Keep Cool: Engine coolants have evolved, so have maintenance needs

by Eric Berard

Coolant formulas have changed — and so have related maintenance practices.

MONTREAL, Que. — Internal combustion engines burn fuel to produce kinetic energy, and generate heat in the process. That’s why we’ve always needed coolants – although, they’ve evolved from simple well water into modern-day mixtures of glycol and water.

The fundamental role has never changed. Its job involves keeping the engine from overheating and parts from seizing. The glycol raises the water’s boiling point and lowers the freezing point.

They key to balancing the two opposing missions is maintaining the right proportions of water and glycol, which is 50/50 under most conditions. At this concentration, the mixtures prevent freezing down to -37 C and withstand heat up to 129 C, says Colin Dilley, Prestone’s vice-president of technology.

That’s the theory, anyway. Life on the road is harsh. Coolant levels can be lower than intended because of evaporation and leaks. Any air pockets prevent the fluids from circulating as they should, creating unwanted “hot spots” that create a downward spiral, he says. Overheating degrades additives in the glycol, causing the mixture to become more acidic. This leads to the by-products of corrosion, generating more heat.

“It’s a pretty destructive cycle,” Dilley says, noting how hot spots around the engine head will cause gaskets to overheat and deteriorate.

A simple way to keep air from contaminating the coolant involves making sure the radiator cap’s seal and spring are working properly. Attention to that simple part, sold for under $20, can protect against a complete engine overhaul.

Checking for leaks and testing system pressure is the key here, says Greg Braziunas, Daimler Trucks North America’s manager – transmission, clutch, fluids and test planning.

And that pressure should be around 15 psi, adds Dan Holdmeyer, Chevron’s industrial sector manager.

Beware of cocktails

Yet coolant leaks can still happen. Maintenance teams or drivers may need to top off the cooling system once in awhile.

That task, however, can be more complicated than it appears.

For instance, conventional coolant should never be mixed with an extended life formula, says Carl Hergart, Paccar Technical Centers’ director of powertrain and advanced engineering. “Each coolant formulation uses a different balance of additives, so two halves [of different coolants] do not make a whole.”

Mixed conventional and extended life coolants actually keep each other from realizing their full potential.

“You’re getting two completely different technologies to protect the cooling system, neither one of which are at a concentration to fully protect that cooling system,” says Dilley. And he says the mistake is frequently made because color codes that once applied to the formulas don’t always work anymore.

A conventional coolant used to be green and an extended life type would be purple, red or yellow, depending on the type of additive — silicate, a nitrite organic acid technology (OAT), or nitrite-free OAT. “There’s significant confusion out there now, and each fluid comes in multiple colors with multiple labels and multiple caps, and it is not easy at all for people to understand what type of coolant that they are using,” the Prestone representative adds.

Maintain your concentration

Topping off the coolant with pure glycol – or just water – will also distort the ever-important 50/50 glycol-water concentration. That’s not a bad thing, per se, but you need to be aware of the strengths and weaknesses of each change in concentration.

Water transfers heat better than glycol, so people operating in very hot climates may prefer a mixture of 60% water and 40% glycol, while in the extreme cold a formula of 60% glycol and 40% water may be adequate because glycol resists freezing better than water. But glycol carries the additives which protect the engine from corrosion and other threats, so any shift from a 50/50 mixture will create some form of compromise.

In the vast majority of cases, the best thing is to stick to the 50/50 rule, says Heather DeBaun, Navistar’s technical specialist – engine oils and coolants. “It’s not a standard practice to modify your concentration between summer and winter months,” she says.

Paccar’s Carl Hergart agrees: “Typically the same fluid is used year-round, since coolant remains in a vehicle for an extended period.”

One way to keep that 50/50 balance is to top off with premixed coolant, and ensure the coolant meets the ASTM D6210 standard, DeBaun adds.

Premixed coolants also have the advantage of containing quality-controlled water, she notes.

Maintenance teams who still prefer to make their own mix should make sure they use only de-ionized or distilled water, says Chevron’s Holdmeyer, because tap water is inconsistent from one area to the other and can cause scale to build up in the system.

“Using tap water in your cooling system will end up eventually causing some plating of some deposits, calcium or whatever else is in there. That’s why we like deionized or distilled water,” he says. Conventional coolants with phosphates are even more susceptible to hard water conditions, causing deposits.

Monitoring and troubleshooting

Cooling systems will require their own preventive maintenance as additives slowly deplete over time. Personnel that we spoke to all agree that the manufacturer’s recommendations should be observed when it comes to drain intervals, which can actually vary by application for the same engine model.

Since coolants stay in trucks for so long – sometimes more than 1.5 million km – that regular monitoring is needed to ensure they continue to work as designed.

Tested coolant samples can offer telling details. If a lab detects metal particles, for example, the water pump might be wearing out, Holdmeyer says.

Daimler’s Braziunas clearly advocates the value of lab tests, but notes how test strips capable of measuring the additive levels in OAT coolants are a viable option when there’s no lab nearby.

In terms of preventive maintenance, Navistar’s DeBaun recommends using a refractometer to test the coolant’s freeze point twice a year. “That’s something that many shops have today. It’s pretty easy. You put a drop of coolant on the refractometer window and you hold the refractometer up to the light and it basically will tell you what the freeze point is,” she says.

Though a hydrometer, a refractometer will provide more accurate results, Holdmeyer adds. The hydrometer offers a range of concentration, whereas a refractometer can be calibrated at zero with a drop of clean water and then used to identify concentrations within 1% or 2%.

Your own senses can also tell that something’s gone wrong, according to Prestone’s Dilley. A fishy or ammonia-like smell can reveal degrading coolant, he notes.

Also, look for signs of discoloration. “Make sure it’s not turning brown, which could be an indication of rust in the cooling system, or it might be an indication of oil leak. Or if it’s turning brown, it could be an indication that you’re overheating it and burning it,” says Holdmeyer.

If the fluid is cloudy, if it appears that there’s some sort of contamination, “that would be a time that you would want to consider draining and refilling,” DeBaun says.

Materials and building methods

The construction of today’s radiators, including such things as controlled atmosphere brazing (CAB) and different materials, can also influence coolant life.

Aluminum is the most commonly cited newcomer. “Newer engines – including the cooling system – have more aluminum components, which are more susceptible to heat stress, corrosion, electrolysis and erosion,” DTNA’s Braziunas says.

The white metal in cooling systems also generates chemical reactions of its own. “Coolants that worked well in the cast iron/copper brass system do not necessarily work well in cast iron/aluminum systems,” Dilley says.

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