To TBO and Beyond ...

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Eleven tips for operating your piston engine to attain maximum longevity and minimum maintenance expense along the way to major overhaul.

  1. Don't let your engine rust!

    • Fly frequently. Try not to allow the aircraft to go more than a week or two without flying. Merely running up the engine on the ramp actually does more harm than good. Turning the prop through by hand doesn't help, either.You need to get your oil temperature up to 200 F or more to boil off the condensation, and you can only accomplish that by flying the airplane.

    • Hangar your aircraft. Whatever it costs, it's worth every penny. Protecting the paint, windows, and upholstery is just about the least important reason for hangaring an airplane! The real benefit of hangaring is protection of the airframe and engine against internal corrosion, and protection of fuel bladders, hoses, and other rubber and plastic parts from deterioration.

    • Pick your oil carefully. If your airplane sometimes sits unflown for weeks at a time, you might do better using single-weight oil like Shell 100W or 80W instead. Single-weight oil provides much longer-lasting corrosion protection than a multigrade oil like 15W-50 or AV-1 because it is molasses-thick at room temperature. If you operate in cold climates, consider using multigrade in winter and single-weight the rest of the year.

  2. Keep your engine clean inside.

    • Keep your induction air filter in good shape. Consider using a Brackett foam filter and replacing it at least annually.

    • Check your alternate air door regularly. If it isn't sealing tight or is sucking open, your engine is breathing dirty unfiltered air.

    • Install a spin-on full-flow oil filter if your engine is not already so equipped. It will pay for itself very quickly. An oil screen is simply not enough.

    • Use spectrographic oil analysis. Take an oil sample at every oil change and send it to the lab. If silicon is more than 10 ppm, you have a dirt problem.

  3. Never cold-start without a preheat.

    • How cold is cold? There is no magic temperature. Any start with the engine temperature at or below 32 F should be considered abusive. Starting at or below 20 F should be a capital crime.

    • Oil pressure is not the issue! Using multigrade oil in wintertime, lubrication isn't really an issue even at subzero temperatures. Cold-starts damage your engine because the pistons heat up much faster than the cylinders do, temporarily reducing piston-to-cylinder clearances to the point where metal-to-metal contact is unavoidable.

    • Preheating is easy. Tanis heaters are simply wonderful. In above-zero temperatures, a couple of 100W shop lights and a blanket can keep engine temperature 40 F above OAT. When away from home, paying for a night in a heated hangar is worth every penny.

  4. Avoid unnecessary thermal cycles.

    • Hours don't wear engines out...thermal cycles do! If your engine ran 24-hours-a-day in a test cell at cruise power, it would probably go 6,000 hours between overhauls. The reason our engines don't last nearly that long is because we start them up and shut them down and heat them up and cool them down every time we fly (and sometimes when we don't).

    • Try not to start your engine unless you intend to fly. Don't taxi your airplane from the hangar to the radio shop—tow it. Don't stop at the fuel island before taxiing to parking—call for the fuel truck. Whenever you start your engine, imagine that you just tossed a $20 bill out the storm window.

    • Get as many hours as you can per thermal cycle. A few long trips are much easier on your engine than a lot of short hops. Long-range tanks are terrific if they let you cut down on fuel stops. Training flights are the worst—train in someone else's airplane if you can.

  5. Warm up and cool down gradually.

    • Don't be in a hurry to take off. Allow plenty of warm-up time between engine start and departure. The colder the OAT, the more important this is.

    • Throttle-up very slowly at takeoff. Each takeoff involves going from idle to max power. Do this as gradually as conditions permit. One excellent technique: (1) taxi into position and hold; (2) throttle-up slowly to 50% power with brakes locked; (3) check all engine instruments; (4) release the brakes; (5) throttle-up smoothly from 50% to 100% power while on-the-roll, taking at least 10 seconds to reach full power.

    • Practice programmed cool-down procedures on every descent. A good rule is to figure out how many inches of MP you need to lose to transition from cruise to approach or pattern speed, then use your DME, LORAN, or GPS time-to-station readout to begin a programmed cool-down that many minutes out. Reduce power no faster than 2" MP every 2 minutes. Use a stopwatch, don't guess.

  6. Use conservative power settings.

    • If you operate your engine at the high end of the envelope, you are trading performance for longevity. Your engine will last longer if you use more conservative power settings. This is especially true when it comes to turbocharged engines.

    • Cruising at 65% power is an excellent tradeoff. In exchange for the few knots you give up, you gain significant fuel economy, cooler engine temperatures, longer engine life, and a quieter cabin.

  7. Operate oversquare!

    • The old saw about never allowing MP to exceed RPM/100 is bunk! Continental authorizes cruise operation at 1 to 3 inches "oversquare" for most normally-aspirated engines, and allows 9 to 12 inches "oversquare" for most turbocharged engines. Check the cruise charts in your POH or obtain the Continental operator's manual for your engine. Operating at minimum RPM and maximum MP (within the allowable envelope) actually helps your engine last longer.

    • Cruise at the lowest RPM and highest MP that the book allows for the percentage of power that you desire. You usually have several possible RPM/MP combinations to choose from at lower altitudes in a normally-aspirated airplane, and at virtually all altitudes in a turbocharged airplane.

    • Low RPM operation provides numerous benefits: better cylinder compression, lower frictional losses, improved propeller efficiency, cooler-running valves, lower EGTs and TITs, and a quieter cabin.

  8. Maintain optimal CHTs (350 -425 F).

    • High CHTs are bad for your engine. The aluminum alloy used in your cylinder heads begins to lose its strength as the CHT rises above about 400 F. Excessive CHTs over a long period of time can result in head cracks or even catastrophic head-to-barrel separations. Even though your CHT redline is 460 F, you should try to keep your CHTs at or below 400 F for normally-aspirated engines or 425 F for turbocharged engines. Do this by opening cowl flaps, increasing airspeed, reducing power, and/or enrichening (listed in descending order of desirability).

    • Low CHTs aren't great, either. Cooler-than-optimum CHTs (say, in the low 300's F) can result in increased deposits on spark plugs and exhaust valve stems. The latter will ultimately result in accelerated exhaust valve guide wear and a premature top overhaul. Try to keep your CHTs at 350 F or more.

  9. Keep baffle seals in tip-top shape.

    • Flexible baffle seals are crucial to proper engine cooling. If any air is able to leak past the baffle seals (between the rigid baffles and the cowling), the cylinders can develop serious hot spots. Inspect the baffle seals at every preflight, and immediately replace any seals that have deteriorated.

    • Baffle seals must always fold up/forward, never down/backward! Engine cooling requires that there be a high pressure area above the cylinders and a low pressure are below them. The baffle seals must be oriented so that this pressure differential presses them tightly against the cowling. Any seals that fold downward or backward will allow air to bypass the cylinders.

    • Black rubber baffle seal material is trash. It typically loses its sealing ability in just a few hundred hours. Always use silicone baffle seal material available from RAM (red) or Victor (blue). It will last to TBO or beyond.

  10. Fix exhaust leaks immediately.

    • Exhaust gas is incredibly corrosive. Small exhaust leaks turn into big ones amazingly fast. Exhaust leaks often occur at the cylinder exhaust ports where the exhaust riser flanges attach. Leaking exhaust quickly erodes the soft aluminum at the exhaust port, necessitating costly cylinder removal and reconditioning.

    • Exhaust leaks are easy to spot. They leave telltale red, orange, or yellow stains. Inspect for them every time you preflight. If you spot a leak (even a tiny one), get it fixed right away.

  11. Lean aggressively (but prudently).

    • Most pilots operate their engine much too rich. The result is usually trouble: fouled sparkplugs, accelerated exhaust valve guide wear, and stuck exhaust valves.

    • Lean as aggressively as the book allows. For Continental engines, lean right to peak EGT at cruise power settings of 65% or below. At 75% cruise, lean to 50 F rich of peak. For cruise climb, lean to 125 F rich of peak for best power and extra cooling. Above 75%, operate full-rich—this is normally confined to takeoff or go-around.

    • For turbocharged engines, limit TIT to 1600 F (50 below redline). Do this by reducing RPM, reducing power, and/or enrichening (listed in descending order of desirability).

    • Lean during all ground operations except for engine start. It is particularly important to lean for taxi and runup. Since EGT is usually low-offscale at idle power, the best method is to lean for peak RPM at idle. You should see about a 50 RPM rise as you lean slowly. If you don't, your idle mixture is adjusted too lean—tell your A&P.