View all results


  1. Home


1 March 2016

The topic for this column is cooling system maintenance. We last touched on this topic back in 2010 when we reviewed the different types of modern engine coolants in use.

Since that time, the need for enhanced cooling system maintenance has grown. The demands on engine cooling systems are driven by changes in engine design and architecture, as well as upgrades in federal emissions regulations.

Unfortunately, many truck and equipment owners and operators are still servicing the cooling systems of their equipment like they did decades ago, giving only cursory thought to system maintenance. With the increased demands placed on today’s cooling systems, this is no longer good enough.

Failing to adequately maintain cooling systems can lead to very costly failures that can range from leaking hoses and seals to completely corroded and failed pumps, housings, tubes, and even radiators and coolers. Up to 60% of engine failures can be attributed to cooling system failures and most of these failures are due to insufficient system maintenance. So let’s review this increasingly important subject, with hopes that some of these system failures can be prevented.

While water makes a great heat-transfer medium, it alone cannot be used as the coolant in modern engines. Besides removing heat, coolants also need to remain stable in extreme temperature fluctuations. Since water freezes at 32 degrees F and boils as 212 degrees F, and water alone is very corrosive and is a strong solvent, it is not appropriate for the job. Also, cooling systems in heavy duty diesel engines need to protect the cylinder liners from a condition known as “cavitation erosion” and there needs to be some lubrication for the water pump.

Water alone cannot do all of these things, so obviously something else needs to be mixed in to address all of these concerns. Engine coolants are a chemical blend of water with ethylene glycol (or propylene glycol) and other additives designed to extend the operating temperature range and combat corrosion, erosion, deposit formation and wear within the cooling system. The glycol/additive mixture is known as “antifreeze,” as the original intent was to prevent freezing of the water in early liquid-cooled engines. Since then, the demands have grown beyond freeze prevention alone, but the name “antifreeze” carries on.

A proper engine coolant is made up of a 50/50 blend of antifreeze and water. This can be created by mixing concentrated antifreeze with water or by obtaining a “premix” solution that has the antifreeze already blended with water in the proper ratio.

There are basically two different types of coolants suitable for heavy duty use, either the older “fully formulated” type coolants with supplemental coolant additive (SCA) technology, or the newer “extended life” coolants that use organic acid technology (OAT). There are also hybrid designs that blend the 2 types and these are known as HOAT coolants (hybrid OAT), or NOAT coolants (OAT-type coolant blended with Nitrite additives).

Most new trucks and off-road mobile equipment come factory-filled with OAT-type coolants, which have several advantages over the older SCA type coolants. In particular, they offer longer service life and greater protection of the cooling system when properly maintained.

It is important to note a concern that has arisen over the past several years, which is the increased use of aluminum in the construction of many cooling system components, such as radiators, oil coolers, thermostat housings, water pumps and tubing. Nitrites used in some coolants can damage aluminum, so for fleets with more-modern equipment with high aluminum content, consider switching to a nitrite-free, second-generation OAT extended-life coolant that can help to minimize aluminum corrosion in cooling systems.

While it is permissible to mix different types of coolants in an emergency, ideally this should not be done on a regular basis, as the mixture tends to dilute the strength of both types of coolant. For this reason, we always recommend to our customers that they settle on one type of coolant and stick with it for all of the equipment in their fleet.

This strategy helps to prevent misapplication and accidental cross-contamination. On many system failure investigations, cross-contamination of coolants is at least partially responsible for the failure. It is wise to reduce the chances of this happening by removing all of the non-conforming coolants from your operation. Please be sure to dispose of them properly.

The quality of the water used is very important as well. The hardness (mineral content) of water varies by locale, with many areas having very hard to extremely hard water. Higher levels of mineral content can stress the coolant and lead to scale formation along the interior passages of the cooling system. Scale deposits greatly reduce the ability of the cooling system to transfer heat away from the engine components. A thin layer of scale (.025”) can reduce the heat transfer rate by 40%.

Because of this issue, it is important to use softened water when blending with antifreeze. Ideally, deionized water should be used, which is a component in most “premix” coolants. If you are going to use concentrated antifreeze and blend the coolant yourself, you should locate a good source of soft water. If you plan on using the tap water from your local utility, it is highly recommended that you send a sample of the water out to a lab to determine its hardness level. In our experience, the hardness level of most tap water around the country is too high to be used in cooling systems.

Failure to acknowledge this as a legitimate concern will reduce the effectiveness of your cooling system maintenance program. As mentioned in the beginning of this article, the demands placed on modern cooling systems are much greater today than ever before. While you may have gotten away with using poor quality water in your cooling systems in the past, those days are over.

This concludes our initial review of engine coolants, antifreeze, and water. In the next edition of the HD Focus newsletter, we will cover proper system maintenance and the importance of coolant analysis. In the meantime, if you require more information or assistance with selecting a proper coolant, please contact a Castrol® field engineer or sales representative.