology that controls the reaction with the aluminum and the flux to extend system and coolant life. With Delo ELC Advanced, equipment operators will no longer need to rely on a conditioner to reduce the risk of a chemical reaction with the nitrite and un-passivated aluminum in their coolant systems.