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Can the Antifreeze in Your Bus Fleet Handle the Big Chill?

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This year has seen all kinds of weather extremes all across the nation, and as we move into the heart of winter, there are likely to be record cold temperatures if this trend continues. Now is the time to check your cooling system to make sure it’s fully charged and ready, especially if you operate a school bus fleet and have the opportunity to get caught up over the holiday break.

Advances in cooling system technology and coolant chemistry have made it possible for engine manufacturers to greatly extend service intervals, and in some cases, eliminate the use of coolant filters. Most Cummins MidRange engines have been operating successfully without coolant filters for the past decade.

This article outlines a few quick and easy maintenance and service tips that bus fleets can follow to ensure long-term reliability and durability of their engines.

Hardware: Cooling system hardware itself doesn’t require much in terms of maintenance. Other than checking hoses and seals, one important element to be aware of is the radiator cap. Cummins engines come with a 15 PSI radiator cap, which helps to manage the boiling point of the coolant inside your engine. This is a higher pressure than prior years, so if you need to replace a cap, make sure your replacement is up to the task.

Fluids: The key chemical in antifreeze/coolant is either ethylene glycol or propylene glycol. The first offers better protection against freezing or boil-overs, and is suitable for all climates, but it is toxic and must be handled (and disposed of) properly. Propylene glycol offers slightly better protection against issues such as liner pitting, solder bloom and corrosion, but will increase in viscosity at low temperatures, so it is not recommended for extreme cold weather applications. While less toxic, it is still considered hazardous waste.

Types of Coolants: There are three basic types of coolants – conventional, organic and hybrid. Conventional coolants contain nitrites and molybdate with mostly inorganic additives and are the lowest-cost option with the shortest service intervals. Organic Acid Technology (OAT) coolants offer the longest service intervals, and do not contain nitrites or molybdate. Hybrid coolants are a blend of the two.

As seen below, different formulations of coolant each have a distinct color, helping to ensure that your technicians are using the correct matching coolant when topping off your radiator. It is always a good idea when doing top offs or complete flush-and-fill procedures for your customers to use the same type of coolant that the manufacturer or OEM used as factory fill. If there’s a question, your customers should refer to their Operations and Maintenance manual for guidance. Many newer buses that do not have coolant filters recommend that only OAT coolant be used.

Fleetguard® ES Compleat™ is the best choice for optimum performance, but your maintenance team can use any coolant that meets the CES14603 standard.

Fluid Testing: The cooling systems on Cummins heavy-duty and medium-duty engines are designed for easy checkups and maintenance. Typically, when a vehicle is brought in for an oil change, it’s a good idea to double-check the coolant fluid level (it can evaporate over time, even in a closed system) and top off, if necessary. Technicians should also check the acidity (pH), sulfates and chloride of the coolant using a test strip such as the Cummins Quick-Chek CC2718. Bus fleets running conventional or hybrid coolants will then need to check the strength of the nitrites and molybdates (OAT coolants don’t have these) using test kit CC2602. These tests can be completed in two minutes and provide accurate visual confirmation that the coolant has the right chemical composition to do its job./p>

The third and most important test for this time of year is a check of the freeze point, which can be performed with either test strips, a hydrometer or a refractometer. Cummins recommends the use of a refractometer because it is more accurate and eliminates potential issues due to variation in color perception.

Action Steps: If the cooling system in one or more of your buses does not pass the tests, here are the corrective actions that need to be taken:


  • If the coolant level is low, add more coolant. Cummins recommends a premixed solution to ensure demineralized water.
  • If the coolant package is inadequate (chlorides, sulfates or pH levels are off), a flush and fill should be performed.
  • If the additive level is low, use of a supplemental coolant additive (SCA) will be indicated, and the system should be retested to make sure adequate protection is provided.
  • If there is a clogged filter or other evidence of contamination in the system, a complete draining, cleaning, flush and fill should be performed and the filter replaced.

Fleetguard® Compleat ES is the best choice for optimum performance, but your maintenance team can use any coolant that meets the CES 14603 standard.

If you use a concentrate and add your own water, you should always perform a water-quality test, as hard water with excess amounts of calcium and magnesium salts can impede heat transfer and result in head cracking and oil degradation, while high chloride levels can cause corrosion issues. A “best practice” is to always use demineralized or deionized water.

Specific testing requirements and mileage/hourly recommendations for extended service intervals for cooling systems on Cummins engines are outlined in QuickServe® Online (QSOL) at Section 3 – Extended Service Intervals, Table 3, Fleetguard Recommended Coolants and Section 6 – Coolant Testing.

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