Hopefully, the information in this article can help you begin to make some sense out of the products available and how to maintain your heavy-duty engine-cooling systems.

Engine coolant is made up of water, glycol and inhibitors. Water alone provides excellent heat transfer; however, antifreeze is needed to prevent freezing while also raising the boiling point. The glycol portion of antifreeze comes in two varieties, the most popular being ethylene glycol (EG). For environmentally sensitive applications, propylene glycol (PG) is also an option.

The inhibitors are responsible for protecting the cooling system against corrosion and cavitation. Inhibitors are the main cause of the confusion due to the various packages available. The three inhibitor technologies available are IAT, OAT and HOAT.

Inorganic acid technology

Inorganic acid technology (IAT) is used for what many refer to as “traditional or conventional” coolant. These coolants use inhibitors like silicate, phosphate, borate and nitrite to form a protective physical barrier on the surfaces within the cooling system. Due to this design, these inhibitors deplete rapidly and must be replenished at regular intervals with supplemental coolant additives (SCAs).

SCAs can be replenished in liquid form or through the use of a coolant filter. The proper test strip should be used to determine the type and quantity of the SCA to be added.

IAT coolants come in three variations: automotive/light-duty (ASTM D3306), low-silicate heavy-duty requiring an initial charge (ASTM D4985) and pre-charged low-silicate heavy-duty (ASTM D6210).

Automotive-type coolants, when used in light-duty engines, do not require SCAs. Heavy-duty coolants should be used for all heavy-duty engines to ensure proper protection, especially against cavitation. Wet-sleeve diesel engines are the most susceptible to cavitation, while most dry-sleeve/parent bore-type engines do not have issues with cavitation.

The “charge” of the product refers to the addition of SCAs; pre-charged coolant is ready to use while others require an initial charge to be added. IAT-coolant SCAs should be maintained at every oil change, while the coolant drain interval can be up to two years or 2,000 hours.

Organic acid technology

Organic acid technology (OAT) is used for the more recent, true extended-life coolants (ELCs). These use carboxylate inhibitors that react at the site of corrosion/cavitation only when needed. These inhibitors deplete at a very slow rate, meaning longer drain intervals and no need for SCAs.

There are two major variations of OATs in the heavy-duty sector: nitrited OAT (NOAT) and nitrite-free OAT (OAT-NF, OAT Global). Due to the lack of standards regarding coolant labeling, you may have to read the label a little further to find out if a product simply labeled “OAT” contains nitrite or not. In general, “global” formulas will be nitrite-free.

Nitrite is used for protection against liner cavitation; some OEMs require a nitrited coolant. Nitrate-free is gaining in popularity among all OEMs, especially those with European-based engines. To those OEMs, the modern OAT coolants provide adequate liner protection, while the elimination of nitrite reduces the potential for damage to aluminum components when subjected to the heat of modern engines.

OAT coolants are becoming very common; every new commercial truck leaves the factory with an OAT coolant. Switching to an OAT coolant can meet the needs of nearly every engine while reducing your maintenance costs and coolant inventory. Converting to an OAT from an IAT requires nothing special other than switching to a coolant filter with no SCA in it.

You may also opt to remove the coolant filter altogether. The drain interval for OAT coolants is significantly longer than for IAT coolants and can be as high as five to eight years or 10,000 to 15,000 hours. Some can go even longer, but as with any coolant, periodic monitoring is still a good practice.

Hybrid organic acid technology

Hybrid organic acid technology (HOAT) is a combination of both IAT and OAT. HOATs are not commonly used for heavy-duty applications; however, there are two common variations in the automotive sector.

European HOAT contains silicates but is phosphate-free, primarily due to regional issues with hard water. Asian HOAT contains phosphate but is silicate-free partially due to water pump seal issues. In some cases, an HOAT will be used in a heavy-duty application that may require SCAs.

Understanding the different coolants and their applications is just one part of a good coolant maintenance program. Certain key maintenance procedures are not specific to any type of coolant.

• Freeze point of the coolant should be checked and adjusted down with concentrate or up with distilled water.
  
  
• Verify that the pH is within the specific coolant’s allowable range. A high pH can indicate excessive SCAs, which can create gel from dropout. Low pH, within the coolant’s service life, can indicate an air leak, combustion leak or accelerated cavitation.
  
  
• Testing for electrolysis can be done using a digital volt meter with the negative lead on the negative battery terminal and the positive lead dipped into the radiator. A reading of more than 300 mv could indicate a potential issue.

Hopefully, the information in this article can help you better understand the engine coolants you may run into and how to maintain them. As a final note, while coolant color can be a useful clue, it should not be considered a definitive descriptor in determining the coolant type.  FG

Vinny Endres is a mechanically savvy Wisconsin dairy farmer.