You may be prepared for winter, but is your light aircraft also ready? Chances are that when temperatures plummet and the snow moves in you’re not going to be flying in a hurry. The aircraft at greatest risk are those that are parked outside, and those along the coast or close to lakes and rivers where corrosion damage is a major risk. Those facing minimal risk are the ones that are in the few dry parts of the country where industrial pollutants are not an issue.
While the best solution is to store aircraft indoors, in a hangar, this isn’t always possible. But whether it is or not, there are steps that owners can take, including removing engines from the body of the aircraft for the winter months.
Small Aircraft Engine Care
US engine manufacturer, Lycoming warns that active corrosion can be found on the cylinder walls of new engines that haven’t been operated for even short, two-day periods of time. On the other hand, those that have been used for at least 50 hours acquire a kind of “varnish” that protects them from corrosion, and they can be left inactive for weeks without any danger of corrosive damage.
Engines that are not going to be used for flight need to 
be stored or preserved in some way to minimize any possibility of corrosion. Acceptable methods are aimed at preventing moisture and other agents that might cause corrosion from affecting the metal surfaces in the engine.
Lycoming also warns that engines should not be pulled through by hand to minimize corrosion and rust because the rings have the effect of wiping oil from the walls of cylinders and reducing the lubrication needed for other parts of the engine including the cam and cylinders. The company notes that pulling the prop before starting the engine is a different issue because it does lubricate the parts. It also has the effect of checking valve condition.
Preservation of Engines That Will Not be Active for a Month or More
It is essential to “preserve” engines that will not be active for more than a month, particularly when the aircraft is located in a humid environment or somewhere close to salt water.
Of course the process that should be followed will depend on the engine make and design, and the manufacturer’s instructions should always be followed. These will normally include a basic procedure including:
- Draining lubricating oil from the sump and replacing it with a preservative oil
- Operating the engine to “normal” temperatures before shutting down
- Removing spark plugs, spraying the holes with a preservative oil mixture, and then replacing the spark plugs
- Installing dehydrating agents (desiccants) and moisture-impervious material to protect intake and exhaust passages
- Tagging the propeller so that anyone with access to the aircraft knows that the engine is “preserved” and that they must not turn the propeller
While corrosion-preventive compounds do effectively work as insulators from moisture over fairly long periods of time, they can dry out when solvents evaporate. For this reason, if engines have been removed from aircraft, they should be stored in containers that are airtight, and the containers should be packed with dehydrating agents and sealed. Adding cobalt chloride to silica gel (which is the most common desiccant) can be very effective because the bright blue color from the cobalt chloride will show low moisture levels. If the blue gets lighter (changing from lavender to pink and even white), this indicates higher humidity levels. The ideal is that when the color remains blue the conditions for storage are safe and dry.
Other Safeguards for Your Aircraft
If you are planning to store your aircraft engine, it really should be coated with a compound that will prevent it from corrosion. Close or plug holes and treat propeller shafts or wrap them with a suitable barrier paper. Purge fuel systems.
This said, there are different recommendations for different aircraft, and it is essential that you familiarize yourself with specifics. For example if your plane has rubber-type flexible fuel bladders, it is best to keep the tanks full to ensure that the membrane doesn’t crack.
Returning Aircraft to Service
Once winter is over, all seals, tape and desiccant bags must be removed and any residue from tape must be cleaned. Any dehydrator or spark plugs that have been used should be removed. Preflight checks are also critically important for safety reasons.
Long-term engine preservation can result in large quantities of oil being trapped in the cylinders. The oil should be drained before the engine is rotated otherwise you risk piston, crankshaft or other damage.
If you are in any doubt, contact the manufacturer of the aircraft and/or the engine.
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