Kings of Cool

| April 07, 2005

Penray Fill-For-Life 2-way test strips are dipped in the coolant and then compared with the scales on this chart. The upper scale determines coolant concentration while the lower scale determines nitrite (SCA) concentration.

If you can’t stand the heat in your engine, get out of the cab – and check your radiator.

Getting the heat out of the engine block requires a good water pump and clean coolant, but that is only half the battle. The other half is throwing all that heat off to the outside air. This is the job of the radiator, and EGR engines and the aerodynamic, sloped noses of many late-model trucks are making that job tougher and tougher.

The radiator consists of upper and lower tanks linked by dozens of thin-walled, narrow metal tubes with coolant flowing down through them. This exposes the coolant to metal in contact with outside air so it can get rid of heat (radiate) from the engine.

There isn’t much room for the radiator in an aerodynamic truck so the tubes have flat sides to help put the maximum amount of metal into a small space. Their narrow shape also keeps the coolant moving very fast inside the tubes, throwing heat off more efficiently. Closely spaced metal fins run between the tubes. This increases the total metal surface in contact with air, throwing off still more heat. But packing all this metal into a small space makes the outside of the radiator subject to clogging with debris.

Having wet cylinder liners in direct contact with the coolant in a diesel improves performance, but it makes the cooling system a high-maintenance item. Trace amounts of exhaust gas leak around the liner seals and make the coolant corrosive. The result can be cooling system deposits and clogging in the radiator. Because the radiator tubes are so narrow, the deposits can easily clog those tubes shut.

The radiator operates under pressure produced by the radiator cap. The cap holds the coolant in until the pressure exceeds 7 psi to 15 psi and then relieves the pressure to avoid bursting any system parts.

The pressure raises the boiling point of the coolant well past the normal level of 212 degrees Fahrenheit. The higher boiling point enables the radiator to throw off a lot more heat than it could without pressure. The pressure also helps keep the block and cylinder liners cool by keeping steam bubbles, which interfere with cooling, from forming.

Air Flow

The radiator can’t do its job without lots of outside air flowing through it. Larry Erickson, field service manager at Peterbilt Motors, says the narrow openings between fins and tubes will definitely pick up some “road debris that will restrict airflow.”

Gary Falendysz, senior principal engineer in the truck division of Modine Manufacturing, says periodic cleaning of the air side of the radiator, charge air cooler, condenser and other heat exchangers is essential. “In order for these heat exchangers to work properly they need airflow,” Falendysz says. “Leaves, bugs and other road debris can foul them, restrict the airflow and reduce performance.”

The outsides of tubes and fins should be cleaned at least twice a year unless you operate in very dusty areas – then it should be done more often. Falendysz suggests doing this whenever the vehicle is washed.

The Mack maintenance manual says, “Using compressed air or water spray, clean insects, leaves and other foreign matter from radiator core openings as required. Always clean the radiator core from the engine side. Never use a wire or a screwdriver” to pry out leaves or dirt.

Erickson says the best, safest way to clean the fins and tubes is with a pressure washer that you can regulate, using warm water. “If you use 200 psi, it will bend the fins,” Erikson says.
On many trucks air shields direct air through the radiator. These shields should be checked regularly for cracks. Keep the belts that drive your fan in good condition and at proper tension. Also investigate and fix any problems with the clutch fan to help keep the radiator functioning when you’re operating in traffic or climbing hills.

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