What you should know about Charge Air Coolers

Turbochargers improve engine efficiency by compressing intake air. That generates heat. Unless compressed and constrained, warmer objects are less dense than cooler ones.In an engine, you want the air as dense as possible. Heat needed to ignite the fuel will be generated by compression. To keep air dense, we use charge air coolers (CACs). Found right behind the radiator, this heat exchanger cools charge air like a radiator cools coolant.CACs have plenum chambers on each side of the radiator, connected by cooling tubes, like a radiator's header tanks. Because they operate in an environment of extreme shock, vibration and temperature differential, they may occasionally need repair or replacement.

Basic maintenance consists of keeping airways clean and free of obstructions, minimizing corrosion, minimizing air loss, inspecting for proper mounting and inspecting for structural integrity.

Keeping airways clean

Since CACs are often mounted behind coolant radiators, small debris, such as insects, grass, plant matter and other foreign substances may pass through the radiator to collect on and block flow through the CAC. It is difficult to inspect the space between the two heat exchangers (radiator and CAC). The best way to clean the CAC is by removing it. Since this is not always practical, the best alternative is to use steam cleaning or power washing with hot water, in the reverse direction to the air flow.

Compressed air may blow debris back into the radiator. A flexible plastic shield between the exchangers will prevent clogging the radiator with debris from the CAC. If you use acid or caustic chemicals, flush everything thoroughly to remove all traces, or corrosion could result. Heat exchanger fins, necessary to increase surface area to more efficiently transfer heat, are easily bent or damaged. Damaged, the fins alter air flow, making the process less efficient. In other words, be careful.

Minimizing corrosion

Corrosion on metallic parts of CACs is usually due to exposure to road salt or sea water. At every PM interval (more often in winter in the "Ice Belt") clean all exposed heat exchangers with clean water. When fighting corrosion, there's no such thing as too clean.

Checking mountings

Shock and vibration are enemies of CACs. They loosen mounts, which increase their damaging effects. Rubber components, such as mounting isolators, grommets and shock mounts can deteriorate, weaken and break. They should be checked and replaced if necessary. Any signs of abrasion indicate relative motion between components. Nearby components should be checked for loose mountings, and any looseness should be corrected.

Checking structural integrity

At every PM interval, check CACs for cracks, breaks or bends in: the mounting frame; gussets; side members; the plenums; mounting brackets; stay rods; other components. As indicated in The Maintenance Council Recommended Practice RP333, ("Heat Exchanger Exterior Maintenance and Cleaning,") "replacing a cracked part before it breaks can save the time and expense associated with an actual in-service failure."TMC also has an RP on "Charge Air Cooler Integrity," RP331. It lists the average life expectancy of CACs as five years or 700,000 miles. That is an average, so while yours may last a million miles or more, it also may fail at 400,000 to 500,000. The RP speaks to manufacturers and OEMs, listing considerations truck operators find important. Truck operators must do their share, because, as the RP states, the "design life expectancy is based on the premise that proper maintenance practices of the intake system (internal and external) will be performed at intervals specified by truck manufacturers. Coolers that are subject to abuse, mishandling, improper maintenance, or operated in an abnormal or abusive environment, will experience a resultant loss of expected service life."Air loss within allowable limits specified by the truck OEM is to be expected, but excessive air loss is not. Leaks occur at inlet and outlet tubing-to-hose connections as well as within cores. Normal leakage is usually around 5 psi within 15 seconds, at 25 psi boost.When cleaning CACs, as opposed to radiators or other heat exchangers, special precautions must be taken. Whenever CACs are removed or hoses are disconnected from CACs, care must be taken to prevent any dust or debris from entering the CAC or the intake. Whenever the system is opened, damp, lint-free shop rags should be secured over all openings, both at hose ends and on the cooler. When replaced, all debris should be cleaned from the cooler/hose interface.

If you do have to replace a cooler, be sure it is the equivalent of the old CAC with respect to air capacity and flow, as well as mounting hardware and location.  -by Paul Abelson

The information in this article is from the Recommended Practices Manual developed by TMC members and published by The Maintenance Council.You can obtain a copy by calling 703-838-1763.

Paul Abelson serves Land Line as technical editor and freelances from his office in Lisle, IL.

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