1. Check the radiator for dirt and debris. Restricted airflow through the front of the radiator will reduce its ability to cool the vehicle’s engine. Most foreign matter can be cleared away from the radiator’s fins with a hose – remember to spray the water from inside the engine compartment outward to loosen and flush debris away from the radiator – or with compressed air. Be careful when flushing the core or scrubbing the fins with either water or compressed air as the fins are very delicate and can bend or break easily.

2. Visually inspect cooling system hoses. In addition to absorbing the vibration that is transmitted from the engine to the radiator, the hoses carry coolant to and from the radiator. Without flexible rubber hoses, the vibration may break off the inlet or outlet connections of the radiator. Check the hoses for bulges, cuts or scrapes. When the hose(s) are cool, feel along the length of them for soft spots. Aging and under-hood temperatures cause the hoses to harden and lose their flexibility. At this point, the hoses no longer absorb vibration, but rather, they transmit it.

3. Make sure to also tighten all hose clamps, and always replace worn hose clamps. White- or rust-colored deposits at the clamps indicate a leak. Do not over-tighten clamps, but rather, tighten them until the hose just starts to bulge. Then, run the engine to operating temperature and retighten the clamps. To avoid cold-water leaks, clamps should be retightened after a run-in period of one hour to one week.

4. The average life expectancy of a belt is three years. They should be inspected for glazing, cracking or deterioration, as well as to determine if they’re loose. Replace any belt that is glazed, cracked or split, greasy, or peeling.

5.. A visual inspection of the radiator could reveal several possible problems, including coolant leaks (coolant stains on the core are an indication of a leak). Fin deterioration is a condition prevalent in areas where road salt is frequently used. In addition, if your vehicles operate close to salt water your fleet is susceptible to fin deterioration. The salt also has an adverse effect on the radiator tubes. A cracked header and/or header tanks are usually the result of metal fatigue due to continued high stress. Also, a visual inspection of the truck’s radiator might reveal a loose mounting bracket caused by excessive vibration. A defective head gasket, pressure cap, or thermostat may cause a blown seam between a tank and header.

6. A breakdown of the metallic composition of a truck’s radiator occurs over time as a result of the chemical reaction between the coolant and the metal. This will result in the build-up of white powdery deposits that can block flow of coolant through the radiator core. Eventually the truck’s engine will overheat because it has to work harder to pump coolant through the system. As little as a 10 per cent restriction in a heavy-duty system’s radiator can cause serious damage to the vehicle’s engine. Signs of this type of chemical reaction should be noted immediately, and the truck’s coolant should be tested.

7. How regularly should you test the antifreeze in a truck’s cooling system? That depends on a variety of factors, including driving and weather conditions. As a general rule the coolant level should be one to two inches below the radiator filler neck when cool. Use an antifreeze tester to determine the protection range of the coolant. It should be at least adequate for the geographic area where you operate your fleet of trucks. If the coolant is over two years old, is discolored or is rusty, flush the system and refill it with new antifreeze solution. The two-year replacement interval is necessary to maintain proper rust inhibitor and other additive protection in the cooling system.

8. The coolant/water ratio is another important factor in a regular maintenance program. When ethylene glycol is mixed with water, it has a much lower surface tension than water alone. This allows the coolant to flow through high temperature areas without turning to vapor or steam. The coolant molecule has the ability to “trap” or absorb heat. When straight anti-freeze is used the molecules are not separated and therefore cannot carry away excess heat. By diluting with water to a 50/50 mix, the water sustains the molecule allowing it to carry away excess heat.

9. Electrolysis is caused when stray electrical current finds its way into the coolant in search of ground. This can result in small pinhole leaks in the metal tubes and tanks on heater cores and radiators. Part of any fleet’s cooling system maintenance program should include a regular check for stray voltage. Inhibitors can be introduced into the cooling system to combat both electrolysis and corrosion of the radiator components.

10. Pressure test the system, starting with the radiator pressure cap. Examine the cap gasket and replace it if it’s torn or cracked, or if the rubber seal is dried out. Using a pressure tester, apply pressure equal to one pound p.s.i. above the rated pressure of the cap. If the cap does not reach or hold the pressure, wash the cap again and repeat the test. If the cap still does not reach or retain the pressure, replace it. You’ll most likely have to change the cap on regular intervals of every 200,000 – 250,00 miles.

11. Check the thermostat by inserting a suitable thermometer into the radiator neck and running the engine. When the coolant level drops in the radiator, the thermostat has opened and is allowing circulation. Record the temperature on the thermometer and compare to the thermostat specifications. It should be no more than a few degrees either way of the actual thermostat setting. If you are not in the correct range, replace the thermostat.

12. The charge air cooler is frequently overlooked. Charge air coolers are found in every heavy-duty application because they’re absolutely essential to meeting emission regulations. In addition, they also improve power density, lower fuel consumption and reduce the thermal stresses on the engine by cooling the turbocharged air before it enters the engine. Accumulations of debris in the finned areas of a charge air cooler, which must handle massive amounts of air, could damage the cooler. If there’s a buildup of debris in any section of the cooler, that section overheats and torsional stresses develop in the charge cooler core. The core exterior can be cleaned with a stiff bristle brush. It isn’t necessary to clean the inside of the charge air cooler as routine maintenance, only if there’s a specific reason such as a turbocharger failure in which oil may have been thrown into the cooler.

The National Automotive Radiator Service Association (NARSA), a worldwide trade association with more than 1,500 member businesses, was formed in 1954 as a forum for communication and education within the automotive cooling system aftermarket. The association provides its members with the latest technical information so they can provide you with the best cooling system service. Additionally, NARSA strives to provide education on the proper servicing and repair of the cooling systems of today’s automotive fleet. For more information on NARSA, NARSA membership, cooling systems or member shops, call 800/551-3232 or visit the association’s web site at www.narsa.org.