Tackling Today’s Tough Coolant Questions

May 9, 2011

The best advice for maintaining heavy-duty-diesel cooling systems has not changed: 1) follow the engine/vehicle manufacturer’s antifreeze recommendation; 2) use deionized water to dilute antifreeze in typically a 50/50 ratio; 3) always top-off the radiator with this mixture; and 4) follow the antifreeze maker’s recommendations for testing and maintenance.

The best advice for maintaining heavy-duty-diesel cooling systems has not changed: 1) follow the engine/vehicle manufacturer’s antifreeze recommendation; 2) use deionized water to dilute antifreeze in typically a 50/50 ratio; 3) always top-off the radiator with this mixture; and 4) follow the antifreeze maker’s recommendations for testing and maintenance.

Construction Equipment asked several coolant specialists to address questions about maintaining today’s heavy-duty-diesel cooling systems and about today’s changing antifreeze formulations. They’ll speak for themselves, but a quick review of the basics might be helpful to place their comments in context.

As you might already know, antifreeze types can be classified into three basic categories: 1) inorganic-acid technology (IAT); 2) organic-acid technology (OAT); and 3) OAT variations—often called hybrids, hybrid-OATs, or HOATs.

The most widely used antifreeze is “fully formulated,” which uses an additive package consisting of  inorganic compounds. An essential additive is nitrite (sometimes accompanied by molybdate), because it forms a cavitation-resistant film on wet cylinder liners. (Cavitation is pitting of the liner’s surface, caused by vapor bubbles that violently implode against the liner as it vibrates with the diesel’s combustion cycle. Left unchecked, this process can breach the liner and allow coolant into the engine in as little as 30,000 miles.)

OAT-type antifreeze, often called “extended-life coolant” (ELC), uses additives made from neutralized versions of organic (carbon-containing) acids—often, but not always—the carboxylate acids of 2-ethyl hexanoic and/or sebacic. Hybrids result when an OAT antifreeze also contains certain inorganic additives used in fully formulated—such as nitrite, silicate or phosphate. A nitrite-containing OAT, for instance, is a NOAT. (Some would say, however, that a true hybrid is an antifreeze based on non-typical organic-acid chemistry.)

Fully formulated coolant must be periodically checked with chemically sensitive paper test strips that indicate freeze point (glycol content), nitrite (or nitrite/molybdate) levels, and, in some instances, pH. If make-up additives are required, a supplemental coolant additive (SCA) package is used. (Or, you could send a coolant sample to a fluids-analysis lab, along with the oil sample.)

Additives in an OAT coolant deplete at a much slower rate than those in fully formulated antifreeze, but extended-life antifreeze is not maintenance-free. It  should be checked regularly for contamination and freeze point. An “extender” additive package usually is required at the mid-point of the coolant’s life.

A debate in the industry at present is whether OAT formulations need nitrite to provide adequate cavitation protection. Many OAT antifreezes have routinely used nitrite since their introduction, and many continue to do so.  Today, however, a few truck and equipment makers have caused a stir in the industry by using a nitrite-free OAT as factory fill.

Expert opinions

Realizing that users of heavy-duty diesels have practical questions about coolant usage and maintenance, Construction Equipment passed along a list of such questions to a number of coolant specialists. Among those who responded were Dr. David Turcotte, technical director, Valvoline; Sean “Marty” Martinelli, regional sales manager, Penray Power Fleet; and Stede Granger, OEM technical services manager, Shell Global Solutions.

Construction Equipment: Can a well-maintained fully formulated coolant last indefinitely—that is, approaching the hours/miles of service claimed for “extended-life coolants” based on OAT formulations?

Turcotte: If one uses a fully formulated coolant and a reasonable re-inhibition strategy that includes proper top off, the coolant may never need to be changed. Too much is made of the non-depleting nature of organic acids, given the protection they offer is modest under cavitating conditions.

Martinelli: Penray’s Fill-for-Life program is intended to extend the coolant’s life to overhaul. This program entails using a fully formulated coolant meeting TMC RP 329 A, TMC RP 330 A, or ASTM D6210 standards. Type A indicates a borate/nitrite chemistry. Other chemistries containing nitrite/molybdate/phosphate can require flushing at about 250,000 miles due to solids. We recommend maintaining the coolant with a Penray Need Release coolant filter, which releases additives into the coolant as its chemistry changes.

Granger: We believe you reach a point where the fully formulated should be drained, because as additives deplete, they drop out of solution and build up. Also, oxidation products are forming, making the coolant acidic. The continual addition of additives also may eventually affect water pump life. Our recommendation is to drain the fully formulated at a shorter interval than ELC. If we wanted to be really rigorous, we’d do coolant testing, then make a call. When in doubt, go with the manufacturer’s recommendation.

CE: Does the quality of SCA packages for fully formulated coolant vary? How does a user know that a particular product is of good quality?

Turcotte: Many quality levels exist. Choose products specified by the engine/equipment manufacturer. Without first-hand experience, you are playing Russian Roulette with your expensive equipment.

Martinelli: Generally, a good SCA will contain a coolant stabilizer, such as Stabilaid, and meet specifications of TMC RP 328.

Granger:  Conventional fully formulated coolants may vary significantly in the type and amount of inorganic inhibitors and the amount of silicate stabilization.  Again, we recommend following the engine / equipment manufacturer’s recommendations and using good quality suppliers and coolants meeting the OEM specifications.   

CE:  There seems to be a number of OAT formulations. How do these differ?

Turcotte: The term “hybrid” is typically used to describe a variety of chemistries that follow the simple philosophy that says: “Let’s use the best ingredients to make the coolant.” We shouldn’t get caught up in what the fluid does not contain or whether it’s an OAT, IAT, NOAT, p-OAT, m-OAT, and so forth. The issue is: Does the fluid protect in my application? To find out, look at the manufacturer’s recommendation, and don’t think for a minute that “universal” coolants work.

Granger: There is a wide variety of OAT chemistry that may be utilized in coolant formulations, such as aliphatic monoacids (straight chain molecules with one acid group), aliphatic diacids (straight chain molecules with two acid groups), and aromatic monoacids (ring- shaped molecules with one acid group). The key thing is that the coolant is formulated with an optimum amount of OAT to meet the OEM’s performance requirements.  

CE: Seems to be a debate about the need to use nitrite and/or molybdate in OAT antifreeze formulations. What are the arguments?

Martinelli: Generally, nitrite and molybdate are the only industry proven formulations to protect against cavitation. Some believe that the carboxylates themselves can provide adequate  cavitation protection. This again would be contingent upon maintaining the carboxylate coolant within contamination/dilution maximums.

Turcotte: To obtain good protection of solder, molybdenum is very useful.  OATs can be very aggressive on solder.  Only nitrite or nitrite plus molybdate can protect diesel engines that truly cavitate. Actually, about a third of diesels don’t cavitate, and any coolant will work. Another third cavitate, but the problem can be stopped with nitrite. Also, OAT formulations will slow it down in these engines for a reasonable life. The last third are the more powerful, hot and/or loosely built diesels. These pit no matter what you do. Nitrite/molybdate can slow it down and provide reasonable service life.

Granger: There is substantially more aluminum in some of today’s engines and cooling systems—coolant passages, water pumps, filter modules, intercoolers, radiators and heater cores. Under certain conditions, for example, when flow rates are high, we’re seeing that nitrite reacts with aluminum and starts a corrosion process that forms an ammonia gas, which raises the pH, places aluminum in the coolant, and causes the nitrite level to drop. There’s a developing trend toward the use of ELC coolants without nitrite.

CE: What’s the layman’s explanation of how a fully formulated coolant with nitrite protects cylinder liners from cavitation, versus how a non-nitrited OAT coolant provides protection?

Martinelli: Basically, nitrite provides a protective microscopic film on the coolant side of the liner. This transforms ferric oxide (rust), which is very soft, into Fe3O5, which is very hard. Carboxylates are believed to form a chemical bond at vulnerable sites, creating a mono-layer coating.

Turcotte: Nitrite is a fast-acting surface-filming additive. It rebuilds the protective oxide film on the cast-iron surface immediately after an imploding bubble has blasted the oxide off the base metal. The repair prevents corrosion or cylinder-liner pitting. OAT slowly builds up a protective layer on the metal surface. If the layer can withstand the bubble implosions, no pitting will be observed. If the protective layer can’t take the physical damage, the metal surface will pit, and we will see that OAT can’t repair the damage on the time frame of the corrosion event. If  it’s a gunfight, nitrite is fast on the draw and OAT has no chance.

Granger: Nitrite essentially provides a protective film by converting iron oxide from hematite (Fe2O3) to magnetite (Fe3O4), which is harder and prevents pitting.  Since this reaction is irreversible, nitrite must be continuously replenished. With ELC (OAT) coolants, the carboxylate acid (RCOO-) in the OAT reacts with iron (Fe++) on the surface to provide a protective film of iron carboxylate (Fe(RCOO)2). Since this reaction is reversible, the OAT attaches only when needed with free iron ions and may provide protection for 600,000 miles or longer in a well maintained system. OAT coolants have demonstrated satisfactory protection of wet sleeve cylinder liners in the newly established ASTM D7583 John Deere Cavitation Test and are currently being used widely in heavy-duty diesel engines in Europe and Asia-Pacific, where nitrite is prohibited.

CE: If a fully formulated antifreeze is mixed with an OAT-type coolant, or vice versa, how should the coolant be maintained going forward?

Martinelli: Fully formulated antifreeze can be mixed with an OAT coolant, as long as you maintain it with an SCA going forward. You can’t mix anything with an ELC more than the manufacturer’s recommendations, usually 10 to 25 percent, and continue to use it as an ELC.

Turcotte: It is possible to dilute one technology with the other and not have enough of either to work. Given the cost of engines and cooling systems used today, if you contaminate the system by mixing coolant, man up and drop the fluid. Put the proper OEM-recommended fluid back in and try to do better maintenance going forward.

Granger: What we typically say is that an ELC can be contaminated with up to 15 or 20 percent with conventional coolant with no worry. Above 20 percent, the coolant should be checked to determine that OAT additives are present in sufficient quantities to maintain protection. Shell will soon release a simple new system, called Test Tool, that will quickly determine if the OAT level is acceptable. If the level is not acceptable, the user can maintain the system as a fully formulated coolant, use a conversion fluid to convert it back to ELC, or simply drain and refill.

CE: Can cooling systems be converted from one technology to another without draining the existing coolant—assuming it is in good condition?

Martinelli: Our current process is to drain 30 percent of the OAT, HOAT, or NOAT and add one pint of Pencool for every four gallons of coolant capacity. Top-off with a fully formulated coolant meeting TMC RP329, TMC RP 330, or ASTM D 6210 standards. For conversion to an ELC, it would be best to drain and flush the unit, fill with an ELC coolant, and maintain it contaminate free.

Turcotte: It is important to follow the manufacturer’s guidelines when changing coolant. If the manufacturer allows for different coolant technologies, it is almost certain that one will want to drain the old fluid and replace with the proper new fluid. There’s no free lunch.

Granger: Shell’s conversion fluid is designed to convert fully formulated coolant systems over to an ELC system. The conversion kit comes with everything necessary for the user to first determine if the existing coolant is good enough to keep, and also with a sample bottle that is sent to the lab to make sure the conversion was successful.

CE: Do OAT formulations allow better heat transfer within an engine?

Martinelli:  Not really. The idea is to keep the heat transfer fluid (water) clean. Any system that becomes corrosive from poor maintenance (either ELC or fully-formulated), or uses poor-quality water, will build up scale, which leads to poor heat transfer and coolant passage plugging.

Turcotte: Properly formulated coolants in a wide variety of chemistries can promote clean and well-protected heat transfer surfaces and good heat rejection. All coolant technology contains trade-offs and benefits.  There is no universal, supreme chemistry that is all things to all engines and to all cooling systems.

Granger: The difference between ELC coolants and fully formulated is that ELC lays down no additive film on engine surfaces—what mechanical engineers call a “fouling factor.” Even these thin additive films can be significant in impeding heat transfer. As the engine ages, the fouling factor increases with conventional coolants, but not with an ELC system. Dynamic heat-transfer testing published in the literature shows that ELC coolants may provide significantly lower temperatures and greater heat transfer compared to conventional fully formulated coolants. Therefore, we believe heat transfer is significantly better with ELC coolants.

CE: Any other concerns/debates going on these days in the diesel-coolant world? 

Turcotte: The heat load from EGR systems and modern high-powered engines demands proper cooling-system maintenance regardless of coolant-additive technology.  Keep the cooling system full, top off with the proper fluid, make sure the system pressurizes and is in working order as the vehicle ages.  Regularly inspect the fan, hoses, belts, clamps and system connections. Long-life coolant is a terrible thing if it makes people forget the needed routine maintenance by creating a false sense of security.

Martinelli: The key to a good coolant program is to choose a coolant technology and maintenance product that works for your application. New emissions standards have increased coolant temperatures and the demand on the system dramatically. It’s crucial for a fleet to have a good program in place.

Granger:  The changing views on the importance of nitrite in heavy-duty coolant is an important issue today. The use of nitrite is a mind-set, but maybe it’s time to change. We’re seeing fleets pleased with the results of using nitrite-free ELCs, and see no reason to change back. The industry continues to look into different ways of doing things better in the long run.