Cooling System Maintenance Considerations for Fleet Managers

Automotive engineers have made great strides in recent years in their attempts to increase the efficiency of engines. Their efforts, unfortunately, cause them to butt heads with various principles of physics. As good as they are, today’s gasoline engines are usually less than one-third efficient. Diesels do a bit better with efficiencies running generally just over a third. With the exception of post-combustion heat recovery systems, that leaves approximately two-thirds of the heat energy either going out the tailpipe or being handled by the cooling system.

Thermodynamics says that any heat engine will run more efficiently as its operating temperature increases, but, of course, there’s a limit since parts will start to melt. Engines are designed to operate efficiently within a relatively narrow heat range. Too cool means less power output. Too hot means overheating problems. Keeping the operating temperature in that narrow heat range is the job of the cooling system.

Producing an efficient cooling system is the job of automotive design engineers. Keeping the system operating efficiently is the job of a fleet’s maintenance department.

Ethylene glycol, propylene glycol or long-life/extended-life coolant should be used in cooling systems year-round as the glycol provides both freeze and boil-over protection. It also provides a stable environment for gaskets and hoses, which might leak if only water is used as a coolant. Antifreeze products offered by reputable manufacturers will comply with applicable ASTM standards and should be used only with distilled water in a blend of between 40 percent and 60 percent. A 50 percent blend is ideal.

Coolant containing too high a concentration of antifreeze can cause silicate dropout and water pump leakage. A study of water pump failures by Cummins ( found an overconcentration of antifreeze in 78 percent of the pumps they examined.

Because magnesium and calcium found in most tap water can cause scaling on internal cooling system components, tap water should not be used in cooling systems. In addition, sulfates in tap water can corrode these parts. Distilled water should always be used when filling a cooling system to help avoid these problems.

Engineers at Baldwin Filters ( outline the various functions required of an engine coolant:
• Removes heat
• Lubricates components such as water pumps
• Provides freeze protection
• Prevents scale and sludge formation
• Protects against corrosion

The first three can be handled by a simple mix of a low-silicate antifreeze and distilled water. Supplemental coolant additives (SCAs) must be introduced to the system to prevent scale and sludge formation and to provide corrosion protection. SCAs typically contain inhibitors designed to prevent generalized corrosion and cavitation erosion, and they keep hard water scale from depositing on engine surfaces and use buffers to reduce the acidity of the coolant.

Fleets need an effective preventive maintenance program to keep the cooling system clean. Because this can be labor intensive, it’s too often not done. All commercial trucks should be equipped with coolant filters, and fleet managers should strongly consider working with cleaning filters that are used for a relatively short time instead of normal coolant filters. Manufacturers have developed spin-on cleaner/filter cartridges that chemically clean the system while the truck is used in normal operations. These units are left on the truck for a few weeks. After that, the coolant is checked with test strips to ensure that dissolved solids are within OEM-recommended levels. The cleaner/filter contains the chemistry needed to clean a cooling system as well as what’s needed to protect it against further corrosion.

Check for Leaks
In many cases a small coolant leak might not be noticed because of the high temperatures under the hood during operation. The leaked coolant simply evaporates as the truck travels down the road. The result could be an automatic shutdown.

The best way to check a cooling system for small leaks is to pressurize it before making an inspection. Too often, fleets that pressurize cooling systems on a regular basis only pressurize to cap pressure. System pressures up to 18 psi should be used.

Arctic Fox ( makes a tool called a Coolant Dam Pressure Tester that uses shop air to quickly pressurize systems up to 18 psi. After pressurizing the system, the technician lets the truck sit for a while and then looks for problems. After checking for leaks, he or she can use the same test unit to check the cap.

High-quality silicone coolant hoses and heater hoses are found on most commercial trucks today, yet cold water leaks are still a problem faced by the trucking industry. To obtain good sealing at the coolant hose connection, the entire system – stem, hose and clamp – must be considered. Constant tension or spring-loaded clamps generally seal better than constant diameter screw clamps, especially for sealing in low temperatures. These generally work better because they contract as the material in the hose wall thermally contracts and loses resilience.

Cooling systems require maintenance on a regular basis. Antifreeze needs additives. Systems need to be cleaned and checked for leaks. When cooling systems are working properly, most engine problems can be avoided.

About the Author: Tom Gelinas is a U.S. Army veteran who spent nearly a decade as a physicist before joining Irving-Cloud Publishing Co. While at Irving-Cloud, he worked in various editorial capacities for several trade publications including Fleet Equipment, Heavy Duty Equipment Maintenance and Transport Technology Today. Gelinas is a founding member of Truck Writers of North America, a professional association, and a contributing writer for Utility Fleet Professional.

Fleet Maintenance, Management

Tom Gelinas

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