Organic acid technology (OAT) coolants have been around for more than three decades and offer proven cost savings and performance benefits. They’ve become the preferred option for most heavy-duty engine manufacturers, however, their advantages aren’t widely known or understood.
According to Technical Paper 881270, a frequently cited report published by the Society of Automotive Engineers (SAE), roughly 40% of all problems in heavy-duty diesel engines are related to the cooling system. Choosing the right coolant, and maintaining it correctly, is therefore critical to the uptime and service life of your equipment. It’s also essential to be aware of the hidden costs of cheap coolant. While a less expensive coolant may save you a few dollars today, it may result in costly repairs down the road.
This article will provide a high-level overview of OAT coolants and explain the many benefits that make them ideal for heavy-duty engines.
What Are OAT Coolants?
“Organic acid technology (OAT) coolant was developed to extend service intervals and reduce the total amount of maintenance required over the life of the coolant,” said William Huff, a senior chemist for Fleetguard, a brand of Atmus Filtration Technologies. “It achieved both goals with great success and can potentially last up to 1 million miles (1.6 million km) or more — the point where most diesel engines need to be rebuilt.”
Introduced in Europe in the late 1980s, OAT was widely adopted by North American manufacturers in the mid-1990s and is typically used in most newer vehicles today. In fact, many original equipment manufacturers (OEMs) use OAT or one of its variants exclusively.
OAT coolants utilize organic carboxylic acids as their primary corrosion inhibitors. A higher concentration of these additives — typically 20,000 to 30,000 ppm — enables them to deliver more efficient corrosion protection than conventional inorganic alternatives.
OAT coolants also require less frequent replacement because their additives are depleted at a much slower rate. No supplemental coolant additives (SCAs) or extenders are needed. End users can simply top off their system with more of the same OAT coolant periodically.
On the other hand, conventional inorganic additive technology (IAT) coolants have a typical service interval of around 30,000 mi (50,000 km), or about 700 hours of operation, whichever comes first. They also require frequent maintenance because the additives they use to protect engines deplete over time and need to be replenished regularly with SCAs. As a result, coolant testing is recommended at every oil change.
OAT Coolants Aren’t Created Equal
OAT coolant chemistries can vary a fair bit. Each has a unique additive package (we’ll discuss some of the more common variations later in this article). This is in contrast to conventional inorganic coolants, which have much more similar chemistries, typically some combination of nitrite, molybdate, silicate and borate additives.
Although OAT coolants offer significant advantages, it’s important to choose your formulation wisely. Some OAT coolants contain 2-ethylhexanoic acid (2-EH or 2-EHA), an additive that can damage silicone components like head gaskets, heater hoses and radiator hoses. 2-EH is banned for public use in Europe because it’s considered a hazardous material, but it’s still widely used elsewhere because it’s inexpensive to manufacture and highly effective at protecting cast iron.
“2-EH will attack your silicone, and it’s not just related to the engine. It can hit any of your components. For example, there’s been a big industry move to use silicone heater and radiator hoses. So even if your engine is silicone-free, other components of your cooling system may not be,” Huff said.
Read ingredient labels carefully. Although the presence of 2-EH must be disclosed by law, the term “proprietary inhibitors” is sometimes used to hide it. Most other organic acids don’t have the same issues as 2-EH.
At a minimum, look for OAT coolants that meet the ASTM D6210 standard for heavy-duty engines. For best results, choose one that’s tested and approved for your OEM’s engines, such as CES 14603 or CES 14439 for Cummins, DFS93K217ELC for Detroit Diesel, or similar specifications for other manufacturers. Another number to look for is the Technology & Maintenance Council Recommended Practice (TMC RP) 364, a fleet purchasing specification for OAT extended life coolants for heavy-duty vehicles.
Choose an OAT coolant that’s 2-EH free to best protect your engine and cooling systemFleetguard
Other Types of OAT
Another common type of OAT is nitrited organic acid technology (NOAT). These variants primarily use nitrites as their corrosion inhibitors. Some OEMs are promoting NOAT coolants because they do a good job of protecting cast iron components, like wet sleeve liners, from pitting caused by cavitation. Beware, however, that NOAT coolants are NOT right for every engine. At higher pH levels, nitrites can aggressively attack aluminum, increasing the chances for pitting and corrosion. This is a growing concern, as aluminum is becoming more common in many engine components, including radiators, heater cores, exhaust gas recirculation (EGR) coolers and some oil coolers. Check with your OEM or coolant supplier to make sure NOAT is appropriate for your equipment before using it.
Phosphated organic acid technology (POAT) coolants primarily use phosphates as their corrosion inhibitors. Some OEMs are attempting to use POAT formulations to achieve even longer coolant or water pump life, but as of this writing, no publicly available data has been released to support these claims. Phosphates are more stable than nitrites and offer better protection for aluminum but are more likely to form scale if mixed with hard water. This isn’t an issue if you use fully formulated (premix 50/50) POAT coolants, but users of concentrate should mix with the purest water source possible — preferably distilled, deionized or filtered with reverse osmosis (RO).
Silicate-enhanced organic acid technology (Si-OAT) is another coolant variant, which uses silicate-based formulations to inhibit corrosion. Si-OAT coolants are primarily recommended or required by European OEMs and engines from other manufacturers that are marketed in Europe, such as Ford and Lexus. Si-OAT coolants provide good protection for aluminum components and are less likely to form scale in hard water (common in Europe) than POAT coolants. The primary tradeoff is that Si-OAT coolants can form a filter-clogging silicate gel if the pH falls too low.
Hybrid organic acid technology (HOAT) or extended-life coolants (ELCs) blend conventional coolants with OAT. Although not as efficient as pure OAT, many hybrid coolants still offer a big jump in performance over their conventional counterparts. Service intervals can be extended up to 150,000 mi (240,000 km) or 4,000 hours. Since they still contain some inorganic additives, hybrid coolants may require the use of SCAs or extenders.
Table 1. Coolants by Technology TypeFleetguard
Mixing different types of OAT coolants is NOT recommended, even if the OEM approves more than one variety for use in their equipment. Although a few manufacturers ensure their OAT products are compatible, it can be risky to take this for granted. For example, some coolants can be safely mixed, but it is often a rare exception. Other combinations could cause difficulties because of different base ingredients or proprietary chemistries.
Unless you’re stranded in the middle of nowhere with coolant running low, it’s best to drain and flush the system before switching between OAT products, rather than topping off one type with another, even if they’re made by the same manufacturer. If you have an emergency and just need to top off with whatever’s available, most OEMs recommend trying to keep at least 80% of one technology in the system to preserve coolant performance.
Upgrading from a conventional or hybrid coolant is simple: drain the system, flush it with water, and refill it with OAT.
OAT Delivers Flexibility and Simplified Maintenance
In the past, heavy-duty engine coolants couldn’t be used in light-duty applications and vice versa: you needed one type of coolant for heavy-duty diesel engines and another for automotive applications. OAT coolants, by contrast, can be used in either type of engine, making them ideal for mixed fleets.
“Traditionally, you didn’t really have heavy-duty engine coolants that you could also use in light-duty applications. They didn’t quite get along. But you can run OAT across the board — it’s much simpler and compatible with just about everything. I even use it in my pickup truck.” Huff said.
With a good OAT product, you’ll only need to test your coolant every 300,000 miles (480,000 km), or about 6,000 hours of operation, whichever comes first. No SCAs, extenders or special filters are needed.
Test strips are available to help you determine when it’s time to top off. Note that these are typically brand- and technology-specific because of the diversity of OAT coolant chemistries. Although test strips can provide you with a quick assessment of your additive levels, they can’t detect the presence of metals in your coolant. Consult your coolant supplier to ensure you’re testing correctly.
An Investment in the Long Haul
Although the up-front costs of OAT coolants is a bit higher, their superior formulation offers better engine protection that can pay for itself quickly. You’ll also have fewer testing and maintenance hassles.
It’s important to remember that there’s no “one size fits all” coolant. Different OEMs recommend different types of OAT coolants. Consult your coolant supplier to determine the best OAT formulation for your application.
