Equipment Type

Diesel-Coolant Industry Heats Up Over Nitrite

A look at how opinions differ about antifreeze formulations

January 23, 2018
Color has become more of a marketing tool than an indicator of antifreeze type

”In an ideal world, in which no one ever touched the coolant and the vehicle never leaked, a high-quality extended-life coolant would be virtually maintenance-free. But this is not an ideal world.”—Stede Granger, P.E., OEM technical services manager, Shell Global Solutions (U.S).

In talking with a variety of machine and vocational-truck owners who work in the “real” world, Construction Equipment is aware that knowledge of diesel-engine coolant (ideally, a 50/50 mix of antifreeze and distilled/deionized water) varies from those who have no idea what’s in the radiator of their backhoe, to fleet managers who can discuss specific additives used in a particular antifreeze formulation. Considering this range of knowledge, we offer a quick refresher.

Antifreeze basics           

Virtually all concentrated heavy-duty antifreeze is roughly 95 percent ethylene glycol (or propylene glycol, which is somewhat less toxic) and 5 percent additives and water. Formulations differ by virtue of their additive chemistry, but all diesel-antifreeze additive packages have the same basic tasks—to deter such culprits as rust, scale, corrosion, aeration, acids, and the process of cavitation/erosion/corrosion, which can pit the outside surface of a diesel’s wet cylinder liners (sleeves)—or even perforate liners if the process is left unchecked.

"Extended-life types continue to gain ground on fully formulated coolant.” -Dr. Frank Cook, Old World Industries

Diesel antifreeze is classified into two basic categories that have distinctly different additive chemistries: inorganic additive technology (IAT) and organic acid (or additive) technology (OAT), the latter usually identified as extended-life coolant, or ELC. A generally accepted third category—known as hybrids, hybrid OATs, or HOATs— includes formulations based on OAT chemistry, but containing one or more inorganic additives to enhance particular performance characteristics.

Notable among the ELC OAT hybrids are those containing the inorganic additive of nitrite, which has a proven track record in IAT formulations for deterring liner pitting by creating a tough oxide patina on the liner exterior. A nitrite-containing OAT often is identified as a NOAT.

“Each of these formulations—IAT, NOAT, and nitrite-free organic-acid technology coolants, or NF OATs—works exceeding well in the applications for which they’re recommended,” says Colin Dilley, Ph.D., vice president technology, Prestone. “Each of the technologies has its strengths and weaknesses; which one is best often will depend on vehicle mix, vehicle application, usage, and maintenance practices. To meet these varied applications, Prestone, as do most antifreeze suppliers, offers a full range of coolants under its Command brand.”

Until a couple of decades ago, the IAT type was the most widely used heavy-duty diesel antifreeze, routinely described as “fully formulated,” indicating that it has all the additives needed for heavy-duty applications and to distinguish it from “conventional” antifreeze, which is intended for light-duty applications and has no additives to prevent liner pitting. Virtually all IAT formulations use nitrite (sometimes with molybdate). The nitrite is used up as it protects liners from pitting, however, so the nitrite level requires frequent testing (with paper test strips or laboratory analysis), and the coolant must be treated with a supplemental-coolant-additive (SCA) package if levels are low.

Although fully formulated remains a viable product in certain applications, its use continues to diminish.

Coolant Resources

Coolant-maintenance Guidelines

Cavitation Causes and Cures

“Extended-life types continue to gain ground on fully formulated coolant,” says Dr. Frank Cook, chief technical officer, Old World Industries, a fluids-manufacturing company whose own antifreeze brands include Peak, Final Charge, and Fleet Charge. “I would guess that ELC as the original OEM [original equipment manufacturer] fill is 80 percent and fully formulated 20 percent. In the field, because of older trucks on the road, perhaps the aftermarket is greater than 20 percent fully formulated; but in general, ELC continues to grow.”

At Chevron, says Don Holdmeyer, industrial and coolants brand manager, Chevron Products Co., recent figures indicate that less than 10 percent of the company’s coolant volume is fully formulated—the remainder ELC.

Antifreeze based on “pure” OAT chemistry uses no nitrite, but instead, relies on an electrochemical process to deliver protection to spots on the liner vulnerable to cavitation-related pitting—and the process does not use up the responsible OAT additives. The overall additive package in OAT formulations depletes at a slow rate, and most ELCs claim a useful life of 12,000 hours or 600,000 miles—assuming proper maintenance.

Additives in OAT formulations are derived from neutralized versions of organic (carbon-containing) acids—such as the carboxylate acids of 2-ethyl hexanoic and/or sebacic.

“These formulations start with an acid,” says Shell’s Granger, “but are reacted with a base to form a carboxylate, or salt. The industry’s move away from fully formulated coolants to OAT coolants has been a big step, because it moved from a known technology with nitrite to a less-proven technology without nitrite. Supplementing core OAT chemistry with nitrite in some ELC formulations has helped ease the transition and provided some redundancy.”

Today, says Prestone’s Dilley, the move to nitrite-free coolants has a further impetus.

“The reason for eliminating nitrite [from OAT formulations] has to do with adverse chemical reactions that can occur when certain nitrite-containing formulations are used in cooling systems using aluminum components manufactured by the controlled-atmosphere-brazing process [CAB], which is becoming more prevalent as lighter-weight aluminum replaces brass in coolers.”

State of the market

Juan Rodriguez, marketing advisor, commercial vehicle lubricants, Americas, ExxonMobil, concisely sums up the state of today’s heavy-duty coolant industry.

“OEMs, as well as end users, are at different stages in the [coolant] technology evolution and often have varying requirements,” says Rodriguez. “As a result, coolant manufacturers must offer a range of products that provide solutions for these varied needs, and formulating coolants—and receiving OEM approval—can be challenging, with some OEMs having tests that are unique—  and that sometimes require years to evaluate.”

When submitting coolant samples to a laboratory, provide as much information as possible.Chevron’s Holdmeyer says that the company has more than a dozen different antifreeze formulations, some patented, others not.

“Some OEMs have specifications unique to various models in their product offering,” says Holdmeyer. “Most begin with ASTM D6210 [American Society for Testing and Materials standard for heavy-duty antifreeze] as a baseline, but many add specific testing requirements to ensure cooling-system protection. It’s complicated chemistry and can be a complicated process working with various OEMs and performing all the testing required to meet specifications.”

(For example, antifreeze meeting the Caterpillar EC-1 specification must be subjected to physical and chemical testing, evaluated for compatibility with other coolants, pass bench tests, and field-tested a minimum of 7,000 hours or 450,000 kilometers.)

Barnett Edelen, brand manager, antifreeze and coolants, Valvoline, says that the company has six retail Zerex products, as well as several more approved for specific OEMs.

“The antifreeze offering can cleave along OEM factory-fill lines, and also along retail-product lines,” says Edelen. “If you’re the supplier for factory-fill, then you’re responsible, along with the OEM, for warranty—so those products get tremendous scrutiny and extensive testing.”

Also adding to the overall mix of available antifreeze products, says Edelen, is an increased demand for ready-to-use coolants—50/50 mixtures of antifreeze and distilled/deionized water requiring no further dilution.

“For a long time,” says Edelen, “people didn’t want to pay for shipping water, but more users today are realizing that good-quality water can reduce deposits and that a ready-to-use product ensures proper freeze point. Using de-mineralized water takes out the hardness—calcium, magnesium—as well as corrosives, such as chlorides and sulfates. That’s difficult to do at home.”


Old World Industries’ Cook sums up.

“The process of formulating OEM-engineered and approved coolants is quite complicated, expensive, and time-consuming. It’s pretty much impossible for one antifreeze formula to meet every specification, because OEMs often have completely opposite requirements—for example, the requirement for nitrite, versus the requirement to be nitrite-free.”

Specifications for antifreeze used as factory-fill in Caterpillar and John Deere engines illustrate Cook’s point.

“No extended-life, nitrite-free coolants are officially approved by Caterpillar,” says John McConnell, market professional, parts and service marketing, Global Aftermarket Solutions. “For Cat diesel engines, Caterpillar recommends the use of Cat ELC coolant, which is an extended-life product that contains nitrite. Caterpillar recommends the use of nitrite, because of the added protection it provides against cylinder-liner cavitation.

“Caterpillar has seen an approximate 36-percent reduction in liner cavitation when nitrites are in the ELC formula. This added level of protection is a contributing factor to Caterpillar’s recommending a 12,000-hour/6-year change interval for Cat ELC. Caterpillar allows the use of other coolants in Cat engines when they meet the Cat EC-1 spec [which includes nitrites and molybdates], but recommends a shorter change interval of 3,000 hours or two years.”

At John Deere, says Mark Peckenschneider, product manager—bulk fluids, coolant, & DEF—John Deere Enterprise Parts Portfolio Team, all Deere engines are factory-filled with Cool-Gard II, which is nitrite-free, meets ASTM D6210, and is classified as a hybrid organic-acid-technology coolant.

“Cool-Gard II is formulated with additives to prevent liner damage from harmonic vibration,” says Peckenschneider. “Deere’s radiators are aluminum, and nitrites have an adversarial effect on aluminum. Nitrites work well with copper radiators.”

According to McConnell, Caterpillar has not found nitrite to be detrimental to aluminum components.

“What we have seen,” he says, “is that aluminum components that have not been properly ‘passivated’ [treated or coated to reduce chemical reactivity of surfaces] will tend to react with nitrites. [Although] coolant can potentially discolor, produce an ammonia-type odor, and deplete nitrites faster than normal, it will still perform as expected; Caterpillar has seen no detrimental performance issues when this occurs. Also, Caterpillar has a Coolant Conditioner Additive that can be used to passivate new aluminum components and eliminate the nitrite-depletion issue, allowing nitrites to enhance the cavitation protection of the ELC product.”

“The nitrite/nitrite-free debate continues,” says Cook, “and OEMs on both sides are confident in their positions on this matter—so most coolant suppliers offer both products.”

Nitrite or not

“The nitrite debate is causing a lot of confusion,” says Dr. David Turcotte, director, technology & product development, Valvoline. “In the effort to make vehicles more fuel-efficient, we’re making vehicles lighter by taking out cast iron and brass and replacing with aluminum. Nitrite can be tough on aluminum if you don’t maintain the concentration and have some other goodies in there to protect it; protecting aluminum is often better done without nitrite.

“In my opinion, non-nitrite coolants have gotten much better, nicely protecting against wet-sleeve cavitation and passing diesel-engine dynamometer pitting tests, like the ASTM D7583 John Deere test. The advantage [of non-nitrite coolants] is that additives do not deplete, as does nitrite, so they don’t have to be continually replenished. Heavy-duty engines might need nitrite protection, but OAT coolants are getting pretty close in performance.”

Shell’s Granger is a proponent of nitrite-free OAT formulations, but acknowledges that some OEMs and some end users aren’t convinced.

“What’s important in selecting antifreeze is to pick a flavor—a product that works in your application—then stick with it.” -Dr. David Turcotte, Valvoline

“We still have a lot of customers using the nitrite form,” says Granger, “but we’re working to convert them over to Shell Rotella ELC Nitrite Free by demonstrating that our technology provides the same type of protection as a nitrite coolant. Some OEMs, especially those with machines using very large engines, want proof that nitrite is not required. Some of these engines are so large, though, that testing has to be done in the field, which takes time. But that said, I haven’t seen any data indicating that nitrite-free coolant will not work even in these applications. It’s just a matter of getting the data.

“OAT nitrite-free chemistry is smart enough to go just where it’s needed, and it doesn’t put down all the deposits that would affect heat transfer. Plus, the lack of nitrite helps avoid problems with aluminum, the formation of ammonium, and increases in pH. In my opinion, it’s a ‘go-forward’ chemistry.”

Although Prestone’s Dilley acknowledges that some OEMs have moved to nitrite-free OAT coolants over concerns about aluminum coolers, he’s of the opinion that a well-formulated, nitrite-containing OAT (NOAT) will work in all systems—but adds a qualifier.

“There are, however, abundant bad NOATs in the market,” says Dilley, “so nitrite-free OATs are preferred. It’s the safer course. Also, many NOATS are not long-lasting, because the nitrite is consumed quickly. A well-formulated nitrite-free OAT can match or exceed the protection of NOAT formulations.”

On the maintenance side, Dilley advises users to know the exact coolant in use, saying that, although OAT and NOAT formulations are compatible, mixing the two dilutes the inhibitor package of each. Also, he says, making assumptions about coolant type by color can be misleading, citing recent instances of coolant being drained from trucks, because technicians interpreted the red color as indicating a NOAT, but saw no indication of nitrite on the test strip. What was drained, says Dilley, were perfectly good OAT formulations, also red in color, that never did have nitrite.

“Today, test strips have been developed that can evaluate a myriad of different parameters,” says Chevron’s Holdmeyer. “They are very useful field methods to evaluate nitrite levels, pH, reserve alkalinity, freeze point/boiling point—and even carboxylate levels in extended-life coolants.”

Old World Industries’ Cook adds a bit of a backstory about carboxylate-measuring test strips.

“The industry became so dependent on nitrite test strips for fully formulated coolants,” he says, “that not having a test strip to test nitrite-free OAT became a barrier to that coolant being used. After almost a decade, we developed a test strip that tests the amount of organic additive, and it works quite well.”

“On the nitrite debate,” says Valvoline’s Turcotte, “we’re not saying one or the other. What’s important in selecting antifreeze is to pick a flavor—a product that works in your application—then stick with it.”

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