Decreasing margins

Under most circumstances, a cooling system isn’t exchanging heat at its maximum possible rate; there is almost always some remaining capacity to handle an increased heat load. Old timers may recall the frequency with which some cars of the late 1950s overheated when the air conditioning was switched on—the increased load on the engine generated more heat than the cooling system could handle.

System designers and engineers attempt to build in an extra margin to handle a worst-case occurrence, but as modern vehicles present less underhood space for airflow, increased carrying capacities, and an ever-growing thermal load from forced induction, charge air cooling, bigger oil coolers and other systems, the safety margin is decreasing quickly.
Light vehicle engineers are watching this carefully, but the heavy duty and off road segments are on alert as they watch for problems. Large vehicles, particularly those operating off-road such as construction, mining or agricultural units, are at particular risk simply because they don’t move quickly enough to benefit from any large amount of ram-air through the coolers. In most cases, fans on these vehicles are running nearly all the time and the system may be working above 90 percent of its ability to exchange heat.

It’s easy to see then how a hotter than normal day or a slight restriction or blockage in the radiator fins could easily push a vehicle into an overheat. When that happens the unit is out of service, its job doesn’t get done and somebody is probably losing money.

The lesson here is that routine inspection and maintenance can sometimes be more important on the slow movers than on the road vehicles.

Inspection is simple: just look around before the unit is started. Any blockage in any of the coolers should be removed with either an air or water hose. If the coolers or radiators have air cowlings around the fan, make sure they’re in place and tight. Is the fan tight on its mount and the drive belt in good condition? Check the coolant level, too, on a cold engine.

Do you see any signs of seepage or leaking at hose joints?

Some problems are easy to see, but you have to look.

Credit:   Behr Hella Service

Maintenance should be based on both observed need and hours of use as recommended by the manufacturer. Replacing a worn part before it fails insures the vehicle remains in service. Maintaining the cooling system should also include periodic chemical tests of the liquid coolant using any of the variety of test strips or systems on the market.
These checks are particularly important if the engine requires a supplementary coolant additive (SCA) in addition to the anti-freeze chemicals. Many chemicals used in liquid coolants either wear out (deplete) or react with other elements over time. Failing to keep the proper mixture can lead to internal engine problems including corrosion and even plugging of passages.
As the reserve capacities of cooling systems get smaller, heads-up maintenance and common sense observation becomes an everyday necessity.


The Mobile Air Conditioning Society’s blog has been honored as the best business to business blog in the Automotive Aftermarket by the Automotive Communications Awards and the Car Care Council Women’s Board!

When having your mobile A/C system professionally serviced, insist on proper repair procedures and quality replacement parts. Insist on recovery and recycling so that refrigerant can be reused and not released into the atmosphere.

If you’re a service professional and not a MACS member yet, you should be, click here for more information.

You can E-mail us at or visit to find a Mobile Air Conditioning Society member repair shop in your area. Click here  to find out more about your car’s mobile A/C and engine cooling system.

The 33rd annual Mobile Air Conditioning Society (MACS) Worldwide Training Conference and Trade Show, Be the Best of the Best will take place February 7-9, 2013 at the Caribe Royale, Orlando, FL.


About macsworldwide

Mobile Air Conditioning Society (MACS) Worldwide Founded in 1981, MACS is the leading non-profit trade association for the mobile air conditioning, heating and engine cooling system segment of the automotive aftermarket. Since 1991, MACS has assisted more than 600,000 technicians to comply with the 1990 U.S. EPA Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment. The Mobile Air Conditioning Society (MACS) Worldwide’s mission is clear and focused--as the recognized global authority on mobile air conditioning and heat transfer industry issues.
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