How Good Are Long-Life Coolants?

Light & Medium Truck, Feb 2006 by Galligan, Jim

Use of extended life coolants has been growing for years, and higher exhaust temperatures expected with some of the new diesel engines next year should cement their use in the medium and heavy truck market. Here's a look at some of the pluses and minuses with the longer-life coolants.

If you are not using extended life coolants for your diesel engines today, you may tomorrow. Extended life coolant is the broad name for the latest glycol-based engine coolant formulas, although "latest" is a relative term here. ELCs have been on the market for about a decade and, in fact, dominate the over-the-road commercial truck market. According to a study done for Shell Lubricants by MacKay & Co., an Illinois-based consulting firm, ELCs had 82.7% of the Classes 6,7 and 8 commercial truck coolant market in 2004 compared with 16.8% for conventional coolants. Other coolant formulas had the remaining 0.5%. According to the same study, there was a slight drop in use in Classes 6 and 7, but not much. ELCs were used in 81% of Class 7 trucks and 76% of Class 6 trucks in 2004.

Suppliers say that the ELC's superior heat-handling and metal-protecting properties, as well as its durability, gives it an edge over conventional coolants in low-emission diesel engines, using exhaust gas recirculation.

The next generation of low-emission engines, due out next January, are expected to generate more heat than today's models.

How much of an increase may be different in each engine, said engine and coolant spokesmen, but those engines with higher heat will put greater demand on the coolant and the cooling system. Some engine suppliers are saying that today's conventional coolants can still do the job, but the capabilities of ELCs might make them a better choice in some others.

Conventional and extended life coolants both use ethylene or propylene glycol as a base, and both provide antifreeze protection. But suppliers say ELCs outperform conventional coolants in the way they fight corrosion and carry away heat.

Ron Moser, coolant business manager with Chevron Corp., explained that most glycol-based conventional engine coolants use silicates and other inhibitors to form a chemical layer over the metal in order to prevent corrosion. While that layer does a nice job of protecting the metal from pitting and corrosion, it also holds in heat, a potential issue for some of the 2007 engines, which may need to throw off that heat more effectively.

"Traditional coolants lay down a layer of silicates and inorganic solids on the system and protect the surface from having oxygen hit it. That shuts down corrosion," said Moser. "[Extended life formulas] use carboxylate inhibitors, which protect differently than traditional coolants. Carboxylates stay in solution until there is an active (bare metal) site in the engine. They shut down corrosion by forming a very hard layer over that site. Think of corrosion like a fire. It needs oxygen and fuel, in this case, metal. Conventional coolants block the oxygen from hitting the metal surface, but the layer traps heat. Carboxylates attack the fuel, the metal areas where corrosion becomes active. They pacify the chemical reactions and form an oxide layer that shuts down corrosion."

Supplemental coolant additives must be added to conventional coolants to extend their inherent corrosion-fighting capabilities. As most technicians and fleet maintenance managers know, the SCAs deteriorate over time and have to be replenished. That leads to another difference - durability, perhaps ELC's biggest marketing point.

The current crop of ELCs are developed with organic components that do not lose their anti-corrosion capabilities as rapidly as conventional coolants and, thus, do not require periodic additions of SCAs.

"The carboxylates, the organic acids that are used in ELCs, do not break down as rapidly as conventional coolants," said Dan Arcy, technical marketing manager with Shell Lubricants. "Because there's slower depletion in the coolant, you can go out as far as up to 600,00 miles [without a coolant change]. Typical conventional coolants need to add inhibitors along the way, perhaps every 12,000 to 20,000 miles."

Initial ELC fills typically last for 300,000 miles and can be extended to 600,000 miles with an ELC extender in Class 8 over-the-road trucks. Of course, only some medium-duty trucks will hit 300,000 miles. The Technology & Maintenance Council of American Trucking Associations defines an extended service interval coolant as one that can go beyond 100,000 miles in on-highway use, or six months in stop-and-go, pickup and delivery operations, without having to replace depleted chemicals.

Cost Comparison

Extended life coolants may cost roughly twice as much - or more - than a conventional coolant per gallon. Given that many light and medium trucks may take a decade to hit that 300,000 mile mark noted above, will ELCs pay for themselves in lower mileage operations?

Fleets have to run the numbers themselves, but since ELCs do not require the regular addition of supplemental coolant additives or periodic flushes, the trade-off in maintenance costs savings could be significant for some fleets.