From time to time, and for a number of reasons, airplane owners will find they need to stop flying for an extended period of time. It's not on any pilot's wish list, but it happens. And if it happens to you—as it has to me—actions need to be taken to preserve your engine during a period of inactivity.
What's "normal" engine activity?
The Lycoming Service Letter quote at the beginning of this article was included only to get your attention. The next statement in the same letter says that engines that have been flown for 50 hours over a relatively short period will have some protection against corrosion due to a buildup of varnish. Once the varnish layer is there, and in favorable (i.e., average) atmospheric conditions, an engine may remain inactive for several weeks without evidence of damage by corrosion.
The bulletin goes on to state that the desired flight time for air-cooled engines is at least one continuous hour with oil temperatures from 165 degrees to 200 degrees F at intervals not to exceed 30 days.
Service Information Letter SIL99-1 from Continental Motors, Inc. also addresses engine preservation. It weighs in on the issue of corrosion by stating "the best method of reducing the likelihood of corrosive attack is to fly the aircraft at least once a week for a minimum of one hour."
Lycoming says that flying once a month for an hour is adequate, while Continental says that once a week is adequate to keep rust at bay. What's the right answer?
The right answer for your airplane depends on the environment. SIL99-1 states that corrosion is "influenced by geographical location, season and usage," while L180B states that "if the airplane is operated close to lakes, oceans, rivers and in humid regions there's a greater need for engine preservation than those operated in arid regions."
Clean oil reduces potential for corrosion
Flying often and changing the oil and filter (or cleaning the screen) every four months or at the engine manufacturer's recommended interval (25 hours for engines with pressure screen; 50 hours for engines with an oil filter) are commonly recognized practices for keeping engine corrosion at bay. But since filters can't remove acids or water from oil, these practices alone won't fully protect an engine against corrosion.
The package of additives in today's ashless dispersant oils do a pretty good job of both preventing the formation of excessive carbon deposits and "grabbing" acids so they can be drained at each oil change. (Acids are formed when partially-burned fuel combines with water produced during the normal combustion process.)
However, tests reveal that the dispersant packages folded into these oils slowly lose effectiveness after 25 to 30 hours of use, especially in infrequently-flown or tired engines. Based on this, the engine of the average GA airplane will be better protected against rust when the owner shortens the "hours flown" interval for changing the oil and the filter.
Always change oil at each four-month calendar time interval—no matter how many hours on the oil. Keep the 25-hour limit if the engine has an oil screen; shorten the change interval to 30 or 35 hours if you have a filter.
If you can't fly for a period of more than 30 days, both Lycoming and Continental Motors (CMI) recommend putting the engine into storage. Lycoming and CMI divide these storage periods into two categories: temporary and indefinite.
Temporary storage (30 to 90 days)
Continental Service Information Letter SIL99-1, "Engine Preservation for Active and Stored Aircraft" defines temporary storage as an engine that will not be operated for 30 to 90 days.
The preservation process consists of these steps:
1) Drain engine oil before filling sump with oil conforming to MIL-C-6529 Type II. Run the engine for one hour at normal operating temperature.
2) Remove the top spark plugs. Using a common garden sprayer or equivalent, spray atomized preservative oil conforming to MIL-P-46002, Grade 1 at room temperature through the upper spark plug hole. Rotate engine as necessary to provide a complete coating of all cylinder walls.
3) Reinstall top spark plugs.
4) Seal all engine openings (breather tube, carburetor or fuel injection air inlet, exhaust pipes, etc.) and attach a "Remove Before Flight" streamer at each location.
5) Attach a "Do Not Turn Propeller–Engine Preserved–Preservation Date _____" flag to the propeller.
Indefinite storage (More than 90 days)
CMI's procedure for indefinite storage includes the steps above, with a few changes:
• Instead of reinstalling the spark plugs, install dehydrator spark plugs (MS27215-1 or -2; or AN4062-1) in the upper spark plug holes.
• Seal the openings listed in Step 4 with a bag filled with silica gel desiccant beads.
In order to maintain the indefinite preservation, the desiccant must be inspected every 15 days. If the beads change from bright cobalt blue to a pinkish color, the desiccant must be dried prior to further use. Desiccant beads are dried by heating in an oven at 200 to 220 degrees F until the blue color returns.
CMI says that indefinite storage is maintained when all cylinder bores are re-sprayed with the corrosion-preventive mixture every 90 days.
The MIL-C-6529 Type II oil listed by both Lycoming and Continental for preservation consists of three parts aircraft mineral engine oil and one part MIL-L-6529 Type I preservative (such as AeroShell Fluid 2XN).
But there's no need to mix this yourself—both Phillips Aviation Anti-Rust 20W-50 and AeroShell Fluid 2F comply with the MIL-L-6529 Type II specification in the bulletins and are readily available in aviation supply houses.
While Continental recommends in its Service Letter (SILs aren't mandatory) that the engine oil sump be drained of preservative oil prior to returning the engine to service, AeroShell Fluid 2F and Phillips Aviation Anti-Rust 20W-50 oils may be used temporarily. They do not, however, contain the anti-wear/anti-corrosion additive package in ashless dispersant oils—and use should not exceed 50 hours over the life of the engine TBO period. Both are termed "flyaway" oils.
Using these oils vastly simplifies the transition between storage and returning an engine to service since there's no need to drain and refill the oil sump with new oil prior to the first flight. Remove the bottom spark plugs or desiccant plugs, install the spark plugs and unseal all the openings, give the engine a thorough preflight inspection and go flying.
After a flight or two, drain the preservative oil while the oil is hot and go back to using the ashless dispersant oil of your choice.
Upper cylinder rust inhibitors
Two products that conform to the MIL-P-46002 specification are listed in SIL99-2C, titled "Sealants, Lubricants and Adhesives Authorized by CMI." They are MotorStor Oil Preservative marketed by Graham Aircraft Engines and NoxRust VCI-105 by Daubert Chemical.
According to data sheets at the Daubert Chemical website, the NoxRust product is a combination of preservative oils and vapor corrosion inhibitors (VCI).
The engine builders at Graham Aircraft Engines—a large and reputable piston engine overhaul facility in Newnan, Ga.—told me that they spray MotorStor into their rebuilt and overhauled engines prior to shipping. Graham sells MotorStor by the case or individually in aerosol spray cans.
Tanis Aircraft makes it easy
Tanis Aircraft of Blaine, Minn. is the pioneer in engine-mounted preheating systems, and the company also sells engine preservation kits. Buying one of the Tanis kits can greatly simplify engine preservation chores.
Tanis' TU20000-4 and TU20000-6 kits contain everything needed to comply with the Lycoming and CMI Indefinite Storage guidelines; all that's needed is the additional purchase of a sufficient quantity of mineral oil to mix with the MIL-L-6529 Type I preservative oil in the kit to complete the preservation.
There are also some field-developed methods—that differ greatly from the Lycoming and CMI methods—of keeping rust out of an engine. AvBlend is one additive which many owners use; CamGuard is another.
CamGuard is an FAA-accepted engine oil additive formulated to provide rust and corrosion control. In normal use, it's added to every fresh oil change at a ratio of five parts to 100 (5 percent, or 1.6 fluid ounces per quart). The product was developed by Ed Kollin, a research chemist who has worked with Exxon Research and Engineering.
In November 2014, CMI agreed to test CamGuard for an 18-month period. According to Kollin, as quoted from a CMI press release, "Aviation oils lack the latest available lubrication technology because they are essentially blended to Navy piston engine requirements from the middle of the last century."
Kollin developed the CamGuard additive package while at Exxon, but according to Kollin, Exxon decided not to use it. After he left Exxon, Kollin spent a year developing today's CamGuard additive. The product addresses the corrosion, deposit and wear control shortcomings in aviation oils, according to Kollin.
I called Kollin to find out more about CamGuard. He told me that Alaskan flyers have said they have had good luck keeping corrosion at bay by adding CamGuard in a 1:10 ratio to engine oil. They then run the engine to coat the interior and seal the openings to keep out moisture.
Pickling an engine
The steps listed in both the Lycoming and CMI bulletins are referred to as "pickling" an engine. There are also other methods, some home-grown, some logical—and a few that can only be used in certain locales. The following are a few of these.
Drown it in oil
One method of engine preservation consists of removing the engine accessories, sealing the accessory mounting pads with "blank off" plates and filling the engine with inexpensive automotive engine oil.
It works well—but is rarely used when the engine is mounted on the airframe. It's also very time-consuming to remove all the residual oil prior to returning the engine to service.
Heat it up
Another approach consists of keeping the engine warm enough that moisture can't condense on surfaces inside the engine. If the air temperature inside the engine never cools enough to allow condensation to form in the engine, corrosion won't take place.
One experienced mechanic I spoke to told me about a low-cost method that involves building a tent that surrounds the engine (or installing a purpose-built engine cover) and positioning a small 110 VAC electric heater to direct warm air into the tent (or cover). Of course, a heated hangar is the best environment to do this.
There's only one caveat when using the heat-it-up method: increases in air temperature can result in rapid increases in corrosion formation. That's why the ramp at Miami is called "Corrosion Corner."
Dry it out
Another method relies on preventing moisture-laden air from entering the engine. CFA supporter Tempest Plus sells AA1000 Engine Preservation System for that purpose.
The system is powered by 110 VAC, is self-contained and operates as an open-loop system that draws ambient air through a bag of desiccant beads in a lidded box. This dries the air prior to pumping it into the engine through fittings via the oil filler tube. The dried air circulates through the engine then exits through the crankcase breather tube.
Similar products include Smart Engine Saver and Black Max Ultimate Engine Saver by ACI Products of Florida.
Note: both the heat-it-up and the dry-it-out methods require continuous use of 110 VAC power.
Lycoming's new preservation scheme
Lycoming Service Letter L180B also provides details about a second preservative scheme that differs considerably from traditional five- or six-step pickling schemes.
Lycoming's traditional scheme which uses preservative-type oils of the type mentioned earlier is in essence identical to the Continental procedure, but Lycoming's newer scheme is much easier. It consists of adding Cortec VpCI-326 preservative concentrate to clean ashless dispersant-type engine oil at a ratio of one part VpCI-326 to 10 parts oil.
The engine is then operated until normal operating temperatures are obtained. After shutdown, the top spark plugs are removed and two fluid ounces of the preservative mixture is sprayed in each cylinder. This procedure is printed on each quart bottle of VpCI-326.
According to Andrew Wroblewski, technical sales manager at Cortec Corp., VpCI-326 is a very strong vapor phase corrosion inhibitor. Wroblewski said the product can also be used by fogging it with a spray applicator into an engine.
The belt-and-suspenders way
Since I knew I wouldn't be flying for as long as a year, I called Kollin for advice about how to pickle my airplane's engine.
First, he told me that he would make sure the engine was filled with clean oil. I asked about using Phillips 20W-50 Anti-Rust oil—I had already bought it—and Kollin said to go ahead. He recommended that I add enough CamGuard to make up the 10 percent ratio.
Then, according to Kollin, I needed to run the engine until the oil temperature warmed up to 110 to 125 degrees. I did a high-speed taxi that resulted in 180-degree oil.
Kollin advised that after returning to the hangar and while the engine was still hot, I should add VpCI-326 to make a 10 percent ratio to the oil/CamGuard. He said all I would need to do to "activate" the vapor phase of this lubricant cocktail was remove the top spark plugs and spin the engine for 15 to 20 seconds with the starter.
The preservative oil combined with the vapor phase corrosion inhibitor provides complete engine protection—and I consider it a belt-and-suspenders method. When I'm ready to fly again, I'll make a short flight to warm up my oil preservation cocktail, then drain the oil and fill my engine with ashless dispersant oil. I may have overdone it, but I'm taking no chances when it comes to preserving my low-time engine.
Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He's a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to .
Lycoming Service Letter L180B, "Engine Preservation for Active
and Stored Aircraft"
Continental Motors Inc. Service Information Letter SIL99-1,
"Engine Preservation for Active
and Stored Aircraft"
SIL 99-2C, "Sealants, Lubricants
and Adhesives Authorized by CMI"
MotorStor oil preservative
Graham Aircraft Engines
TU20000-4 and TU20000-6 engine preservation kits
CamGuard engine oil additive
AA1000 engine preservation system
Smart Engine Saver; Black Max Ultimate Engine Saver
Aircraft Components Inc. (ACI)
Cortec VpCI-326 preservative