A heavy duty truck’s cooling system is primarily designed to prevent the engine from overheating. Secondary tasks are to provide heat to the cab and, in some cases, the trailer. Today, cooling systems also integrate with various elements of a diesel truck’s aftertreatment emissions system.

That is a lot of responsibility, which is why fleets should take responsibility for emphasizing cooling system management in the shop. Inattentiveness by technicians and drivers could open the door to things like coolant contamination, corrosion, leaks, and component failures.

Heavy duty vehicles and engines have changed over the years, forcing fleets to further rethink the coolants they use and overall level of attentiveness to cooling system maintenance.

“Today’s modern vehicles have protection needs that have become more complex,” says Virginia Whittington-Byrd, technical manager, product development at Valvoline. “Engines are running hotter. Radiators and engines are constructed using aluminum and non-metallic materials. Cooling systems have very little copper, brass, and solder. There have even been advances in gasket and seal materials used in the cooling system, resulting in more complex coolant technology.”

“There is also so much more being cooled today, such as water-cooled alternators and turbos,” adds Clay Parks, vice president of strategic development at Bar’s Leaks, a maker of leak repair products for heavy duty trucks. “In the future, we’ll see more batteries and fuel cells that will also need to be cooled.”

In the present, a diesel truck’s cooling system is already working hand-in-hand with the aftertreatment system. For instance, engine coolant is used to warm up and thaw diesel exhaust fluid (DEF) in cold climates. The emissions equipment is put at risk if the truck’s engine isn’t running in tip-top condition, so the cooling system is vital to both.

Any liquid, including coolant, that makes its way into an exhaust stream can foul the diesel particulate filter (DPF) and lead to premature plugging. A truck could also end up with damage to other aftertreatment components including the diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) system.

Exhaust gas recirculation (EGR) has created another potential issue. An EGR cooler exchanges heat from the exhaust to the engine coolant. An EGR cooler failure can cause a coolant leak in the exhaust that can ultimately reach the aftertreatment system — potentially harming vital system components.

Preventive maintenance and addressing leaks

Cooling systems are relatively straightforward, yet a host of problems can arise from one end of the system to the other. Key components like water pumps, radiators, and fans can fail. Leaks can occur almost anywhere, commonly caused by blown head gaskets, corrosion, and damaged hoses and connections.

Technicians should regularly inspect the coolant level in the reservoir as part of a regularly scheduled coolant preventive maintenance (PM) program.

“Fleets are often very good at managing engine oil PM practices, such as taking oil samples and conducting engine oil analysis,” says Lawrence Wong, product technical specialist for Chevron Lubricants. “But fleets don’t always focus on coolants. It’s a good idea to check a vehicle’s coolants every time it receives a regular PM on engine oil. A routine check on the coolants, which includes a check of the pH levels along with using a refractometer to check the freeze point, will help ensure that both are within acceptable limits. If they are not, this may be an indication that something else may be off. Then a technician will need to pull a sample and perform additional analysis and adjust as required.”

Wong says it is also a good idea to pressure-test the coolant system to ensure that the radiator pressure cap is functioning properly.

“Also check with your lubrication supplier on coolant testing kits they might be able to provide,” Wong adds. “For example, Chevron has a dedicated Cool Tools kit for maintaining coolant.”

Visually inspecting for leaks is something that cannot be neglected. Technicians and drivers should religiously check for puddles beneath the truck, as well as wet areas around all cooling system hoses and connections.

Another sign of a leak is if the cooling system does not pressurize.

“That could mean a pressure cap needs to be replaced, a hose clamp is having an issue, a gasket has failed, or corrosion damage has occurred,” Valvoline’s Whittington-Byrd says.

“From the radiator and heater core to the core plugs in the block, there are a lot of opportunities for an external coolant leak,” Bar’s Leaks’ Parks reminds. “That said, the more dangerous leaks are typically the internal leaks that a technician cannot see. These types of leaks, where coolant gets into the oil, can really cause some damage to the engine.”

Unless a fleet regularly samples engine oil for analysis, an issue like that could go undetected for some time. As a preventive measure, technicians can utilize a cooling system treatment that seals leaks.

For instance, Professional DiFM Cooling System Treatment from Bar’s Leaks helps lubricate and seal internal, external, and coolant-to-oil leaks. The company says these 5-gram tablets also help inhibit the formation of rust and scale, and overall help keep the cooling system clean. The tablets can be an effective defense against hairline cracks and mild corrosion damage.

Avoiding coolant cross-contamination

Much like the engines they are tasked with cooling, coolants themselves have changed in recent years. There are three essential ingredients fleets should look for.

“The coolant we use is typically a 50/50 mixture of ethylene glycol and water,” says Stede Granger, OEM technical services manager for Shell Lubricants. “The ethylene glycol helps prevent freezing and raises the boiling point. Water is necessary because it is much more effective at heat transfer. By keeping it 50/50, we get a combination of good heat transfer and effective freeze protection down to roughly minus 34 degrees Fahrenheit.”

With today’s engines, coolant cross-contamination has become another potential danger to watch out for. That is why Granger says the third coolant ingredient, the additive that prevents corrosion, has become the most important ingredient.

After a 42-year career, Granger recently retired at the end of 2020. He says that most modern heavy duty trucks now have aluminum heat exchangers. It is also common to see aluminum heater cores. Historically, diesel engines were almost entirely cast iron with copper brass radiators and heat exchangers. Thus, aluminum-nitrite corrosion had not been a concern — until now.

“We are now making changes in our coolant recommendations,” Granger says. “In the past, we used nitrite in heavy duty coolants to protect cylinder liners from pitting. Now with all of the aluminum components, we’re seeing more aluminum-nitrite reactions. We now encourage fleets to use extended-life coolants with additive technology, such as Shell Rotella ELC NF that can protect cylinder liners without the use of nitrites.”

Granger says a handful of OEMs are still using coolants with nitrites for factory fill. However, it’s only a matter of time before they also switch to a nitrite-free, extended-life coolant.

Granger’s shoes at Shell Lubricants are being filled by Brad Jordan, a 26-year industry veteran himself. Jordan says it is not ideal for a fleet to stock more than one type of coolant. Similar to stocking multiple engine oils, multiple coolants add complexity and cost to a fleet maintenance operation. Fleets need more storage and dispensing tools, additional labeling, and more technician training and oversight.

Stocking multiple coolants can be even riskier than stocking multiple engine oils. With engine oil, the product is completely drained and replaced. That is not the case with coolants. With coolants, a technician or driver is usually topping off whatever is already in the system. The chances for cross-contamination are greater.

“Whenever you’re stocking more than one coolant, there is always the chance for a mix-up,” Jordan says. “Different extended-life coolants often use different additive chemistries. If you mix two coolants together, you are diluting the additive chemistry — likely to the point that it is no longer as effective as you need it to be.”

“You have to be really careful when you mix chemistries,” Granger adds. “We have defined that there should be at least 80 percent of our additive in the coolant. If the right level of additive is not there, the coolant can’t do its job.”

When selecting a coolant to use, Valvoline’s Whittington-Byrd says fleets must first understand OEM requirements. Then, consider warranty implications and expected service lifetimes.

“It’s important to note that a coolant can be ‘approved,’ ‘meet or exceed,’ or be ‘recommended’ for the application,” Whittington-Byrd explains. “It is always best to use an ‘approved’ coolant, which means the coolant has been approved by the OEM with extensive testing. When an ‘approved’ coolant cannot be sourced, the next option is a coolant that ‘meets the specification.’ That means the coolant has been comprehensively tested to perform properly.”

Regardless, maintaining the right additive level is critical these days. That is why Shell offers Rotella ELC Correction Fluid, which helps fleets restore proper additive levels if their Shell Rotella ELC Nitrite Free coolant becomes diluted with other coolant chemistries. Additionally, Shell has partnered with Acustrip to provide Rotella ELC NF-calibrated test strips to help technicians identify when the additive level is deficient in a given vehicle’s coolant system.

For instance, if a vehicle was accidentally topped off with a different coolant, a technician could test that vehicle’s coolant “cocktail” with a test strip. The test strip will indicate additive concentration by color. If the test indicates that the additive level is low, the technician can pour some correction fluid in and test again until it is back over 80 percent.

“Don’t worry, a technician is very unlikely to add too much additive and cause damage,” Jordan points out. “We always say that a little too much additive is better than not enough.”

In some circumstances, Granger says it is a good idea to test the coolant whenever a vehicle finds its way to a service bay for routine service. This is especially the case when the technician is not sure where the truck has been, or what coolant may have been used to top off.

On the other hand, in properly maintained cooling systems, Granger says minimal testing is required. Using the right coolant — reinforced by rigorous inspection and preventive maintenance practices — can help keep a cooling system operating effectively for many years. In today’s trucking industry, that bodes well for not only the engine, but also the aftertreatment system.