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.

PM: COOLER
“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.

Suggested cleaning steps include using air pressure or a water stream from the back of the core. Air pressure should not exceed 30 psi for radiator and cooler cores. A fin comb also is suggested for loosening debris.

Cleaning should be handled gently, Walker says, to avoid damaging the delicate cooler. Detroit Diesel recommends letting its mechanics handle cleaning tasks.

Detroit’s operator’s guide calls for checking the cooler every 30,000 miles and inspecting the hoses and piping every 15,000 miles.

The Mack manual recommends daily inspection of the front area or grille and a firm bristle brush and soapy water to remove all bugs, leaves and dirt.

CONNECTIONS. The Mack manual recommends checking all air ducts and gasket connections and torquing hose clamps to 45 to 55 lb.-in. every 15,000 to 25,000 miles, depending on the severity of service.

Every 60,000 to 100,000 miles, the cooler mounting bolts should be torqued to 30 lb.-ft., and the welds joining the side tanks to the cooler heat exchanger core should be inspected for cracks.

Many of the latest spring-loaded hose clamps do not require torquing after installation. Check your manual. Make sure cooler mounts are kept snug to minimize vibration and related damage.

LEAKS. If engine performance falters because of a suspected lack of air, check for a possible small leak in the cooler core or tank welds. Disconnect and remove the cooler and have it tested. A competent truck or engine dealer can pressurize the unit and determine whether the internal pressure drops. The unit then can be repaired or replaced if needed.

PM: HOSES
You’d expect cooler hoses to be like radiator hoses, a maintenance item, but that’s not the case. “We don’t expect them to fail,” says Steve Egleston, heavy truck lead engineer at FlexFab. “They are expected to live far beyond the warranty period,” even with extended warranties, he says. If not damaged by anything external, the hoses may last a million miles.

“The normal failure mode would be some sort of abrasive wear to the exterior,” Egleston says.

There’s no need to replace cooler hoses at some arbitrary mileage, but Egleston says the maintenance-conscious owner-operator should periodically inspect the cooler hoses for these things.

SURFACE DAMAGE. First gently clean the hoses with a damp cloth to see the surfaces better. “Look to make sure that nothing is damaging the system’s hoses,” he says. “Look for nicks and cuts. If the hoses are functioning properly, and the damage has not progressed past the outside layer, the hose is OK.”

CONTACT WEAR. Also make sure that nothing on the truck, such as wiring or other hoses, is touching the cooler hoses. Securely tie any items away from the cooler.

“You should keep an eye where the support rings and hose clamps bear against the outside of the hose,” Egleston says. “If you see white textile material, you could develop a leak. This kind of wear reduces the strength of the hose and could lead to complete failure.”

PROPER CLAMPING. Also make sure the clamps are installed straight, Egleston says. The proper clamping angle is important because once a leak starts, heat isn’t transferred away from the hose the way it should be, and the hose may overheat. Make sure the clamps are torqued to the manufacturer’s recommendation.

“We expect the clamp to remain at initial torque because the rubber underneath will get a compression set,” Egleston says, explaining that the rubber will compress only so far.

LEAKS. You should also walk around the truck with the engine idling and listen for turbulent, high pressure air that sounds like a hiss or roar, Egleston says. If you hear a possible leak, ask a friend to accelerate the engine, which will boost pressure and make such a problem easier to detect.

INTERIOR WEAR. If the hoses are removed for any kind of repair, Egleston suggests inspecting them carefully inside and out. Check the liner for chalky deposits that would indicate overheating. In case the hose material has adhered to the connection, clean the connection thoroughly before installing the new hose, as the residue would interfere with proper sealing.

Egleston advises OEM replacements. “When it comes to reliability, you can’t afford anything less,” he says. “We and our competitors realized before 2002 that the temperatures and pressures these hoses were subjected to meant we had to take a step up in terms of quality of construction.”

A poor-quality hose may become chalky and hard, causing it to blow off under a stressful run. That will leave you limping home under low power.

PM: FAN
While ram air normally keeps the CAC and radiator cool at highway speeds, the engine-driven fan becomes critical in traffic and especially when climbing steep hills at low speeds. Monitor these components to ensure optimal fan operation:

SHROUD. Periodically inspect the fan shroud to make sure it forms an evenly spaced cowling around the fan that will channel the airflow. Replace missing mounting bolts, tighten loose ones and replace the shroud if damaged or cracked.

BLADES Inspect the outer edges of the fan blades for cracks or wear caused by rubbing the shroud. Some shroud-to-fan contact problems may be caused by worn engine mounts. If you suspect trouble, get your engine dealer to inspect the engine and transmission mounting.

BELTS. Make sure the fan drive belts are snugly tensioned. Their surfaces should have the slightly rough appearance of their unworn cloth cover.

Serpentine drive belts should have teeth that show only negligible wear and an intact cover with no cracks. The belt tensioner should be angled so its indicator is between the two lines behind it on the block. Rotate the tensioner away from the belt and then release it. If there is obvious friction as it restores tension, replace it.

CLUTCH. Monitor the fan’s operation. You’ll note that it normally comes on at a certain operating temperature, slightly above the point where the engine thermostat opens.

If fan clutch engagement is delayed or the clutch is slipping, you may notice reduced performance in newer engines or smoke in older engines only when climbing a steep grade at lower speeds.

Rebuild the fan clutch if it is slipping. If engagement is delayed or inconsistent, repair the relevant switches and wiring.

Following these steps should go a long way toward ensuring your engine gets a continued, adequate supply of properly cooled air. The results will be minimal engine stress and emissions, and maximum performance and fuel economy.


AIR COOLER SYSTEM TROUBLE

SYMPTOMS

  • High levels of soot in the oil, revealed by rapid, obvious thickening or darkening, or oil analysis.

  • Older engines: smoke with slightly reduced power.
  • Newer engines: significantly reduced power, especially obvious on hills.
  • Increased fuel consumption.
  • Higher than normal exhaust temperature, as indicated by pyrometer readings.
  • High-pitched squeal caused by an air leak in the charge air cooler or high pressure hoses and piping.
  • Warmer than normal engine operating temperature.
  • A loud pop while driving, especially when climbing hills, followed by a great reduction in power, suggests a disconnected or blown charge air cooler hose.

CAUSES

  • Dirt or dust on fin or tube surfaces, or partial clogging of those passages.

  • Poor airflow because of inconsistent fan clutch operation, fan or shroud damage, or a slipping belt.
  • Leaks in tubes, ducts, hoses or their joints, or in piping.
  • Leaks in the cooler itself may occur because of parts separation at a joint, or a crack. Often accompanied by noise.
  • A clogged air cleaner.
  • Poor turbo performance.
  • Wastegate malfunction.
  • Improper valve lash (especially intake) settings.

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