Air support

| December 12, 2008

For best fuel economy and minimal engine stress, make sure your charge air cooler system is a lean, clean breathing machine. Here’s how.

Rules governing nitrogen oxide and soot are tougher than ever. One of the most critical tools for compliance is the air-to-air charge air cooler system, or ATAAC.

The system uses outside air to cool intake air. Since outside air is cooler than engine coolant, a properly designed ATAAC can cool an engine’s intake air much more effectively than earlier systems.

The charge air cooler is important because as the turbo compresses the air, the air heats up. Hot air has a negative effect on combustion. The charge air cooler cools the compressed air almost back down to outside temperature before it goes into the engine.

“This permits a more dense charge of air to be delivered to the engine, resulting in improved engine performance, fuel economy, and lower emissions,” says Gene Walker, Detroit Diesel’s national service manager.

The cooler’s thin tubes and fins are designed to eliminate maximum heat within a lightweight component. The cooler is highly efficient, but the small spaces between the fins easily can become clogged with dirt, and its thin metal walls – operating under pressures greater than 50 psi – can develop leaks.

Ductwork transfers the air from the turbocharger outlet to the cooler and then to the intake manifold, Walker says. Flexible rubber couplings and hose clamps secure the ductwork to the turbocharger, the cooler and the manifold. Flexibility is key in accommodating the movement between engine and chassis and in minimizing vibration.

“If the charge air cooler’s condition is deteriorating, the engine will eventually overheat,” says Mike Powers, product development manager for Caterpillar. “We’ve found that for every degree intake temperature increases, exhaust temperature is likely to increase 3 degrees.”

While the cooler’s function on the newest Caterpillar engines is no different from that on competing engines that use exhaust gas recirculation, engines with Cat’s ACERT technology run higher boost pressures and could develop problems more quickly if the ATAAC is off kilter, Powers says.

These three areas are key to cooler preventive maintenance:

CLEANING. The biggest ATAAC maintenance issue is cleanliness. “If plugged up with dirt, you get almost the same effect as when they leak: less airflow,” Powers says. When airflow is blocked, the warmer air is not as dense as properly cooled air, even though it’s been compressed by the turbo.

“Proper inspection and maintenance of the components is required to ensure continued efficiency of the CAC,” Walker says. “Damage to CAC and ductwork requires immediate repairs. CAC leaks can possibly be found visually, while small leaks will have to be found using a pressure leak test.”

Volvo’s operator manual warns about reduced airflow from accumulation of dirt and insects between the fins of the radiator, air conditioning condenser and charge air cooler. “This increases the load on the fan and air conditioning compressor and can result in engine overheating and other performance-related problems, such as high fuel consumption,” the manual says.

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