Operational Considerations

The good news about the care and feeding of your intercooler itself is that not much is needed. Pared down to the basics, an intercooler is an air-to-air heat exchanger. According to Wayne Thomas of Pacific Oil Cooler Services, Inc.—one of the biggest repair stations that specializes in repair and overhaul of oil coolers and intercoolers—an intercooler doesn’t see the internal pressures oil coolers do and, accordingly, don’t usually wear out. He said that ordinarily intercoolers easily last to engine TBO, at which point they should be pulled, inspected and repaired as necessary.

Also, unlike oil coolers, some leakage is acceptable in intercoolers. Where there is zero tolerance for leakage in an oil cooler, finding a small air leak in an intercooler is not a yank-it-and-fix-it-now discovery. There’s time to evaluate the extent of the leak and whether it requires further action.

Thomas told us that there are two enemies of intercoolers. The more serious is corrosion—the bane of any aluminum aircraft component. The second concern is cracking due to vibration, although Thomas advised his company sees intercoolers sidelined by cracks far less often than from corrosion.

As with any part, an intercooler will eventually wear out, becoming unrepairable. At that point it’s time to either buy a new one or, better still, check to see if the outfit that developed your mod has come up with a more efficient version.

The more serious consideration, particularly on some of the older mods, is missing STC paperwork and POH supplements that establish manifold pressure limitations for climb and cruise that must be followed. If those limits are exceeded, the fact that the engine is getting substantially cooler air than it did during certification—especially on hot days—may result in the engine developing more than its rated horsepower. Doing so for any length of time means a significant risk of damaging the engine through detonation or overheating. On those systems in which the STC mandates reduced manifold pressure, the STC developer wasn’t kidding.

Some intercooler mods also include a cockpit gauge that the pilot references in setting manifold pressure. We’ve received word that it’s not unusual for those gauges to be inoperative. If you’re buying an airplane with an intercooler mod that includes a gauging system, make sure it’s working. If not, be suspicious of the engine condition.

In addition, some intercooler mods also mandate resetting the takeoff fuel flow to a new, higher level. Again, they’re not kidding—the engine needs it and failure to set it correctly is asking for problems.

Beyond wondering how the airplane got signed off on its last annual, we strongly recommend that a potential buyer not buy an intercooler-modified airplane that does not have full supporting STC paperwork. Expensive engine damage may already have occurred.

Recreating STC paperwork may range from merely expensive to impossible if the STC holder no longer exists.

Chuck McGill, principal of SafeFlight International, who gives specialized instruction in Cessna and Mooney aircraft, advised us that he regularly sees Cessna P210s with intercooler mods, no operating paperwork and mis-set takeoff fuel flows. That situation is often accompanied by a history of frequent cylinder replacement—something, he said, is not the case when the fuel flow is set right and the pilot knows how to set power correctly.

For airplanes that came out of the factory with intercoolers, such as the Cessna P210R, McGill, and others, told us that their experience is that the systems are well-designed and reliability is very good so long as operating procedures are followed.