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Modern Trucking Techniques
Cooling system investigation
Cooling system problems can rob your truck of critical heat management. Cooling system investigation can catch these culprits before any real damage is done.

By Paul Abelson
senior technical editor


Mention engine heat today and the reaction is far different from what it was years ago.

Heat wasn’t nearly as big a problem before the October 2002-compliant engines hit the scene. With the literal meltdown that many engines suffered because of the higher temperatures, cooling system maintenance is much more critical now than it was back in the day.

But staying on top of cooling system maintenance doesn’t mean you have to bring in a highly

trained team of pros. In fact, with a little work and effort, you can become your own cooling system investigator and troubleshoot plenty of cooling system problems.

The cooling scene

Much as crime scene investigators do, the best way to find the culprit robbing you of heat management in your cooling system is to track the process systematically from start to finish. Just follow it through the engine and out the exhaust system.

Some of the heat takes the direct route, as hot exhaust flows directly through the exhaust manifold, into the mufflers or the diesel particulate filter and out to the ambient air. As the gas flows, it heats the parts it contacts, and that heat is dissipated into the surrounding air.

Far more complex is the remaining heat. It flows through cylinder heads and cylinder liners into liquid coolant that is pumped through hoses to a radiator. Along the way, a temperature valve, the thermostat, regulates coolant flow to the radiator.

The radiator absorbs heat from the coolant and transfers it to thin metal fins. They transfer it to air flowing over the fins. If there isn’t enough air forced in by the vehicle’s speed, a fan turns on, which sucks air through the radiator and blows the air into the engine compartment.

In post-October 2002 engines, some of the hot exhaust is diverted to an exhaust gas recirculation cooler, often referred to as an EGR cooler. The gas is then metered back into the engine. The cooler removes heat from the gas by transferring it to the engine coolant. That adds to the radiator’s load.

When we follow the heat flow, we find the following components or supplies are involved in the process. Each requires inspection, testing or regular maintenance.

The culprits

As you conduct your own cooling system investigation, watch for a number of problems that can reduce effectiveness. Identifying these culprits is essential to rectifying the problems.

Cylinder liners can pit. Coolant can lose its chemical charge. Hoses can harden and crack or soften and collapse. Hose clamps can loosen. The thermostat can go out of adjustment. Hose


There are a lot of how-tos in the Technology & Maintenance Council’s Recommended Practices. In fact, nine separate RPs deal with cooling system repair and maintenance alone.

You can start your maintenance with RP313C, the Checklist for Cooling System Maintenance.

You can learn how to test your thermostat for proper operations as well as how to check fan temperature controls from the RPs. Inspection and Maintenance of Accessory Belt Drive Systems is another RP you might be interested in checking out.

Other maintenance tips for cleaning heat exchangers are in RP333A, Heat Exchanger Exterior Maintenance and Cleaning.

Recommended Practices are available for purchase individually from TMC by calling (703) 838-1763. But, for less than the cost of the nine RPs relating to cooling systems and accessories, you can join TMC as an owner-operator member. Your membership includes the complete TMC RP manual, either in print or on CD. Owner-operator members can serve on TMC Task Forces that create the RPs, or they can comment on RPs that go out for ballot.

fittings on the radiator can crack. The water pump blades can erode, and its gasket can crack and leak.

The radiator can clog. Fins can corrode or break off. The core can leak where it is joined to the tank. The fan drive can go out of adjustment. Drive belts can crack and fray, and grooves can deteriorate. Sensors or connectors can corrode, sending false signals to controllers.

Don’t feel overwhelmed

Cooling system maintenance should start with an inspection of coolant level and freeze protection. Then test for the concentration of supplemented coolant additives – dubbed SCAs for short. Some extended life coolants or long life coolants do not require SCA treatment unless diluted with traditional coolants. SCAs protect cylinder liners from pitting.

Test for hard water in your system. If you have to replace coolant, use a system cleaner first. Minerals in hard water form scales that impede heat transfer. Remove your thermostat and test it for proper operating temperature.

   Visually inspect fans and shrouds at every preventive maintenance interval or more often. Also look at fan hubs and blades. Make sure drive belts are in good condition and pulleys are in proper alignment and in good condition.

Check radiators for leaking. Make sure radiator caps hold and release pressure as specified in your engine owner’s manual. Be wary of counterfeit radiator caps and caps that are off-spec.

Visually inspect charge-air coolers and air conditioner condensers, and listen for telltale sounds of air leakage. Check hose clamps and fittings.

Check the condition of hoses. If they feel hard and brittle, they will soon crack and leak. They have been exposed to heat and ozone. Soft, mushy feeling hoses have been attacked internally by chemicals. They may soon collapse, cutting off coolant flow.

Heat exchangers can become clogged with bugs, leaves and other debris. Fins can be bent. All heat exchangers – radiators, charge-air coolers, oil coolers and air conditioner condensers – should be carefully cleaned. Water pumps should be inspected according to engine makers’ instructions. LL


Paul Abelson may be reached at